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IIII._II11_ I! 11‘ l.- HI .3; -; '; : fl . 2mg University This is to certify that the thesis entitled ROTATIONAL TRACTION AT THE AMERICAN FOOTBALL SHOE- SURFACE INTERFACE AND ITS APPLICATION TO ANKLE ._ INJURY presented by MARK R. VILLWOCK has been accepted towards fulfillment of the requirements for the MS. degree in Engineering Mechanics Major Pro essor’s Signature 03:135/09 Date MSU is an Affirmative Action/Equal Opportunity Employer _.—.---.-.u—c_.-n—o-l-l-I-l--u-o-l-I-I- _. _._.-A.—-.—.-a-.---.-n-a-o-o-o-o'.o--.A--;-I-J-o-¢—~—~—--—~. - PLACE IN RETURN BOX to remove this checkout from your record. To AVOID FINES return on or before date due. MAY BE RECALLED with earlier due date if requested. DATE DUE DATE DUE DATE DUE 45% WW 5108 K:IProj/Aoc&Pres/ClRC/DateDue.indd ROTATIONAL TRACTION AT THE AMERICAN FOOTBALL SHOE-SURFACE INTERFACE AND ITS APPLICATION TO ANKLE INJURY By Mark R. Villwock A THESIS Submitted to Michigan State University in partial fi11fi11ment Of the requirements for the degree of MASTER OF SCIENCE Engineering Mechanics 2009 ABSTRACT ROTATIONAL TRACTION AT THE AMERICAN FOOTBALL SHOE-SURFACE INTERFACE AND ITS APPLICATION TO ANKLE INJURY By Mark R. Villwock While linear traction is necessary during an athletic contest, it is generally accepted that excessive rotational traction results in high forces being transmitted to vulnerable anatomic structures which may then precipitate ankle and knee injuries. Our laboratory has combined mechanical testing of the football shoe-surface interface with human cadaver experiments to investigate rotational traction and its application to ankle injury. Chapter 1 provides an overview of artificial surfaces and documents injuries that may be related to the shoe-surface interface. In Chapter 2, rotational traction measurements are documented for ten football shoes across four surfaces. The artificial surfaces were found to exhibit higher peak torque and rotational stiffness in comparison to natural grass. Chapter 3 further investigates rotational traction on third-generation, artificial surfaces. Infill material and fiber type were found to significantly affect peak torque. Chapter 4 presents the results Of a cadaver study on ankle injuries generated by excessive external rotation of the foot/ankle complex. The method Of foot constraint affected the mode Of failure and the amount of foot rotation at failure. Chapter 5 documents the development Of a biofidelic ankle that may be used to assess the risk of ankle injury for various shoe-surface interfaces. Finally, Chapter 6 provides a synopsis of this thesis and Offers recommendations for future areas of research. The data presented in this thesis may be applicable to injury prediction and be helpful in the development of future strategies for injury prevention. ACKNOWLEDGMENTS I would like to thank my advisor, Dr. Roger Haut, for his guidance, expertise and support during my research at the Orthopaedic Biomechanics Laboratories. I would also like to thank Dr. John Powell and Dr. Neil Wright for their insight and for serving on my committee. I acknowledge Eric Meyer whose suggestions and assistance was Of profound support during both the testing period of my research as well as analysis. I would like to thank Clifford Beckett for his knowledge and technical support. I would also like to thank and acknowledge all of my colleagues at the Orthopaedic Biomechanics Laboratories; Tim Baumer, Jerrod Braman, Dan Isaac, Nurit Golenberg, Brian Powell, and Feng Wei. iii TABLE OF CONTENTS LIST OF TABLES ..................................................................................................... vi LIST OF FIGURES ................................................................................................... ix LIST OF PUBLICATIONS ....................................................................................... xii CHAPTER 1 INTRODUCTION ..................................................................................................... 1 CHAPTER 2 FOOTBALL PLAYING SURFACE AND SHOE DESIGN AFFECT ROTATIONAL TRACTION .................................................................................... 10 Abstract .......................................................................................................... 10 Introduction ................................................................................................... 1 1 Materials and Methods .................................................................................. 13 Results ........................................................................................................... 19 Discussion ...................................................................................................... 26 References ..................................................................................................... 3 1 CHAPTER 3 THE EFFECTS OF VARIOUS INFILLS AND FIBER STRUCTURES ON GENERATING ROTATIONAL TRACTION ON AN ARTIFICIAL SURFACE ................................................................................................................. 34 Abstract......................._ ................................................................................... 34 Introduction ................................................................................................... 35 Materials and Methods .................................................................................. 37 Results ........................................................................................................... 44 Discussion ...................................................................................................... 49 References ..................................................................................................... 53 CHAPTER 4 EXTERNAL ROTATION ANKLE INJURIES - INVESTIGATING LIGAMENTOUS RUPTURE ................................................................................... 56 Abstract .......................................................................................................... 56 Introduction ................................................................................................... 57 Materials and Methods .................................................................................. 60 Results ........................................................................................................... 65 Discussion ...................................................................................................... 72 References ........................................................................................... . .......... 77 iv CHAPTER 5 DEVELOPMENT AND EVALUATION OF A SURROGATE ANKLE FOR USE WITH A ROTATIONAL TRACTION APPARATUS ........................... 80 Abstract .......................................................................................................... 80 Introduction ................................................................................................... 81 Materials and Methods .................................................................................. 82 Results ........................................................................................................... 87 Discussion ...................................................................................................... 94 References ..................................................................................................... 98 CHAPTER 6 CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE RESEARCH .............................................................................................................. 100 APPENDICES ........................................................................................................... 105 Appendix A: Peak torque, rotational stiffness and temperature data from Chapters 2 and 3 .............................................................. 105 Appendix B: Standard Operating procedure for measurement of rotational traction on the football shoe-surface interface .................................................................................... 121 Appendix C: Standard operating procedure for analysis of rotational traction data .............................................................................. 127 Appendix D: Standard operating procedure for torsional experiments of the cadaver ankle ............................................. 134 Appendix E: Standard Operating procedure for ankle motion analysis ..................................................................................... 152 LIST OF TABLES Table 2.1: Description Of tested football shoes ......................................................... 15 Table 2.2: Rotational stiffness -Nm/deg; mean Of five trials (SD). # indicates significant difference from natural grass surfaces (p < 0.001) .............................................................................................. 22 Table 2.3: Peak torque — Nm; mean of five trials (SD). * indicates significant difference from all other surfaces (p = 0.008). # indicates significant difference from natural grass surfaces (p < 0.001). + indicates significant difference from all other shoe models (p < 0.001) ................................................................................. 23 Table 2.4: Rotational stiffness post-hoe comparison between shoe models ............. 25 Table 3.1: Description of tested football shoes ......................................................... 40 Table 3.2: Peak torque — Nm; mean of five trials (SD) ............................................. 45 Table 3.3: Infill size as measured using particles in a 50 cc container ...................... 48 Table 3.4: Air temperature during rotational traction testing - degrees C; mean temperature (SD) ............................................................................ 48 Table 4.1: Torque and angle of foot/ankle complex rotation at failure (foot constrained in potting material). * indicates torque and angle information lost due to data acquisition program malfunction ............... 66 Table 4.2: Torque and angle of foot/ankle complex rotation at failure (foot constrained with athletic tape) ................................................................. 69 Table 4.3: Motion analysis results from trial immediately preceding failure (potted foot group). Positive translation is in the medial and posterior direction. Positive flexion is plantarflexion ............................ 71 Table 4.4: Motion analysis results from trial immediately preceding failure (taped foot group). Positive translation is in the medial and posterior direction. Positive flexion is plantarflexion ............................ 71 vi Table 5.1: Torsional stiffness values (Nm/deg). The primary stiffness was determined in a linear regression through all data points up to 20 degrees of foot/ankle complex rotation. The secondary stiffness was then determined in a linear regression through all data points above 35 degrees of foot/ankle complex rotation. The overall stiffness was based on a linear regression through the entire data set ........................................................................................... 89 Table A1: Peak torque Of Gameday Grass surfaces with cryogenic infill (Nm) ......................................................................................................... 105 Table A2: Peak torque Of Gameday Grass surfaces with cryogenic infill continued (Nm) ........................................................................................ 106 Table A3: Peak torque of Gameday Grass surfaces with extruded infill (Nm) ....................................................................................................... 107 Table A4: Peak torque of Gameday Grass surfaces with extruded infill continued (Nm) ...................................................................................... 108 Table A5: Peak torque of Gameday Grass surfaces with ambient infill (Nm) .......... 109 Table A6: Peak torque Of Gameday Grass surfaces with ambient infill continued (Nm) ...................................................................................... 110 Table A7: Peak torque Of F ieldTurf, AstroPlay, and natural grass surfaces (Nm) ......................................................................................................... 111 Table A8: Peak torque Of FieldTurf, AstroPlay, and natural grass surfaces continued (Nm) ........................................................................................ 112 Table A9: Rotational stiffness of Gameday Grass surfaces with cryogenic infill (Nm/degree) .................................................................................... l 13 Table A10: Rotational stiffness of Gameday Grass surfaces with cryogenic infill continued (Nm/degree) .................................................................. 114 Table A11: Rotational stiffness of Gameday Grass surfaces with extruded infill (Nm/degree) .................................................................................. 1 15 Table A12: Rotational stiffness Of Gameday Grass surfaces with extruded infill continued (Nth/degree) .................................................................. 116 Table A13: Rotational stiffness of Gameday Grass surfaces with ambient infill (Nm/degree) ................................................................................. 1 17 vii Table A14: Rotational stiffness of Gameday Grass surfaces with ambient infill continued (Nm/degree) ................................................................ 118 Table A15: Rotational stiffness of AstroPlay, FieldTurf, and natural grass surfaces (Nm/degree) ............................................................................. 119 Table A16: Rotational stiffness Of AstroPlay, FieldTurf, and natural grass surfaces continued (Nth/degree) ............................................................ 120 Table E1: Segment order and marker labels for a test subject in Vicon ................... 152 viii LIST OF FIGURES Figure 2.1: Description of rotational traction testing apparatus ................................ 17 Figure 2.2A: The representative shape of the torque vs. shoe rotation plot that consisted Of four regions (initial breakaway, build-up, slippage, unloading). The percent of rotation that occurred in each region was dependent on the shoe-surface combination and varied between shoes and surfaces ............................................... 20 Figure 2.23: The representative shape of the torque vs. shoe rotation plot that consisted of three regions (omission of slippage) ........................ 20 Figure 3.1: Infills (upper left to right) — A (cryogenic SBR), B (ambient SBR), C (extruded TPE); Fibers (lower left to right) — I (monofilament), 11 (parallel slit), III (monofilament with nylon root zone) ............................................................................................... 38 Figure 3.2: Description Of rotational traction testing apparatus ................................ 42 Figure 3.3: Box plot of peak torque across shoes for each infill. The line near the center Of the box represents the median value, the box represents the inter-quartile range and the whiskers represent the range. * indicates significant difference compared to other infills ..................................................................................................... 46 Figure 3.4: Box plot Of peak torque across shoes for each fiber. The line near the center of the box represents the median value, the box represents the inter-quartile range and the whiskers represent the range. * indicates significant difference compared to other fibers ..................................................................................................... 46 Figure 3.5: Box plot Of peak torque across surfaces for each shoe type. The line near the center Of the box represents the median value, the box represents the inter-quartile range and the whiskers represent the range. ~ indicates significant difference with respect to Hybrid, 7 Studded, and Turf designs. (2 indicates significant difference with respect to 12 Studded, Edge and Turf designs. A indicates significant difference with respect to all other cleat designs ........................................................... 47 ix Figure 4.1: Close-up Of cadaveric lower extremity mounted in testing device with foot constrained in potting material. Reflective marker arrays were used to conduct motion analysis using a Vicon system ........................................................................................ 61 Figure 4.2: Cadaveric lower extremity with foot constrained to polycarbonate plate with athletic tape. The polycarbonate plate is inserted into a rigid fixture for testing. Reflective marker arrays were used to conduct motion analysis using a Vicon system ..................................................................................... 62 Figure 4.3: Experimental setup performed on biaxial materials testing machine ................................................................................................. 62 Figure 4.4: F ibular avulsion Of the posterior talofibular ligament ............................ 67 Figure 4.5: Fibular fracture through the anterior tibiofibular ligament........ ............. 67 Figure 4.6: Anterior deltoid rupture .......................................................................... 70 Figure 4.7: Rotation dependent injury mechanism may involve the player lying prone as another player lands on his ankle, forcing the foot to externally rotate ......................................................................... 74 Figure 5.1: Rotational traction testing apparatus (V illwock et al., 2009a; 2009b) .................................................................................................... 84 Figure 5.2: Posterior view of the surrogate lower extremity. An angular displacement transducer inside of the tibia shaft recorded foot/ankle complex rotation. The channel was filled with neoprene rubber to simulate the torsional stiffness Of the ankle ............ 84 Figure 5.3: Surrogate lower extremity mounted on materials testing machine ................................................................................................. 86 Figure 5.4: Torque versus foot/ankle complex rotation from a cadaver study by Villwock et al. (20090). This graph depicts the average results, with standard deviations, calculated from ten cadaver lower extremities in five degree incremental trials. Trendlines are included for the primary and secondary torsional stiffnesses. The data used to construct this graph does not include the failure-level experiments ..................................................... 88 Figure 5.5: Torque versus foot/ankle complex rotation data from the surrogate tests. The results are fiom neoprene rubber bumpers Of varying hardness, as measured on the durometer Shore A hardness scale. Trendlines are included for the primary and secondary torsional stiffness ................................................................. 90 Figure 5.6: Box plot of peak torque (Nm) for each shoe. The line near the center of the box represents the median value, the box represents the inter-quartile range and the whiskers represent the range. Arrows represent significant differences (p <0.05). ............. 91 Figure 5.7: Box plot of rotational stiffness (Nm/deg) for each shoe. The line near the center of the box represents the median value, the box represents the inter-quartile range and the whiskers represent the range. Arrows represent significant differences (p <0.05). ................................................................................................ 92 Figure 5.8: Box plot of peak rotation of the ankle (degrees) for each shoe. The line near the center Of the box represents the median value, the box represents the inter-quartile range and the whiskers represent the range. Arrows represent significant differences (p <0.05). ................................................................................................ 93 Figure B1: Live readout of the labview program during a rotational traction test ............................................................................................................ 125 Figure B2: Key components Of the rotational traction apparatus .............................. 126 Figure C1: Procedure for potting the proximal end Of the cadaver lower extremity ................................................................................................ 137 Figure C2: Potted foot constraint with fixation screws into the calcaneous ............. 138 Figure C3: Specimen prepared for testing with taped foot constraint ....................... 139 Figure C4: Computated tomography procedure for ankle specimen ......................... 141 xi LIST OF PUBLICATIONS Peer-Reviewed Manuscripts Villwock MR, Meyer EG, Powell JP, Fouty AJ, Haut RC. (2009) Football playing surface and shoe design affect rotational traction. Am J Sports Med. 37 (3):5 1 8-525. Villwock MR, Meyer EG, Powell JP, Fouty AJ, Haut RC. (2009) The effects Of various infills, fiber structures, and shoe designs on generating rotational traction on an artificial surface. J Sports Eng Tech. 223(1):1 1-19. Villwock MR, Meyer EG, Powell JP, Haut RC. A biomechanical investigation of ankle injury under external foot/ankle complex rotation using the human cadaver model. J Appl Biomech. In Review. Villwock MR, Meyer EG, Powell JP, Haut RC. Development and evaluation of a surrogate ankle for use with a rotational traction apparatus. J Sports Eng Tech. In Review. Meyer EG, Villwock MR, Haut RC. Osteochondral microdamage from valgus bending of the knee. Clin Biomech. In Review. Déjardin LM, Cabassu JB, Villwock MR, Malinowski R, Haut RC. In vivo evaluation Of a novel angle stable interlocking nail for the stabilization Of tibial fiactures in dogs. In Preparation. Peer-Reviewed Abstracts Villwock MR, Meyer EG, Powell JP, Fouty AJ, Haut RC. (2008) Football playing surface components may affect lower extremity injury risk. North American Congress on Biomechanics; Ann Arbor, MI: American and Canadian Society of Biomechanics. Villwock MR, Meyer EG, Powell JP, Fouty AJ, Haut RC. (2008) Football shoe designs may affect lower extremity injury risk. North American Congress on Biomechanics; Ann Arbor, MI: American and Canadian Society Of Biomechanics. Villwock MR, Meyer EG, Powell JP, Haut RC. (2009) External rotation ankle injuries: Investigating ligarnentous rupture. Summer Bioengineering Conference; lake Tahoe, CA: American Society of Mechanical Engineering. Cabassu JB, Villwock MR, Malinowski R, Haut RC, Déjardin LM. (2009). In vivo biomechanical evaluation Of a novel angle-stable interlocking nail for diaphyseal fracture stabilization in dogs. ACVS Symposium; Washington, DC: American College of Veterinary Surgeons. xii Powell JP, Villwock MR, Fouty AJ, Haut RC. Impact accelerations on different types of football playing surfaces. 2009 National Athletic Trainers’ Association Annual Meeting and Clinical Syrnposia. San Antonio, TX: National Athletic Trainers’ Association. xiii Chapter 1: Artificial Surfaces and Injury Risk A study of high school football in Pennsylvania noted that 21% of the reported injuries were classified as either definitely or possibly field related (Harper et al., 1984). Two important interactions between the player and the surface are: the amount Of energy absorbed by the surface during an impact (hardness), and the type Of footing a surface provides (traction) (Rogers and Waddington, 1992). If the surface is excessively hard, high impact forces may result in compression fractures and the increased risk of injury during a fall (Adrian and Xu, 1990; Henderson et al., 1990). If the surface is too soft, player fatigue and performance may be affected (Henderson et al., 1990). The extremes of traction also pose similar tradeoffs between player performance and player safety. A certain level of traction is necessary for speed and agility, but too much traction can excessively stress joints and lead to lower extremity injury (McNitt et al., 1996). Lower extremity injuries represent over half of the time loss injuries in football (Fernandez et al., 2007). Among the many factors that are associated with these injuries are the fractional characteristics of the shoe—surface interface. Frequently, the mechanism of injury involves a foot planted, or “fixated”, on the ground while the upper body is excessively rotated. This can occur in noncontact situations, for example, when a player twists after a jump landing, and as a result Of contact with another player. The resulting injuries range from mild lateral ankle sprains to ACL rupture (Boytim et al., 1991; Guise et al., 1976). Historically, sporting events such as American football have occurred on natural grass fields. A natural grass field in a stadium may withstand 50 to 100 hours per year Of hard usage and, even then, requires constant maintenance to retain its quality (Gorharn and Orofino, 1996). With the growing popularity Of sports, stadium fields are receiving a rising demand to accommodate multiple teams and sports, dramatically increasing usage. This results in difficult and costly maintenance in order to ensure the field provides adequate aesthetic, performance and safety characteristics. The maintenance can also prove to be difficult, if not impossible, in harsh climates that involve cold weather and excessive rain. Indoor natural grass fields are possible, but the costs are not practical for most venues. These limitations of natural grass led tO the creation of synthetic surfaces with the intention Of providing superior performance characteristics while reducing maintenance costs. The first artificial surface was invented in the 19608 (US. patent #3332828) under the name “Chemgrass”. The product emerged into national attention with its installation in the Houston Astrodome in 1966, and was subsequently renamed “AstroTurf”. The original product was more like a carpet surface intended to resemble grass, rather than a surface intended to mimic the performance of natural grass. AstroTurf was later installed in an outdoor stadium at Indiana State University in 1967, further solidifying its role as a natural grass alternative. Many competitors entered the market with similar products including TartanTurf, Omniturf, SuperTurf, ClubTurf, PolyTurf, and InstantTurf. Since its introduction, numerous research projects have been conducted that examine the epidemiology of injury on this first-generation, artificial surface. Bramwell et al. (1972) and Powell and Schootman (1992; 1993) published studies that document significantly higher injury rates during sporting events played on artificial surfaces in comparison to natural grass. Other researchers constructed devices to measure the rotational traction of artificial surfaces in comparison to natural grass. Bonstingl et al. (1975), Cawley et al. (2003), and Livesay et al. (2006) conclude that AstroTurf (The Monsanto Company, St. Louis, MO) yields higher torque than natural grass. Similar studies have examined the influence Of cleated footwear on rotational traction and injury rates. Torg et al. (1974) and Larnbson et al. (1996) conducted epidemiology studies of high school football and noted the shoe worn during an injury. The authors also measured the rotational traction of the various shoe models being worn by the high school teams in the respective year Of their epidemiology study. Both studies conclude that the shoe design with the highest rotational traction yielded significantly higher injury rates. The results of the shoe and surface testing has led to the belief that higher rotational traction is an indicator of elevated injury risk. In the late 19803, a second-generation of artificial surface was introduced with an infill layer of sand. These surfaces were unsuccessful in American football due to their inherent hardness, erratic traction and abrasiveness. The 19905 resulted in the launch Of yet another artificial surface, this time with a soft absorbent infill material (Often crushed rubber or a combination Of crushed rubber and sand) and longer, more durable pile fibers. This surface is often called the third-generation, artificial surface and is claimed to better simulate a natural grass field. Since its introduction, there is paucity of research regarding the effects of playing on this generation of artificial playing surface, yet they continue to grow in popularity and represent an increasing number Of surfaces in football. To date, there has not been a published epidemiology study that compares injury rates between the third-generation, artificial surface and natural grass. The rotational traction of FieldTurf and AstroPlay, the two most popular third-generation surfaces, has only been documented in one published study conducted with a limited testing methodology (Livesay et al., 2006). The impact that variable components, such as infill material and fiber structure, have on rotational traction is unknown. In the field of sports medicine there is not a well established injury risk criterion by which to judge shoe and surface designs. Torg et al. (1974) assigned football shoe designs a “safety” ranking. The level Of “safety” was determined from an epidemiology study of Philadelphia high school football that noted the frequency of knee injuries associated with particular cleat designs. The shoe designs were then subjected to rotational traction testing and the magnitude of the shoe-surface interface release coefficient was related to a particular safety ranking. This was intended to identify future dangerous football shoes based solely on mechanical traction measurements. This analysis is more than thirty years Old and is not considered applicable to the current state of American football and modern shoe-surface interactions. The best way to determine injury risk in sports may be through the development of biofidelic surrogates that can simulate physiological loading conditions. Similar devices, such as crash test dummies, are Often used by the automobile industry to assess injury risk during a vehicular collision (Forrnan et al., 2006; McDonald et al., 2003; Tornvall et al., 2007). Crash test dummies are instrumented to record data about their dynamic behavior during an impact. The loads and displacements are then related to cadaveric studies in order to predict the relative risk of a particular injury. The development of a traction measurement apparatus that mimics the response of the human lower extremity under torsion may allow assessment of the risk of ankle or knee injury given certain shoe-surface interface combinations (V illwock et al., 2009). A portion of this thesis focuses on the risk of ankle injury. Specifically, the risk of ankle injury due to an external rotation mechanism. This mechanism has been noted to induce injury Often requiring a relatively long recovery time (Boytim et al., 1991; Ebraheim et al., 2003; Miller et al., 1995; Williams et al., 2007). In contrast to the soft tissue injuries reported in many clinical studies on the ankle (Boytim et al., 1991; Edwards and DeLee, 1984; Hopkinson et al., 1990), cadaveric experimental studies have typically generated a high frequency Of bone fi'actures when the foot is externally rotated (Lauge-Hansen, 1950; Markolf et al., 1989; Schaffer and Manoli, 1987; Stiehl et al., 1992). In a majority of manuscripts that describe external rotation injuries of the ankle joint, the age and gender Of the cadaveric test specimens have not been reported (Hirsch and Lewis, 1965; Markolf et al., 1989; Schaffer and Manoli, 1987). These variables may substantially affect both the failure load and the mode of failure to the joint. Most ankle sprains occur in persons under the age of 35 years (Nilsson, 1983). A younger specimen population may result in a high frequency Of ligamentous injtuies, prior to bone fiacture, during excessive levels Of external rotation Of the foot/ankle complex. Measurement Of the rotational moments and angular rotations required to induce soft tissue injury may then be used to develop a biofidelic ankle surrogate that can be used for the evaluation of athletic shoe-surface interfaces and their risk of ankle injury. The research in this thesis includes the mechanical evaluation Of surface and shoe designs as well as the biomechanical analyses Of ankle injury risk from cadaveric tests. Chapter Two describes the rotational traction measurements performed across ten football shoes and four current football playing surfaces. Chapter Three details rotational traction on third-generation, artificial surfaces by examining nine playing surfaces composed of various infill and fiber structures. Chapter Four examines the external rotation mechanism of ankle injury. The influence of foot constraint on injury location is examined, and the torque and rotation required to produce ankle injury is presented. These data were then used to establish a more biofidelic ankle used in the rotational traction apparatus. Chapter Five discusses the design of the surrogate ankle. This chapter outlines the biofidelic attributes of the ankle and how it may ultimately have relevance in establishing an ankle injury risk criterion for new football cleat and surface designs. Lastly, Chapter Six provides conclusions of this study and outlines recommendations for future work. The data fiom the proposed research will make a significant contribution to the understanding Of rotational traction created by the football shoe-surface interface. In conjunction with epidemiological studies, this research will aide in developing future lower leg injury risk criteria. The cadaver ankle experiments in combination with the biofidelic ankle may also be used to assess the risk Of ankle injury from future shoe- surface interface designs. REFERENCES Adrian M and Xu D. (1990) Matching the playing field to the player. In Natural and Artificial Playing Fields: Characteristics and Safety Features. ASTM STP 1073. Schmidt RC, Hoemer EF, Milner EM, Morehouse CA, Eds. American Society for Testing and Materials. pp. 10-19. Bonstingl RW, Morehouse CA, Niebel BW. (1975) Torques developed by different types of shoes on various playing surfaces. Med Sci Sports. 7(2):]27-131. Boytim M], Fischer DA, Neumann L. (1991) Syndesmotic ankle sprains. Am J Sports Med. 19(3):294-298. Brarnwell ST, Requa RK, Garrick JE. (1972) High school football injuries: a pilot comparison Of playing surfaces. Med Sci Sports. 4(3):l66-169. Cawley PW, Heidt RS Jr., Scranton PE Jr., Losse GM, Howard ME. (2003) Physiologic axial load, fiictional resistance, and the football shoe-surface interface. Foot Ankle Int. 24(7):551-556. Ebraheim NA, Elgafy H, Padanilam T. (2003) Syndesmotic disruption in low fibular fractures associated with deltoid ligament injury. Clin Orthop Relat Res. 409:260-267. Edwards GS, DeLee JC. (1984) Ankle diastasis without fiacture. Foot Ankle. 4(6):305- 312. Fernandez WG, Yard EE, Comstock RD. (2007) Epidemiology of lower extremity injuries among US. high school athletes. Acad Emerg Med. 14(7):641-645. Forman J, Lessley D, Shaw CG, Evans J, Kent R, Rouhana SW, Prasad P. (2006) Thoracic response of belted PMHS, the Hybrid III, and the THOR-NT mid-sized male surrogates in low speed, fiontal crashes. Stapp Car Crash J. 50:191-215. Gorham PM, Orofino TA. (1996) Actual field performance of synthetic turf as measured over a thirty year period. In Safety in American Football. ASTM STP 1305. Hoemer EF, Ed. American Society for Testing and Materials. pp. 123-131. Guise ER. (1976) Rotational ligamentous injuries to the ankle in football. Am J Sports Med. 4(1):1-6. Harper JC 11, Morehouse CA, Waddington DV, Buckley WE. (1984) Turf management, athletic-field conditions, and injuries in high school football. Agric Exp Stn. Prog Rep 384. The Pennsylvania State University, University Park, PA. Henderson RL, Waddington DV, Morehouse CA. (1990) Laboratory measurements of impact absorption on turfgrass and soil surfaces. In Natural and Artificial Playing Fields: Characteristics and Safety Features. ASTM STP 1073. Schmidt RC, Hoemer EF, Milner EM, Morehouse CA, Eds. American Society for Testing and Materials. pp. 127-135. Hirsch C, Lewis J. (1965) Experimental ankle joint fractures. Acta Orthop Scand. 36:408- 417. Hopkinson WJ, St. Pierre P, Ryan JB, Wheeler JH. (1990) Syndesmosis sprains of the ankle. Foot Ankle. 10(6):325-330. Lauge-Hansen N. (1950) Fractures of the Ankle II. Combined Experimental-Surgical and Experimental-Roentgenologic Investigations. Arch Surg. 60:957-985. Livesay GA, Reda DR, Nauman EA. (2006) Peak torque and rotational stiffness developed at the shoe-surface interface. Am J Sports Med. 34(3):415-422. Markolf KL, Schmalzried TP, Ferkel RD. (1989) Torsional strength of the ankle in vitro. The supination-external-rotation injury. Clin Orthop Relat Res. 246:266-272. McDonald JP, Shams T, Rangarajan N, Beach D, Huang T, Freemire J, Artis M, Wang Y, Haffner M. (2003) Design and development of a THOR based female crash test dummy. Stapp Car Crash J. 47:551-570. McNitt AS, Waddington DV, Middour R0. (1996) Traction measurement on natural turf. In Safety in American Football. ASTM STP 1305. Hoemer EF, Ed. American Society for Testing and Materials. pp. 145-155. Miller CD, Shelton WR, Barrett GR, Savoie FH, Dukes AD. (1995) Deltoid and syndesmosis ligament injury of the ankle without fracture. Am J Sports Med. 23(6):746- 750. Nilsson S. (1983) Sprains of the lateral ankle ligaments, part II: epidemiological and clinical study with special reference to different forms Of conservative treatment. J Oslo City Hosp. 33(2-3):13-36. Powell JW, Schootman M. (1992) A multivariate risk analysis Of selected playing surfaces in the National Football League: 1980-1989. An epidemiological study of knee injuries. Am J Sports Med. 20(6):686-694. Powell JW, Schootman M. (1993) A multivariate risk analysis of natural grass and AstroTurf playing surfaces in the National Football League 1980-1989. Int Turfgrass Soc Res J. 23:201-211. Rogers JN, Waddington DV. (1992) Impact absorption characteristics on turf and soil surfaces. Agron J. 84:203-209. Schaffer JJ, Manoli A. (1987) The Antiglide Plate for Distal Fibular Fixation. J Bone Joint Surg Am. 69-A(4):596-604. Stiehl JB, Skrade DA, Johnson RP. (Dec, 1992) Experimentally produced ankle fractures in autopsy specimens. Clin Orthop Relat Res. 285:244-249. Torg J S, Quedenfeld TC, Landau S. (1974) The shoe-surface interface and its relationship to football knee injuries. J Sports Med. 2(5):261-269. Tomvall FV, Holmqvist K, Davidsson J, Svensson MY, Haland Y, Ohm H. (2007) A new THOR shoulder design: a comparison with volunteers, the Hybrid III, and THOR NT. Traffic Inj Prev. 8(2):205-215. Villwock MR, Meyer EG, Powell JP, Fouty AJ, Haut RC. (2009) Football playing surface and shoe design affect rotational traction. Am J Sports Med. 37(3):518-525. Williams GN, Jones MH, Amendola A. (2007) Syndesmotic ankle sprains in athletes. Am J Sports Med. 35(7):]197-1207. Chapter 2: Football Playing Surface and Shoe Design Affect Rotational Traction ABSTRACT: High rotational traction between football shoes and the playing surface may be a potential mechanism Of injury for the lower extremity. A mobile testing apparatus with a compliant ankle was used to apply rotations and measure the torque at the shoe-surface interface. The mechanical surrogate was used to compare five football cleat patterns (total Of ten shoe models) and four football surfaces (FieldTurf, AstroPlay, and 2 natural grass systems) on site at actual surface installations. Both artificial surfaces yielded significantly higher peak torque and rotational stiffness than the natural grass surfaces. The only cleat pattern that produced a peak torque significantly different than all others was the turf-style cleat, and it yielded the lowest torque. The model of shoe had a significant effect on rotational stiffness. A potential shoe design factor that may influence rotational stiffness is the material(s) used to construct the shoe's upper. As football shoes and surfaces continue to update their designs, new evaluations of their performance must be assessed under simulated loading conditions to ensure that player performance needs are met while minimizing injury risk. 10 INTRODUCTION: Injuries to the lower extremity are among the most fi'equent injuries for all levels Of sports and Often account for more than 50% of reported injuries (Fernandez et al., 2007). In the National Football League (NFL), ankle and knee sprains combine to account for about 20% of all reported injuries (Powell and Schootman, 1992;1993). These injuries can occur during contact between players or in noncontact situations, such as a rapid change in direction or with a combination of high compressive load and twist during a jump landing (Arnold et al., 1979; Fauno and Wulff, 2004). Frequently the mechanism of injury involves a foot planted on the playing surface with an excessive internal rotation Of the upper body (Guise, 1976). Traction is defined by the ASTM committee on Sports Equipment and Facilities to be the resistance to relative motion between a shoe outsole and a sports surface, which does not necessarily Obey classical (Coulomb) laws of friction (ASTM F2333, 2006). While linear traction is necessary for hi gh-level performance during any athletic contest (Shorten et al., 2003), it is generally accepted that excessive rotational traction may precipitate ankle and knee injuries (Bonstingl et al., 1975; Lambson et al., 1996; Nigg and Yeadon, 1987; Torg et al., 1974). A previous study Of ACL injuries in high school football players documented a significant relationship between cleat design, the amount Of rotational traction and the risk of ACL injury on grass (Larnbson et al., 1996). The “edge” cleat design produced significantly higher rotational traction and was associated with an ACL injury rate 3.4 times higher than that Of all other designs combined. Other studies have noted differences Of injury rate in the presence or absence of specific risk factors, such as whether the surface was natural grass or AstroTurf. These 11 differences in injury rate may be due to variations in the structure and materials of the turfs (Hammer, 1981), the running speed Of the players (Stanitski et al., 1974), or the coefficient of fiiction between the surface and shoe (Andreasson et al., 1986). The injury risk factor may also depend on the player’s position and the type of play at the time Of injury, both Of which would influence loading mechanisms on the lower extremity (Powell and Schootman, 1992). Although rotational traction has been documented in previous studies (usually as the peak torque magnitude recorded during dynamic testing) for numerous shoe-surface interfaces, most testing devices are not portable and therefore cannot be used to test the actual playing surfaces (Bonstingl et al., 1975; Cawley et al., 2003; Larnbson et al., 1996; Torg et al., 1974). The aforementioned studies also have not evaluated the types of synthetic surfaces currently used in professional, college and high school football. The modern synthetic surface is a sharp contrast to the dense and abrasive turfs that were introduced in the 1960S. Artificial surfaces now consist of longer, more grass-like fibers that are surrounded and stabilized by infill materials, such as rubber and sand. A more recent study measured the peak torque and rotational stiffness developed at the shoe- surface interface of three infill systems with a portable testing device (Livesay et al., 2006). The limitations of that study were the small compressive normal force and the use Of only the forefoot cleats rigidly mounted on a plate. Rotational stiffness (defined as the slope of the torque versus rotation data in a predefined angular range) was identified as a more sensitive indicator Of the mechanical interaction between different shoe-surface combinations than the peak torque (Livesay et al., 2006). 12 There are limited data with regards to the rotational traction Of cleated football shoes on modern third-generation, artificial surfaces. The purpose Of the present study was to investigate the rotational shoe-surface interactions using a variety of shoes and surfaces currently employed in football by means of a mobile testing apparatus constructed with a surrogate lower leg. The first hypothesis of the study was that shoe designs with numerous and or large cleats around the peripheral margin of the sole would exhibit higher rotational traction than shoes with fewer or smaller cleats on the peripheral margins. The second hypothesis was that manufacturer and material variation between shoe models would result in rotational traction differences among shoe models within cleat pattern groups. The third hypothesis was that an artificial surface that allows greater infill contact with the cleat will produce higher rotational traction than natural grass and similar artificial surfaces which limit infill contact with the cleat. A better understanding of the interaction between current shoe-surface interfaces will provide athletic teams with information on the rotational traction Of various shoe-surface combinations. These data may ultimately have relevance to the risk potential for rotational lower leg injuries on various shoe-surface interface combinations. MATERIALS AND METHODS: Four different surfaces were evaluated in this study: 1) an artificial surface with an infill composed of a sand/rubber blend (FieldTurf, FieldTurf Tarkett, Montreal, Quebec, Canada), 2) an artificial surface with a 100% rubber infill (AstroPlay, Southwest Recreational Industries, Inc., Leander, Texas), 3) natural grass composed of Kentucky bluegrass and a small percentage of ryegrass in combination with a native Michigan soil, l3 4) natural grass composed of Kentucky bluegrass and a small percentage of ryegrass in combination with a custom soil engineered for strength and drainage that consisted of 90% sand and 10% silt and clay. The FieldTurf system was the playing surface used in an indoor sports complex, and it was installed seven years prior to testing. The AstroPlay system was also the playing surface used in an indoor sports complex, and it was installed five years prior to testing. Both natural grass plots were part of outdoor football fields with full-time maintenance staff. The FieldTurf was composed of parallel slit polyethylene fibers with an approximate 50/50 combination of layered silica sand and cryogenically processed crumb styrene-butadiene rubber (SBR) infill (F ieldTurf.com, 2008), with a primary top layer of cryogenic rubber. The fiber layout of FieldTurf is constructed with a gauge length Of 3/ ”. This measurement refers to the distance between rows of fiber tufts. The AstroPlay was composed of parallel slit polyethylene fibers constructed with a 3/8” gauge length and with an all cryogenically processed SBR crumb infill (SRISports.com, 2008). Each surface was tested using ten different shoes (Table 2.1), yielding 40 different shoe-surface combinations. The shoes were grouped into five categories based on design properties: 1) cleated shoes with seven removable cleats, five covering the forefoot of the sole and two covering the heel region (7 Studded), 2) molded cleat shoes with twelve cleats around the perimeter of the sole, eight around the forefoot and four around the heel region (12 Studded), 3) molded cleat shoes with four cleats around the heel region and at least fifteen cleats distributed across the forefoot region (Hybrid), 4) cleat designs characterized by blade style cleats (Edge), 5) shoes which had a dense pattern of short elastomeric cleats distributed over the entire sole (Turf). 14 Table 2.1: Description Of tested football shoes Max Cleat Number Cleat Category Ml“ Model HeIght material of cleats length (mm) . Mid- . NIke BladellTD Elastomenc 14 16.3 12 cut Studded Adidas 8‘30““ L0” TPU 13 12.5 Fly cut . Vapor Jet Low- NIke TD cut TPU 12 12.0 Edge . Scorch Low- AdIdas TRX cut TPU 15 13.0 . Comer Mid- . AdIdas Blitz'iMD cut Elastomenc 15 11.0 Air Zoom Mi d- Nike Superbad ut Elastomeric 21 11.0 Hybrid FT ° Adidas Gridlron mt" Elastomeric 20 12.0 . AirZoom Mid- TPU 7 we BladeD cut (SteelTIp) 7 12‘5 Studded . Ouickslant Mid- TPU AdIdas D. cut (SteelTIp) 7 12.5 Turf Adidas Turf Hog M'd' Elastomeric 88 6.5 LE cut Due to the mechanical interpenetration of the cleats and playing surface, as well as properties of the materials themselves, rotational traction is dependent on many factors which require that the measurements be made at loads and rates Of loading that are expected to occur in vivo (ASTM F2333, 2006). A testing apparatus was developed to 15 simulate the anthropomorphic data of a 95th percentile male (Robbins, 1985). This included matching the compressive load to 1 x body weight (1000 N) and fabricating the surrogate lower leg with a tibia length Of 44 cm (Robbins, 1985). In addition to reproducing key mass and length measurements for the surrogate leg, the ankle was designed to be compliant with regards to internal/extemal rotation by means Of a deformable elastomeric washer at this location. The testing apparatus (Figure 2.1) was designed to apply a dynamic rotation and measure the torque produced at the shoe/ surface interface. The apparatus was fabricated to conform to an international standard method for measuring rotational traction characteristics Of an athletic shoe-surface interface (ASTM F2333, 2006). The device consisted of an aluminum frame that could be raised and lowered to the ground with wheels to allow for easy mobility. The frame supported the surrogate lower limb, a suspended 425 N weight and a 0.25 m radius gear that were used to produce a torque on the shoe. The weights were released by means Of a manual lever arm located on the side of the testing device. The drop height of the weight hanger was adjusted so that the input rotation angle of the shaft was 90 degrees. The rate of rotation was approximately 180 degrees per second, which exceeds the minimum of 45 degrees per second required by the ASTM testing standard (ASTM F2333, 2006). The frame was stabilized on the test surfaces by two operators standing on outboard platforms. 16 Input Rotary Encoder W3. | Surrogate Lower Leg ,h. ...}; Dynamic Normal Force Compressive Weights 5.} lntemal (Normal Force) — Leg Rotation _ Torsion Drop Weights Release --':21-e:: Torsion Pulley Deformable {.._-g: Elastomer Biaxial Load Cell — | for Compliant Ankle Rotary Ankle Football Shoe Mounted on a Operator /_. Rigid Foot Model Standing _ g. ,- Platform Remov .le Resultant External Torque at Wheels the Shoe-Surface Interface Figure 2.1: Description Of rotational traction testing apparatus To better represent a worst-case injury situation, the current study replicated a loading condition having full cleat contact with the ground. The peak torque measured in tests with full cleat contact has been shown to be typically 70% higher than tests with only forefoot cleats (Bonstingl et al., 1975). A rigid model of the right foot was fabricated and attached below the ankle position on the testing device. The foot represented a US. size 13 shoe and the center of rotation (COR) on the test device was adjustable. For all tests documented in this report, the COR was set at the midfoot, a distance of 14 cm from the heel. The device generated a dynamic internal rotation of the leg, resulting" in an externally directed ground reactionary torque on the foot. A torsional load cell (Model 1216CEW-2K, Interface, Scottsdale, AZ) calibrated for 170 Nm full-scale capacity was 17 placed below the gear and connected tO the lower leg shaft in order to record torque. In addition, two angular displacement transducers (Model 0605-S7104010201, Trans-Tek Inc., Ellington, CT) were used to record the rotation of the lower limb segments. The first transducer measured total rotation of the leg and was located above the compressive weights. The second was placed inside the artificial leg to measure the relative rotation at the ankle (between the foot and shaft). The difference between leg and ankle rotation provided the shoe rotation relative to the ground. The data were processed through a strain gage amplifier (Model 3318-00, Analog Devices, Inc., Norwood, MA) connected to an A2D card (Model PC-Card-DASI6/ 16, Measurement Computing Corp., Norton, MA) and recorded on a laptop computer (N Series Lifebook, Fujitsu, Japan). A custom program was written in LabView (Version 7.0, National Instruments, Austin, TX) for data collection. Data were collected for 5 seconds at 1000 Hz and the recorded data fi'om each trial consisted of 100 ms before and 900 ms after a torque threshold Of 3 Nm was reached in the test. Five trials were performed for each shoe-surface combination. The testing apparatus was repositioned between trials to a new adjacent section of turf. The air temperature was also recorded for each day Of testing. Data from all trials were analyzed to determine the peak torque. Plots were created to document the change in torque relative to the degree of shoe rotation allowing for the calculation Of rotational stiffness. In the current study, we found that the shoe upper could flex under the applied torque and rotate about the mid foot axis as the edge Of the shoe plowed through the surface. Therefore, a calculation of rotational stiffness between fixed angles, as used by Livesay et al. (2006), was not advisable. It was 18 necessary to compute the stiffness between two predetermined levels of torque for all shoe-surface interfaces. The chosen interval was from the start Of the test, identified by 3 Nm of torque, to 75% of the peak torque generated for each particular test. The average peak torque and rotational stiffness of the five trials was used for subsequent statistical analyses. A two way ANOVA, surface (n=4) by shoe model (n=10), was conducted in SigmaStat (Version 2.03, SPSS Inc., Chicago, IL) to assess the effect of surface and shoe on the peak torque and rotational stiffness. Tukey post-hoc tests were performed when indicated. The effect of cleat pattern (n=5) was assessed by a one way AN OVA with Tukey post-hoc tests, when appropriate. Statistical significance was set at p < 0.05 in all analyses. RESULTS: Torque and rotational data were collected on each of the 40 shoe-surface combinations. The shoe was tested with full cleat contact on the ground and a compressive load of 1000N. The plots Of torque versus relative rotation of the shoe were analyzed (Figure 2.2) and several distinct regions were noted: 1) the initial breakaway region, typified by the buildup of torque to begin rotation, 2) a period of increasing torque as the shoe continued to rotate, 3) a period of relatively constant torque which was attributed to slippage between the shoe and surface and 4) a period of unloading at the end of the test. The typical plot consisted of all four regions (Figure 2.2A). If the leading edge of a shoe was twisted and appeared to plow into the surface, as was the case of shoes with relatively pliable uppers (7Fly, Superbad, TRX, and Vapor), Often only three regions were noted by the omission of a distinct slippage region (Figure 2.28). 19 Graph A Torque (Nm) 0 20 40 60 80 Rotatlon (degrees) Figure 2.2A: The representative shape of the torque vs. shoe rotation plot that consisted of forn' regions (initial breakaway, build-up, slippage, unloading). The percent of rotation that occurred in each region was dependent on the shoe-surface combination and varied between shoes and surfaces. 80 Rotation (degrees) Figure 2.2B: The representative shape of the torque vs. shoe rotation plot that consisted Of three regions (omission of slippage). 20 All natural grass testing was conducted in Michigan in early autumn at approximately the midseason of football. NO testing was performed if moisture or a previous rain was noted. The air temperature when testing the surfaces varied during this series of experiments. The artificial surfaces were tested at an air temperature Of 21°C, the grass with sand based soil was tested at 11°C and the grass with native Michigan soil was tested at 32°C. Cleat Pattern The classification of shoe groups did not yield any relationships between cleat pattern and rotational stiffness (Table 2.2). Significant differences in peak torque were only noted with comparison to the Turf cleat (Table 2.3). The Turf cleat produced significantly lower torque than all other groups (p < 0.001). There were no significant differences between the 12 Studded, Edge, Hybrid, and 7 Studded cleat pattern groups. 21 3.3 6.3 6.3 3.3 3.3 :3 6.3 3.3 6.3 8.3 25: 3 an ed en 3 an em a.» em an 8.3 :3 :3 :3 33 a3 :3 83 83 83 a3 .3» eéaz «N «N ma 2 ea 3 «a 3 ca 3. 5 820 3.3 83 63 $3 33 a3 a3 a3 33 33 3.3 .988 team «.u 3 3 em 3 5 3 3. ma 3 «N 82o 3.3 :3 33 :3 $3 :3 83 a3 83 33 33 452.2 a 3.. an em 2.. me «a 3 we em 3 «e 3.3 83 a3 33 3% 83 $3 83 33 a3 83 takes: a en 3 I” 3 3 em 3 3m 3. 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The model of shoe did significantly affect rotational stiffiiess (Tables 2.2 and 2.4). The Adidas Blitz produced significantly higher rotational stiffness than six other models. This was likely attributable to its large rubber cleats, and perhaps more importantly, relatively rigid upper and sole. By comparison, the shoe that produced a rotational stiffness significantly lower than five other models, the Nike Superbad, had a relatively pliable upper and sole, making it more capable of rotating on the rigid footfonn. This allowed the medial edge of the shoe to dig into the ground and continually add rotational traction after breakaway (the initial release of the shoe fiom the surface). 24 - 888 888 88 88 888.8 83 888 8:88 888 88:8: 888 - 83 888 888 8:88 888 83 83 :88 880 888 83 - :88 :88 888 888 83 83 83 8888 828 88 ~88 - :88v 8:8 :28 888 8:8 E8 82:88 888 R88 :88 :88v - :88v ::8 :88 888 828 8388 ~88 8:88 888 8:8 :88v - 888 _88 :88 «:88 N88 83 888 888 :28 :38 888 - 888 888 83 88: 888 83 83 :88 888 :88 888 - 83 :88 88> 8:88 83 83 8:8 888 :88 888 83 - 83 :8: 888 :88 83 E8 838 8:88 83 :88 83 - 8888 88:8: 880 8888 8885 8388 N88 80:. 88> 88: 8888 8.888 038 808383 88.8988 83.808 8% 88383: saw 835. 25 m The values of peak torque and rotational stiffness were significantly affected by the playing surface (Tables 2.3 and 2.4). Both artificial surfaces produced higher torques (p < 0.001) than natural grass surfaces. The natural grass surface with engineered, sand based soil produced higher torques (p = 0.008) than natural grass with native Michigan soil. The rotational stiffness for both artifical surfaces was higher (p < 0.001) than each of the natural grass surfaces. The stiffness of the different systems of artificial or natural grasses was not statistically different from one another. DISCUSSION: High rotational traction between football shoes and playing surfaces may yield a potential for injury to the lower extremity (Bonstingl et al., 1975; Lambson et al., 1996; Nigg and Yeadon, 1987; Torg et al., 1974). The current study utilized a mobile apparatus to record the torque and relative rotation at the shoe-surface interface for a variety of currently available, cleated football shoes in combination with synthetic infill surface systems and natural grasses. A wide variation in peak torques between shoe-surface interfaces was not unexpected, based on the current literature. A previous study by Cawley et al. (2003) shows a torque range of 50 and 120 Nm for 7 studded and turf shoe designs on grass. The trend in peak torque across surfaces was also noted to be similar to a previous study by Livesay et al. (2006) that examines several infill surfaces using a lower compressive load and forefoot cleats rigidly mounted to a circular plate. Although those results could not be directly related to the current data, in both studies the grass surfaces produce the lowest peak torques. 26 The classification of shoe groups based on cleat pattern did not predeterrnine a shoe’s rotational traction characteristics. The only cleat pattern designation that produced peak torques significantly different than all other groups was the turf style cleat. The short elastomeric cleats may not have penetrated the infill layer or soil as deeply as the other models to help limit the degree of rotational traction. The wide range of torques noted both within and across shoe groups emphasized the impact of other factors, beyond cleat pattern, that may affect rotational traction. Therefore, the first hypothesis that related rotational traction to cleat pattern could not be validated in the current study. The second hypothesis that related rotational traction to shoe model was validated with regards to rotational stiffness. The shoe shape, upper material, and construction may all be possible contributors to the varying amounts of rotational stiffness. One potential limitation of the present study was the surrogate ankle. The deformable elastomer used to represent the torsional stiffness of the ankle joint averaged 11 Nm/deg, exceeding in vivo measurements of 1.2 Nm/deg by Mote and Lee (1982). However, the in viva stiffness recorded in the previous study was limited to amplitudes of 86 degrees, a significant limitation in the overall response of the joint. Assuming the in vivo stiffness of the ankle joint can be modeled by a bilinear response similar to the knee joint (Dorius and Hull, 1984), the secondary stiffness of the ankle may be on the order of 3 to 5 times the primary stiffness, yielding a maximum torsional stiffness of 6 Nm/deg for the ankle. The surrogate ankle may also be improved by the incorporation of additional degrees of freedom that may alter loading mechanisms on a surface. Inversion/eversion of the ankle may increase the medial edge loading mechanism and dorsiflexion/plantarflexion may effect the load distribution across the cleats. 27 Incorporation of these designs into a surrogate ankle may help to generate more physiological responses of the lower leg at the shoe-surface interface. The artificial surfaces were tested at similar temperatures, while the air temperature for the natural grass testing varied by 21°C. A previous study showed that an increase in air and turf temperature did have an effect on the shoe-surface traction for AstroTurf (Torg et al., 1996). In an extensive literature search, no evidence was gathered regarding a relationship between the ambient air temperature and its effect on traction for a natural grass system. The effect of climate on natural grass systems has been considered in epidemiological studies involving the frequency of injury and the time of season (Orchard, 2002). In a rugby study it was concluded that there was a bias towards a higher frequency of injury in the summer months which was proportionately greater for backs, the players who tend to sustain most non-contact injuries (Gissane et al., 1998). A major contributor to this bias was believed to be ground hardness, brought about by drier and warmer conditions in the summer season. Both natural grass systems in the present study were tested in the same autumn month, and they were regularly watered. A potential threshold for a “safe” torsional release coefficient of shoes and surfaces was introduced in the 19705 (Torg et al., 1974). In the current study a normal force of 1000 N would generate a theoretical “safe” torque of approximately 95 Nm, based on the previous study results. Most shoe-surface interface values in the current study exceeded this threshold level. This level also exceeds the maximum torque that the ankle can support, approximately 75 Nm, based on cadaver tests (Hirsch and Lewis, 1965). On the other hand, Shoemaker et a1. (1988) suggest that muscles may contribute 28 as much as 70 Nm of resistive torque and help protect the lower extremity from injury during controlled athletic maneuvers. It is unknown if differences in rotational stiffness at the shoe-surface interface might impact the risk of injury, as suggested in the Livesay et al. (2006) study. The lower rotational stiffness observed for both natural grass systems compared to the artificial surfaces indicated a lower rate of loading. This might allow more time for a protective type of neuromuscular control in the lower extremity that could help stabilize the ankle and knee joints during cutting maneuvers (Livesay et al., 2006). The differences in rotational stiffness across shoes may also influence injury risk. A potential design factor may be the materials used to construct the shoe’s upper. A shoe with a pliable upper may allow more time for neuromuscular control, but it may also allow the foot to pronate while the leg is internally rotated. This loading scenario may result in rupture of the anterior tibiofibular ligament, a severe time loss injury (Guise, 1976). Future epidemiological studies of shoe and surface injury rates on infill based surfaces and grass will be important in generating the “real” injury risk for various shoe-surface interfaces. In conclusion, an extensive amount of work exists concerning the interaction of football cleats with the first-generation of non-infill AstroTurf, yet much remains unknown about the performance characteristics of modern infill, artificial surfaces. The present study investigated the dynamic performance of a number of currently used football shoes and cleat designs on natural grass and infill based artificial surfaces under a compressive load that may be representative of a 95th percentile male during a sports activity. It is important to continue to gain an understanding of the tractional 29 characteristics of the shoe-surface interface as manufacturers continue to update cleat and surface designs. In order to meet the critical need of improving the design of shoe- surface interfaces many areas still need further research. The effects of moisture and temperature on traction characteristics of infill based artificial surfaces need additional study. It is also unknown whether an internally directed ground reaction torque would engage the cleats in a different manner and generate different torque results. Meyer et al. (2008) demonstrate that this type of loading may generate isolated rupture of the anterior cruciate ligament. From a performance aspect, linear traction testing would assess a player’s need for speed and agility (Krahenbuel, 1974; Morehouse and Morrison, 1975). These data could then be used to help improve shoe-surface interfaces and mitigate injury potential while maintaining player performance. 30 REFERENCES American Society for Testing and Materials. (2006) Annual Book of ASTM Standards. Standard test method for traction characteristics of the athletic shoe - sports surface interface. F2333-04. ASTM. 15.0721412-1420. Andreasson G, Lindenberger U, Renstrom P, Peterson L. (1986) Torque developed at simulated sliding between sport shoes and an artificial turf. Am J Sports Med. 14(3):225- 230. Arnold JA, Coker TP, Heaton LM, Park JP, Harris WP. (1979) Natural history of anterior cruciate tears. Am J Sports Med. 7(6):305-313. Bonstingl RW, Morehouse CA, Niebel BW. (1975) Torques developed by different types of shoes on various playing surfaces. Med Sci Sports. 7(2): 127-131. Cawley PW, Heidt RS Jr., Scranton PE Jr., Losse GM, Howard ME. (2003) Physiologic axial load, fiictional resistance, and the football shoe-surface interface. Foot Ankle Int. 24(7):551-556. Dorius LK, Hull ML. (1984) Dynamic simulation of the leg in torsion. J Biomech. l7(l):1-9. Fauno P, Wulff J akobsen B. (2004) Mechanism of anterior cruciate ligament injuries in soccer. Int J Sports Med. 27:75-79. Fernandez WG, Yard EE, Comstock RD. (2007) Epidemiology of lower extremity injuries among US. high school athletes. Acad Emerg Med. 14(7):641-645. F ieldTurf Inc [Internet]. Product Overview. Available at: http://www.fieldturf.com/product/designConstruction.cfrn. Accessed Dec 19, 2007. Gissane C, Jennings D, White J, Cumine A. (1998) Injury in summer rugby league football: the experiences of one club. Br J Sports Med. 32(3):]49-52. Guise ER. (1976) Rotational ligamentous injuries to the ankle in football. Am J Sports Med. 4(1):1-6. Hammer D. (1981) Artificial playing surfaces. Athletic Training. 16:127-129. Hirsch C, Lewis J. (1965) Experimental ankle joint fractures. Acta Orthop Scand. 36:408- 41 7. Krahenbuel GS. (1974) Speed of movement with varying footwear conditions on synthetic turf and natural grass. Res Q. 45:28-33. 31 Lambson RB, Bamhill BS, Higgins RW. (1996) Football cleat design and its effect on anterior cruciate ligament injuries. A three year prospective study. Am J Sports Med. 24(2):]55-159. Livesay GA, Reda DR, Nauman EA. (2006) Peak torque and rotational stiffness developed at the shoe-surface interface. Am J Sports Med. 34(3):415—422. Meyer EG, Baumer TG, Slade JM, Smith WE, Haut RC. (2008) Tibiofemoral contact pressures and osteochondral microtraurna during anterior cruciate ligament rupture due to excessive compressive loading and internal torque of the human knee. Am J Sports Med. 36(10):l966-1977. Morehouse CA, Morrison WE. (1975) The artificial turf story: A research review. Penn State HPER Series. The Pennsylvania State University. University Park. Mote CD Jr, Lee CW. (1982) Identification of human lower extremity dynamics in torsion. J Biomech. 15(3):211-222. Nigg BM, Yeadon MR. (1987) Biomechanical aspects of playing surfaces. J Sports Sci. 5(2):]17-145. Orchard J. (2002) Is there a relationship between ground and climatic conditions and injuries in football? Sports Med. 32(7):419-432. Powell JW, Schootman M. (1992) A multivariate risk analysis of selected playing surfaces in the National Football League: 1980-1989. An epidemiological study of knee injuries. Am J Sports Med. 20(6):686-694. Powell JW, Schootman M. (1993) A multivariate risk analysis of natural grass and AstroTurf playing surfaces in the National Football League 1980-1989. Int Turfgrass Soc Res J. 23:201-211. Robbins D. (1985) Anthropometry of motor vehicle occupants. Volume 3. Transportation Research Institute. DOT/HS 806 717. Shoemaker SC, Markolf KL, Dorey FJ, Zager S, Namba R. (1988, March) Tibial torque generation in a flexed weight-bearing stance. Clin Orthop Relat Res. 228:164-170. Shorten MR, Hudson B, Himmelsbach JA. (2003, July 6-12) Shoe-surface traction of conventional and in-filled synthetic turf football surfaces. In: Milbum, P. (ed.) Proc XIX International Congress of Biomechanics, University of Otago, Dunedin, New Zealand. Dunedin, NZ. International Society of Biomechanics. CD ROM abstracts and proceedings. Southwest Recreational Industries [Internet]. AstroPlay overview. Available at: http://www.srisports.com/field/filled.htm. Accessed Feb 25, 2008. 32 Stanitski CL, McMaster JH, Ferguson RJ. (1974) Synthetic turf and grass: A comparative study. J Sports Med. 2(1):22-26. Torg J S, Quedenfeld TC, Landau S. (1974) The shoe-surface interface and its relationship to football knee injuries. J Sports Med. 2(5):261-269. Torg J S, Stillwell G, Rogers K. (1996) The effect of ambient temperature on the shoe- surface interface release coefficient. Am J Sports Med. 24:79-82. 33 Chapter 3: The Effects of Various Infills, Fiber Structures, and Shoe Designs on Generating Rotational Traction on an Artificial Surface ABSTRACT: The purpose of this study was to investigate the role of infill material and fiber structure on the rotational traction associated with American football shoes on infill- based, third-generation, artificial surfaces. A mobile testing apparatus with a compliant ankle was used to apply rotations and measure the torque produced at the football shoe- surface interface. The mechanical surrogate was used to compare three infill materials in combination with three fiber structures, creating a total of nine unique surfaces. Infill material, fiber structure and shoe design were all found to significantly affect rotational traction. The cryogenically processed, styrene-butadiene rubber infill yielded significantly higher peak torques than the ambient ground, styrene-butadiene rubber and extruded thermoplastic elastomer infills. An artificial surface with a nylon root zone yielded significantly lower peak torques than similar fiber surfaces without a nylon root zone. The size of infill particles and the presence of a nylon root zone may influence the compactness of the infill layer. These features may act to alter the amount of cleat contact with the infill, thereby influencing rotational traction. The amount of cleat contact with the surface may also be determined by the shoe design. 34 INTRODUCTION: The popularity of artificial turf has continued to grow since its first emergence in the 19603. It is now considered by many to be a viable alternative to natural grass, as evidenced by its prevalence in numerous indoor and outdoor stadiums across the world. The latest generation, often termed the “third-generation”, of artificial surfaces was introduced in the 19903. These surfaces are comprised of a soft absorbent infill material (often crushed rubber or a combination of crushed rubber and sand) and longer, more durable pile fibers. This surface is often claimed to better simulate a natural grass field, but since its introduction there is paucity of research regarding the effects of playing on this generation of artificial playing surface. Injuries to the lower extremity are among the most frequent injuries for all levels of sports and often account for more than 50% of reported injuries (Fernandez et al., 2007). In the National Football League (NFL) ankle and knee sprains combine to account for about 20% of all reported injuries (Powell and Schootman, 1992:1993). These injuries can occur during contact between players or in noncontact situations, such as a rapid change in direction or with a combination of high compressive load and twist during a jump landing (Arnold et al., 1979; Fauno and Wulff Jakobsen, 2004). Frequently the mechanism of injury involves a foot planted on the playing surface with an excessive rotation of the upper body (Guise, 1976). Traction is defined by the ASTM (American Society for Testing and Materials) committee on Sports Equipment and Facilities to be the resistance to relative motion between a shoe outsole and a sports surface that does not necessarily obey classical (Coulomb) laws of friction (ASTM F2333, 2006). While linear traction is necessary for 35 high-level performance during any athletic contest (Shorten et al., 2003), it is generally accepted that excessive rotational traction may precipitate ankle and knee injuries (Bonstingl et al., 1975; Lambson et al., 1996; Nigg and Yeadon, 1987; Torg et al., 1974). A previous study of ACL (anterior cruciate ligament) injuries in high school football players documented a significant relationship between cleat design, the amount of rotational traction and the risk of ACL injury on grass (Lambson et al., 1996). The edge cleat design produced significantly higher rotational traction and was associated with an ACL injury rate 3.4 times higher than that of all other designs combined. Other studies have noted differences of injury rate in the presence or absence of specific risk factors, such as whether the surface was natural grass or an artificial surface. These differences in injury rate may be due to variations in the structure and materials of the turfs (Hammer, 1981), the running speed of the players (Stanitski et al., 1974) or the coefficient of fiiction between the surface and shoe (Andreasson et al., 1986). The injury risk factor may also depend on the player’s position and the type of play at the time of injury, both of which could influence the mechanisms of loading on the lower extremity (Powell and Schootman, 1992;1993). Although rotational traction has been documented in previous studies (usually as the peak torque magnitude recorded during dynamic testing), it has been primarily focused on natural grass and the first-generation of short-pile artificial turf (Bonstingl et al., 1975; Cawley et al., 2003; Lambson et al., 1996; Torg et al., 1974). The third- generation, artificial surface used in professional, collegiate and high school sports is a sharp contrast to the dense and abrasive first-generation, artifical turf. Artificial surfaces now consist of longer, more grass-like fibers that are surrounded and stabilized by infill 36 materials, such as rubber and sand. The influence of these individual components on the rotational traction characteristics of an infill artificial surface is unknown. The purpose of the present study was to investigate the influence of infill material and fiber structure on the rotational traction associated with American football shoes on infill based artificial surfaces. The hypothesis of this study was that artificial surfaces with small infill particles and/or a fiber layout that allow greater infill contact with the cleats will produce higher peak torques than surfaces with larger infill particles and/or a fiber layout that limits the infill contact with the cleats. A better understanding of how different components of the artificial surface affect rotational traction may aide in the design of future surfaces. These data may also have relevance to studies on the risk potential for rotational lower leg injuries on current and future surface designs. MATERIALS AND METHODS: Three infill materials were evaluated in this study: A) cryogenically processed, styrene-butadiene rubber (SBR) crumb infill (PermaLife Products, LLC, Guttenberg, New Jersey) (PermaLife.com, 2008), B) ambient ground, SBR crumb infill (PermaLife Products, LLC, Guttenberg, New Jersey) (PermaLife.com, 2008), C) extruded thermoplastic elastomer (TPE) infill (Terra Sports Technology, The Netherlands) (TerraSportsTech.com, 2008). They were tested in combination with three fiber structures: 1) monofilament polyethylene fibers (GarneDay MT, General Sports Venue, LLC, Rochester, Michigan) (AstroTurfUSA.com, 2008), 11) parallel slit polyethylene fibers (GarneDay Xpe, General Sports Venue, LLC, Rochester, Michigan) (AstroTurfUSA.com, 2008), III) monofilarnent polyethylene fibers in conjunction with a 37 nylon root zone (GarneDay 3D, General Sports Venue, LLC, Rochester, Michigan) (AstroTurfUSA.com, 2008). A nylon root zone is a simulated thatch layer at the base of the tufted turf (Figure 3.1). The zone provides fiber support and reduces infill compaction (AstroTurfUSA.com, 2008). All of the fiber structures were constructed with a 3/8” gauge length (the distance between rows of fiber tufts). The nine iterations of artificial turf were installed outdoors with a fulltime maintenance staff and had been in place for approximately one year with limited usage when tested. Figure 3.1: Infills (upper left to right) — A (cryogenic SBR), B (ambient SBR), C (extruded TPE); Fibers (lower left to right) — I (monofilament), 11 (parallel slit), III (monofilarnent with nylon root zone). 38 The relative fineness of each infill was analyzed by a fixed volume comparison. The density of each infill was calculated using a 50 cm3 container and an electronic semi- rrricro balance (Model R160D, Sartorius, Germany). A fixed volume of 0.2 cm3 of each infill was then analyzed using SigrnaScanPro Image Analysis (Version 5.0.0, SPSS Inc., Chicago, IL). The number of particles was recorded, as well as the maximum diameter of each particle. Each surface was tested using ten different shoes, yielding 90 different shoe- surface combinations. The shoes were grouped into five categories, based on design properties (Table 3.1): 1) 7 Studded - traditional cleated shoes with seven removable cleats, five covering the forefoot of the sole and two covering the heel region, 2) 12 Studded - molded cleat shoes with twelve cleats around the perimeter of the sole, eight around the forefoot and four around the heel region, 3) Hybrid - molded cleat shoes with four cleats around the heel region and at least fifteen cleats distributed across the forefoot region, 4) Edge — shoes characterized by blade style cleats, 5) Turf — shoes which had a dense pattern of short elastomeric cleats distributed over the entire sole. 39 Table 3.1: Description of tested football shoes Max Cleat Number Cleat Category Mfr. Model Height material of cleats length (mm) . Mid- . Nike BIadeIITD Elastomeric 14 16.3 12 cut Studded Adidas SCO'CW L0” TPU 13 12.5 Fly cut . Vapor Jet Low- Nike TD cut TPU 12 12.0 Edge . Scorch Low— Adidas TRX cut TPU 15 13.0 . Comer Mid- . Adidas BlitZYMD cut Elastomeric 15 11.0 Air Zoom Mi d- Nike Superbad ut Elastomeric 21 11.0 Hybrid F-'T C Adidas Gridlron :11? Elastomeric 20 12.0 . AirZoom Mid- TPU 7 ””3 BladeD cut (SteelTIp) 7 125 Studded . Ouickslant Mid- TPU Adidas D cut (SteelTip) 7 12.5 Turf Adidas Turf Hog M'd' Elastomeric 88 6.5 LE cut A testing apparatus was developed to apply a dynamic rotation and measure the torque produced at the shoe/surface interface (Figure 3.2). The apparatus was fabricated to conform to an international standard method for measuring rotational traction characteristics of an athletic shoe-surface interface (ASTM F2333, 2006). The device 40 consisted of an aluminum frame that could be raised and lowered to the ground with wheels to allow easy mobility. The flame supported the surrogate lower limb, a suspended 425 N weight attached to a 0.25 m radius gear that was used to produce a torque on the shoe. The weight was released by means of a manual lever arm located on the side of the testing device. The drop height of the weight hanger was adjusted so that the input rotation angle of the shaft was 90°. The rate of rotation was chosen to represent a high speed injury situation. During running, the tibia has been documented to internally rotate at ground contact with speeds between 160 and 180°/second (Bellcharnber and van den Bogert, 2000; McClay and Manal, 1998; Stacoff et al., 2000). To represent an in vivo situation, the rate of rotation was approximately 180°/second. This exceeded the minimum rate of 45°/second required by the ASTM testing standard (ASTM F2333, 2006). The flame was stabilized on the test surfaces by two operators standing on the outboard platforms. The testing apparatus was designed to simulate the anthropomorphic data of a 95th percentile male. This included matching the compressive load to 1 x body weight (1000 N) and fabricating the surrogate lower limb with a tibia length of 44 cm (Robbins, 1985). In addition to reproducing key mass and length measurements for the surrogate lower limb, the ankle was designed to be compliant with regards to intemal/extemal rotation by means of a deformable elastomeric washer. 41 g .. Input Rotary Encoder «a... . 1.. Surrogate Lower L88 . Dynamic Normal Force Compressrve Weights lntemal Leg Rotation _ (Normal Force) —— Torsion Drop Weights Torsion Pulley —L; Deformable .33. Elastomer Biaxial Load Cell — for Compliant Ankle Rotary ‘5': _ Ankle Encoder " ~ Football Shoe I -._. Mounted on a Operator f Rigid Foot Model Standing . ; - ~ " Platform Remov le Resultant External Torque at Wheels the Shoe-Surface Interface Figure 3.2: Description of rotational traction testing apparatus To represent a possible worst-case injury scenario, the current study replicated a loading condition having full cleat contact with the ground. The peak torque measured in tests with full cleat contact has been shown to be typically 70% higher than tests with only toe cleats engaged (Bonstingl et al., 1975). A rigid model of the right foot was fabricated and attached below the ankle position on the testing device. The foot represented a US. size 13 shoe, and the center of rotation (COR) on the test device was adjustable. The COR was set at the midfoot, a distance of 14 cm from the heel for all tests. The device generated a dynamic internal rotation of the leg, resulting in an externally applied ground reactionary torque on the foot. A torsional load cell (Model 1216CEW-2K, Interface, Scottsdale, AZ) calibrated for 170Nm full-scale capacity was 42 placed below the gear and connected to the lower leg shaft in order to record torque. The data was processed through a strain gage amplifier (Model 3B18-00, Analog Devices, Inc., Norwood, MA) connected to an A2D card (Model PC-Card-DAS16/l 6, Measurement Computing Corp., Norton, MA) and recorded on a laptop computer with Windows XP Professional operating system. A custom program was written in LabView (Version 7.0, National Instruments, Austin, TX) for data collection. Data were collected for 5 seconds at 1000 Hz and the recorded data fiom each trial consisted of 100 ms before and 900 ms after a torque threshold of 3 Nm was reached in the test. Five trials were performed for each unique combination of shoe, fiber and infill. The testing apparatus was repositioned to a new adjacent section of the artificial surface between trials. The air temperature was also recorded on each day of testing. Data from all trials were analyzed to determine the peak torque. A two way ANOVA was performed with SigmaStat (Version 2.03, SPSS Inc., Chicago, IL) to assess the effect of infill (n=3) and fiber structure (n=3) on the peak torque, with repeated measures across trials (n=50). When the differences in the mean values among the infill and/or fiber groups were found to be greater than would be expected by chance, Tukey post-hoe tests were performed to detect statistically significant differences between infill (A,B,C) and fiber (I,II,III). The effect of cleat pattern (n=5) was assessed by a one way ANOVA with Tukey post-hoc tests, when appropriate. Statistical significance was set at p < 0.05 for all analyses. 43 RESULTS: The testing apparatus collected torque-time data on the ninety shoe-surface interface combinations (Table 3.2). The value of peak torque was significantly affected by the type of infill and fiber structure. Infill A yielded significantly higher peak torques (p < 0.001) than other infill types (Figure 3.3). There was no statistical difference between infills B and C. Fiber III produced significantly lower peak torques (p < 0.001) than other fiber types (Figure 3.4). There was no statistical difference between fibers I and II. 44 8.3 8.3 8.3 83 8.3 83 83 :3 8.3 :.3 5.82 «.8 _.8 :.8 8.8— 8.8 88— n8: 3: 8.88 88: 83 8.3 8.3 8.3 83 :3 :.3 83 8.3 8.3 :3 o-E 8.8 8.88 8.8 8.8 8.88 8.8 8.88 38 8.888 8.8 8.88 8.3 :3 83 83 :.3 8.3 83 8.3 83 8.3 83 o-= :.8 8.88 8.8 8.8 8.88 38 8.88 8.88 88: 3:8 88: 8.83 8.3 83 8.3 83 :3 8.3 83 83 8.3 8.3 0-8 «.8 8.8: 8.8 38 38 38 8.8 8.88 88: 8:8 8:: .883 8.3 8.3 8.3 :3 :3 8.3 83 83 83 8.3 8-5 8.8 88: 8.8 8.8 8.8 8.8 8.8 88: 8.8 8.8 88: .:83 83 8.3 :3 83 :3 83 83 8.3 :3 8.3 8-: 8.8.. 8.88 8.8 38 8.88 8:8 N888 8.88 88: 8.88 8.3 .883 83 8.3 83 83 83 8.3 83 8.3 83 8.3 8-8 8.88 :8: 8.8 8.8 8.8 8.8 882 8:2 883 3: 883 .883 8.3 8.3 8.3 83 883 8.3 :.3 83 :.3 8.3 <88 «.8— 888 8.8 8:88 8.88 8.8 8.888 8.8: 8.888 8:2 8:: 4883 83 8.3 :.3 83 8.8% 83 8.5 8.3 83 83 <8 :8: 8:8 882 8.8 88: 8.88 883 33 8.3 8.8: 88: 883 83 83 8.3 83 8.3 8.3 8.3 8.3 83 883 <8 88.: 18.: 8.2: :82 8.3 38 8.8: 32 88: 8.8: 883 2482 8E5... .585 8828 88883 83.888 588 5:. 888> .8: 888.8 38.58 8...: 888.88 : 8.588 888 888.8 2 8.8 833.0 83 88.8 .3888 88. 82 i 899 838 ”:8 8.8.: 45 14o '- 130 120 * 110 100 _. Peak Torque (Nm) 80 70 60 lnflll A Infill B Infill C Figure 3.3: Box plot of peak torque across shoes for each infill. The line near the center of the box represents the median value, the box represents the inter-quartile range and the whiskers represent the range. * indicates significant difference compared to other infills. 140 130 120 110 * 100 Peak Torque (Nm) 70 Fiber I Fiber II Fiber III Figure 3.4: Box plot of peak torque across shoes for each fiber. The line near the center of the box represents the median value, the box represents the inter-quartile range and the whiskers represent the range. * indicates significant difference compared to other fibers. 46 The cleat pattern significantly affected peak torque. The 12 Studded and Edge cleat groups yielded the highest peak torques, while the Turf shoe, composed of a dense pattern of short elastomeric cleats, produced the lowest torques (p < 0.001) (Figure 3.5). The peak torques between the Hybrid and 7 Studded cleat groups were not significantly different. 140 130 " 120 ~ ' ~ 110 100 _ 1 0L) Peak Torque (Nm) 70... . .. l 60 12 Studded Edge Hybrid 7 Studded Turf Figure 3.5: Box plot of peak torque across surfaces for each shoe type. The line near the center of the box represents the median value, the box represents the inter-quartile range and the whiskers represent the range. ~ indicates significant difference with respect to Hybrid, 7 Studded, and Turf designs. (2 indicates significant difference with respect to 12 Studded, Edge and Turf designs. A indicates significant difference with respect to all other cleat designs. 47 Size and volume measurements of the three infills were recorded (Table 3.3). All testing was conducted in Michigan in early autumn. No testing was performed if moisture was observed on the surface, or if it had recently rained. The experiments were performed over a one month period, resulting in air temperature variations (Table 3.4). Infill A was tested at an average temperature of 20.4 :I: 3.1°C, infill B at 31.7 :l: 2.1°C and infill C at 26.9 :t 35°C. Fiber I was tested at an average temperature of 24.4 d: 5.9°C, fiber II at 26.1 d: 45°C , and fiber III at 28.4 :l: 5.4°C. Table 3.3: Infill size as measured using particles in a 50 cc container Infill Mean Diameter (m) Number of Particles A 1.73 l 14 B 2.39 73 C 2.40 22 Table 3.4: Air temperature during rotational traction testing — degrees C; mean temperature (SD) Surface Temperature (°C) 1- A 18.6 (1.9) n - A 21.2 (4.6) 111 - A 21.4 (0.7) I- B 31.7 (0.0) II - B 29.8 (0.9) m - B 33.7 (2.1) 1- c 22.9 (2.3) 11 — c 27.4 (0.5) m - c 30.2 (0.5) 48 DISCUSSION: High rotational traction between football shoes and playing surfaces may yield a potential for injury to the lower extremity (Bonstingl et al., 1975; Lambson et al., 1996; Nigg and Yeadon, 1987; Torg et al., 1974). The current study utilized a mobile testing apparatus to record torque at the shoe-surface interface for different combinations of infill material and fiber structure. The torques were measured on each surface using ten different cleated shoes, yielding ninety unique shoe-surface permutations. In the current study peak torques were significantly affected by infill type. The differences in torque may be due to the fineness of the infill, which is determined by the manufacturing process. A finer particle, such as infill A, may develop a relatively compacted structure of infill that leads to more cleat contact and greater rotational traction. In contrast, the rounded cylindrical shape of infill C may not pack as tightly as infill A to limit the degree of rotational traction. There were no statistical differences in peak torque between fibers I and II. This suggested that there was no difference in rotational traction between monofilament and parallel slit fiber systems. The most influential variable in the generation of torque may have been the presence or absence of the nylon root zone. The nylon root zone needed less infill for system stability that may have affected its compactness. This may have limited cleat contact with the infill and provided a less compacted type of infill layer. This may explain the lower peak torques observed with fiber III. The differences in peak torque noted between the cleat patterns illustrated the impact of shoe design on rotational traction. Shoe designs with numerous and/or large cleats around the peripheral margin of the sole (12 Studded and Edge) yielded higher 49 peak torques than shoes with fewer or smaller cleats (Hybrid, 7 Studded, and Turf). The turf design shoe (Tuerog) produced significantly lower torques than all other designs. The short elastomeric cleats may not have penetrated the infill layer as deeply as the other models to help limit the degree of rotational traction. The statistical difference between cleat pattern groups found in this analysis was not apparent in a previous study by the same investigators which utilized the same testing methodology and cleated shoes (V illwock et al., 2009). The previous study (V illwock et al., 2009) involved a rubber infill surface, a rubber/sand infill surface, and two natural grass surfaces. This resulted in an overall standard deviation in peak torque of 19.9 Nm. In the present study all of the artificial surfaces were composed of 100% rubber infill, resulting in an overall standard deviation in peak torque of 12.7 Nm. This may have allowed differences in rotational traction based on cleat pattern to be more statistically apparent. A limitation of the current study was air temperature variation, which occurred as a result of a month required to complete testing. Infill A, which yielded significantly higher torques than infills B and C, was tested at a lower temperature than infills B and C. Fiber III, which yielded significantly lower torques than fibers I and II, was tested at a higher temperature than fibers I and II. It is interesting to note that the infill and fiber types which produced the lowest torques were tested at the highest air temperatures. If air temperature had influenced these results, the resultant effects would seem to be in sharp contrast to a study performed by Torg et a]. (1996) which documents that an increase in air and turf temperature results in an increase of shoe-surface interface traction. The correlation in that previous study was based on soft rubber shoes on AstroTurf No.8, a short pile non-infill surface that is not comparable to the surfaces in 50 this study. Based on this fundamental difference in design, the influence of temperature variation in the current study is unknown. If the rotational traction characteristics of natural grass are the gold standard upon which artificial surfaces should be compared, several of the surfaces in the current study compared well to this standard. The previous study by this group, utilizing the same testing methodology and cleated shoes, recorded an average peak torque on a natural grass surface of 95.9 :1: 18 Nm (V illwock et al., 2009). The artificial surface constructed with fiber III and infill B generated a lower peak torque, averaging 93.9 Nm. All three fiber structures with infill C also produced peak torques within 3 Nm of the natural grass surface. It is unknown if these similarities in peak torque may result in similar injury rates. A threshold for “safe” torsional release coefficients of shoes and surfaces was introduced in the 19705 (T org et al., 1974). In the current study a normal force of 1000 N would correspond to a theoretical “safe” torque of approximately 95 Nm. Most shoe- surface interface values in the current study exceeded this threshold. This threshold level also exceeds the maximum torque that the ankle can support of approximately 75 Nm, based on cadaver tests (Hirsch and Lewis, 1965). On the other hand, Shoemaker et al. (1988) suggests that muscles may contribute as much as 70 Nm of resistive torque and help protect the lower extremity during controlled athletic maneuvers. Future epidemiological studies of surface injury rates on these infill-based, third-generation, artificial surfaces will be important for generating the “real” injury risk. In conclusion, the current study identified several attributes of third-generation, artificial surfaces, such as infill size and the presence of a root zone, which influenced rotational traction. Cleat pattern was also identified as a shoe design factor responsible 51 for affecting rotational traction on third-generation, artificial surfaces. A vast amount of literature exists concerning the interaction of football cleats with natural grass and the first-generation, non-infill AstroTurf systems. Yet much remains unknown about the tractional characteristics of modern infilled artificial surfaces. From a performance aspect, linear traction testing would assess a player’s need for speed and agility. These data could then be used along with rotational traction information to help improve shoe- surface interfaces and mitigate injury potential while maintaining player performance. 52 REFERENCES American Society for Testing and Materials. (2006) Annual Book of ASTM Standards. Standard test method for traction characteristics of the athletic shoe - sports surface interface. F2333-04. ASTM. 15.0721412-1420. Andreasson G, Lindenberger U, Renstrom P, Peterson L. (1986) Torque developed at simulated sliding between sport shoes and an artificial turf. Am J Sports Med. 14(3):225- 230. Arnold JA, Coker TP, Heaton LM, Park JP, Harris WP. (1979) Natural history of anterior cruciate tears. Am J Sports Med. 7(6):305-313. Bellchamber TL, van den Bogert AJ. (2000) Contributions of proximal and distal moments to axial tibial rotation during walking and running. J Biomech. 33(1 1):1397- 1403. Bonstingl RW, Morehouse CA, Niebel BW. (1975) Torques developed by different types of shoes on various playing surfaces. Med Sci Sports. 7(2):127-131. Cawley PW, Heidt RS Jr., Scranton PE Jr., Losse GM, Howard ME. (2003) Physiologic axial load, frictional resistance, and the football shoe-surface interface. Foot Ankle Int. 24(7):551-556. Fauno P, Wulff Jakobsen B. (2004) Mechanism of anterior cruciate ligament injuries in soccer. Int J Sports Med. 27:75-79. Fernandez WG, Yard EE, Comstock RD. (2007) Epidemiology of lower extremity injuries among US. high school athletes. Acad Emerg Med. 14(7):641-645. General Sports Venue, LLC [Internet]. Rochester (MI): Product overview. Available at: http://wwwastroturfirsacom/producU. Accessed December 6, 2007 . Guise ER. (1976) Rotational ligamentous injuries to the ankle in football. Am J Sports Med. 4(1):1-6. Hammer D. (1981) Artificial playing surfaces. Athletic Training. 16: 127-129. Hirsch C, Lewis J. (1965) Experimental ankle joint fractures. Acta Orthop Scand. 36:408- 417. Lambson RB, Barnhill BS, Higgins RW. (1996) Football cleat design and its effect on anterior cruciate ligament injuries. A three year prospective study. Am J Sports Med. 24(2):]55-159. 53 McClay I, Manal K. (1988) A comparison of three-dimensional lower extremity kinematics during running between excessive pronators and normals. Clin Biomech. 13(3):]95-203. Nigg BM, Yeadon MR. (1987) Biomechanical aspects of playing surfaces. J Sports Sci. 5(2):117-145. PermaLife Products, LLC [Internet]. Guttenberg (NJ): PermaLife SportsFill. Available at: http://www.permalife.com/SportsFillProducts.asp. Accessed December 6, 2007. Powell JW, Schootman M. (1992) A multivariate risk analysis of selected playing surfaces in the National Football League: 1980-1989. An epidemiological study of knee injuries. Am J Sports Med. 20(6):686-694. Powell JW, Schootman M. (1993) A multivariate risk analysis of natural grass and AstroTurf playing surfaces in the National Football League 1980-1989. Int Turfgrass Soc Res J. 23:201-211. Robbins D. (1985) Anthropometry of motor vehicle occupants. Volume 3. Transportation Research Institute. DOT/HS 806 717. Shoemaker SC, Markolf KL, Dorey FJ, Zager S, Namba R. (1988, March) Tibial torque generation in a flexed weight-bearing stance. Clin Orthop Relat Res. 228:164-170. Shorten MR, Hudson B, Himmelsbach JA. (2003, July 6-12) Shoe-surface traction of conventional and in-filled synthetic turf football surfaces. In: Milbum, P. (ed.) Proc XIX International Congress of Biomechanics, University of Otago, Dunedin, New Zealand. Dunedin, NZ. International Society of Biomechanics. CD ROM abstracts and proceedings. Stacoff A, Nigg BM, Reinschmidt C, van den Bogert AJ, Lundberg A. (2000) Tibiocalcaneal kinematics of barefoot versus shod running. J Biomech. 33(11):1387- 1 395. Stanitski CL, McMaster JH, Ferguson RJ. (1974) Synthetic turf and grass: A comparative study. J Sports Med. 2(1):22-26. TerraSportsTech [Internet]. (The Netherlands): Terra-XPS brochure. Available at: http://www.terrasportstech.com/upload/File/terraxps_english.pdf. Accessed December 6, 2007 . Torg J S, Quedenfeld TC, Landau S. (1974) The shoe-surface interface and its relationship to football knee injuries. J Sports Med. 2(5):261-269. Torg J S, Stillwell G, Rogers K. (1996) The effect of ambient temperature on the shoe- surface interface release coefficient. Am J Sports Med. 24:79-82. 54 Villwock MR, Meyer EG, Powell JP, Fouty AJ, Haut RC. (2009) Football playing surface and shoe design affect rotational traction. Am J Sports Med. 37(3):518-525. 55 Chapter 4: External Rotation Ankle Injuries - Investigating Ligamentous Ruptures ABSTRACT: A majority of experiments that investigate external rotation injuries of the ankle joint produce fiacture rather than the soft tissue injuries reported in many clinical studies. In addition, two different methods of foot fixation have been used to study the biomechanical response and tolerance of the human ankle to external rotation of the foot/ankle complex. It was hypothesized that experiments with a younger specimen population will result in a high frequency of ligamentous injuries, prior to bone fiacture during excessive levels of external rotation of the foot/ankle complex. The torque, . rotation, and mode of soft tissue injury may also be a function of the type of fixation used to constrain the foot. Seven ankle pairs were tested by externally rotating the foot/ankle complex until diagnosed injury. Two different methods of foot fixation were studied: potted and taped constraint. Motion analysis of the fibula, tibia and talus was performed in four ankle pairs. The mean failure torque was 72 Nm. Differences in the failure mode were noted between the potted and taped groups. The posterior talofibular ligament was involved in the injury when the foot was constrained in potting material. The deltoid ligament failed when the foot was constrained using the taped and potted methods, but the fiequency of deltoid injury was higher for the taped foot. The higher rate of deltoid injury for the taped foot may be attributable to the additional talar motion during external rotation of the foot/ankle complex. The ankles tested with a potted foot failed at lower levels of foot rotation. This may imply that shoes with tight, stiff uppers may influence foot mechanics and therefore the potential for and location of soft tissue injury. 56 INTRODUCTION: Ankle sprains are one of the most common sports injuries (Lassiter et al., 1989; McConkey, 1987), accounting for ten percent to forty-five percent of sport-related injuries (Fallat et al., 1998; MacAuley, 1999). The severity of injury varies greatly and the player’s recovery time is related to the structures involved and their degree of damage. In the NFL (National Football League), excessive external rotation of the foot/ankle complex is often associated with significant time loss injuries (Boytim et al., 1991; Guise, 1976). These injuries typically involve the ligamentous structures of the ankle joint. The importance of individual ligamentous contributions to resistive torque during external rotation of the foot/ ankle complex has been investigated in numerous sectioning studies (Johnson & Markolf, 1983; Rasmussen et al., 1982; Xenos et al., 1995). This involves surgically cutting a ligament and quantifying its contribution to restraint of a particular joint motion, as sequential levels of disruption are introduced in the joint. Buckle transducers and strain gauges have also been used to show that there are relatively high forces developed in the ankle ligaments during external rotation of the foot (Bahr et al., 1998; Shybut et al., 1983). Yet, in contrast to the soft tissue injuries that are reported in many clinical studies on the ankle (Boytim et al., 1991; Edwards & DeLee, 1984; Hopkinson et al., 1990), experimental studies have typically generated a high frequency of bone fractures when the foot is externally rotated (Lauge-Hansen, 1950; Markolf et al., 1989; Schaffer & Manoli, 1987) In the current literature there are conflicting reports as to the location of the primary ligamentous restraint to external rotation of the foot/ankle complex. Nmnerous studies on the mechanisms of ankle injury deal with injuries to the syndesmosis and 57 anterior ligamentous structures (Hirsch & Lewis, 1965; Markolf et al., 1989; Stiehl et al., 1992), but a previous study using sectioning techniques also describes the important role of the posterior talofibular ligament (PTaF L) in the ankle’s resistance to external rotation of the foot/ankle complex (Stormont et al., 1985). In addition, Colville et al. (1990) measure strain in various ankle ligaments and conclude that the greatest strain experienced during dorsiflexion-extemal rotation is in the PTaF L. Clinicians also indicate a high frequency of cases involving injury to this posterior ligamentous structure (Colville et al., 1990; Fallat et al., 1998). Yet, some report that the PTaFL is rarely injured except in association with complete dislocation of the talus (Molus & Martin, 2008) There is limited documentation of laboratory studies that externally rotate the foot and induce isolated ligamentous injury of the ankle. Markolf et a1. (1989), for example, applied supination-extemal rotation to the foot and documents five cases of lateral ligamentous injury without bone fracture. Yet, no further description of the specific ligaments damaged is included in the manuscript. Rasmussen ( 1985) applied dorsiflexion-external rotation to the foot resulting in posterior talofibular ligament (PTaF L) rupture. Yet, failure levels of torque and rotation are not provided in the study. Other experimental studies produce ligamentous injury, but always in combination with bone fractures (Hirsch and Lewis, 1965; Lauge-Hansen, 1950; Stiehl et al., 1992). In a majority of manuscripts that describe external rotation injuries of the ankle joint, the age and gender of the cadaveric test specimens has not been reported (Hirsch and Lewis, 1965; Markolfeta1., 1989; Schaffer and Manoli, 1987). These variables may substantially affect both the failure load and the mode of failure in the joint, since most 58 ankle sprains occur in persons under the age of 35 years (Nilsson, 1983). Stiehl et al. (1992) investigated external rotation injuries of the ankle using male specimens with an age of 67 i 19 years. The experiment generated fibular fractures in combination with ligamentous injuries. The advanced age of these test specimens may explain the high fiequency of bone fi'actures that were produced in the study. Within the current literature, two different methods of foot fixation have also been used to study the biomechanical response and tolerance of the human ankle to external rotation of the foot. Stormont et al. (1985) rigidly fix the foot in a potting alloy and perform a sectioning experiment. The study concludes that the primary ligamentous restraints to external rotation of the foot are the calcaneofibular (CaF L) and posterior talofibular (PT aF L) ligaments. In contrast, Stiehl et al. (1992) constrain the foot with fiberglass cast tape and externally rotate the foot 90 degrees. The study produces injury to the anterior ligamentous structures, including the deltoid 1i garnent, anterior tibiofibular ligament (ATiF L), and interosseous ligament in association with fracture of the fibula and tibia. These contrasting data on the locations of the primary soft tissue restraints during external rotation of the foot may be attributable to differences in the method of foot fixation. Foot constraint may influence subtalar motion and the movement of the bony structures within the foot, thereby influencing the mode of injury during external rotation of the foot. It was hypothesized that experiments with a younger specimen population will result in a high frequency of ligamentous injuries, prior to bone fracture during excessive levels of external rotation of the foot. Measurement of the rotational moments, angular rotations, and modes of soft tissue injury may also be a function of the type of 59 experimental fixation used to constrain the foot. These experimental data may provide new information for the clinical diagnosis of injury to the ankle following excessive external rotations. The biomechanical data may also be used to help develop a biofidelic ankle surrogate that can be used in the evaluation of athletic shoe-surface interfaces for studies of injury risk (Villwock et al., 2009). MATERIALS AND METHODS: Torsion experiments were conducted on lower limbs from seven male cadavers (aged 40 j: 11 years). The limbs were procured through university sources, stored at -20 degrees Celsius and thawed to room temperature for 24 hours prior to testing. The tibia and fibula were sectioned approximately 15 cm distal to the center of the knee. The proximal end of the tibia and fibula shafts were cleaned with 70% alcohol and potted in a rectangular aluminmn tray with room temperature curing epoxy (Fibre Strand, Martin Senior Corp., Cleveland, OH). Two different manners of foot fixation were used in this series of experiments. Ten lower extremities were tested with the foot potted in a rectangular aluminum tray with room temperature curing epoxy (Fibre Strand) (Figure 4.1). Screws were placed into the calcaneous and the entire foot was surrounded and supported with the potting material, but care was taken to leave space around the medial and lateral malleoli. Four additional lower extremities were tested by constraining the foot with athletic tape (Elastikon, Johnson & Johnson, New Brunswick, NJ) onto a 22-cm x 10-cm polycarbonate plate which was then inserted into a rigid fixture (Figure 4.2). A tapered elastomeric insert (Shore Hardness 10A) with a maximum thickness of 2.5 cm was placed beneath the arch of the foot to simulate support that may be provided by a 60 shoe. Both methods of foot fixation were positioned in different degrees of flexion by means of interchangeable wedges placed underneath the foot plate. The foot was everted (10 to 15 degrees about an anteroposterior axis) in all tests (Figure 4.3). Figure 4.1: Close-up of cadaveric lower extremity mounted in testing device with foot constrained in potting material. Reflective marker arrays were used to conduct motion analysis using a Vicon system. 61 Figure 4.2: Cadaveric lower extremity with foot constrained to polycarbonate plate with athletic tape. The polycarbonate plate is inserted into a rigid fixture for testing. Reflective marker arrays were used to conduct motion analysis using a Vicon system. Vertical Linear Actuator Plate allowing X-Y adjustment Flexion Wedge Rotary Actuator Figure 4.3: Experimental setup performed on biaxial materials testing machine. 62 [0 CK de Sp) )1)" S11! fail m 0x: A custom, hydraulic, biaxial testing machine was built by mounting a 244 Nm rotary actuator Model SS-001-1V, Micromatic, Beme IN) onto a linear actuator frame (Model 312.21, MTS Corp., Eden Prairie, MN) with a vertically oriented linear actuator (Model 204.52, MTS Corp.). The actuators had separate controllers (Model 458.2 Microconsole for the linear actuator and Model 442 Controller for the rotary actuator, MTS Corp.). The rotational displacement was programmed by a waveform generator (Model 458.91 Microprofiler, MTS Corp.) that produced a haversine waveform. The foot was attached to the rotary actuator through a biaxial (torsion-axial) load cell (Model 1216CEW-2K, Interface, Scottsdale, AZ). The axis of rotation of the foot was aligned with the ankle center between the medial and lateral malleoli. The proximal end of the extremity was secured to the rotation locked linear actuator with a custom fixture designed to allow sufficient positioning for dorsiflexion and eversion of the foot. Each specimen was mounted with the tibia axis aligned with the linear actuator. Compressive preloads of two to three times body weight were applied through the tibia prior to the application of an external torque. A dynamic angular rotation was input with a position controlled waveform. Two different rates of rotation were used in this study, 0.5 Hz and 2 Hz. The rotation was increased by increments of five degrees in successive tests until diagnosed ligamentous injury or bone fracture. The mode of injury, failure load and failure angle of foot rotation were documented for each specimen. The last eight ankles (four pairs) were subjected to pre-test computed topography (CT) scans and a subsequent motion analysis of the fibula, tibia and talus during the external rotation tests using a Vicon motion capture system (Oxford Metrics Ltd., Oxford, United Kingdom). The CT scans were performed with reflective marker arrays 63 fixed to the fibula and tibia (Figures 4.1 and 4.2). The fibula array was attached to the lateral malleolus and the tibia array was positioned several centimeters proximal to the inferior articular surface. This allowed determination of transverse plane positions of the fibula and tibia markers with respect to their geometric centers using an open source DICOM viewer and analysis tool (OsiriX, Version 2.7.5, Open Source General Public License). Virtual points were identified in Vicon Bodybuilder (Oxford Metrics Ltd.) at these designated bone centers and tracked during each test to measure the translation of the distal segments of the fibula and tibia. The anterior-posterior translation, medial- lateral translation and internal/extemal rotation of the fibula and tibia were documented at peak foot rotation. This allowed the motion of the fibula relative to the tibia to be calculated, providing a measure of the motion at the syndesmosis. The rotations of the talus were measured by the inclusion of an additional array that was positioned on the superoposterior surface of the talus for the dorsiflexed specimens and on the superoanterior surface of the talus for the plantarflexed specimen. These analyses were performed on the test data from the experiment immediately preceding the test resulting in diagnosed gross failure of the ankle. Following the experimental testing, all soft tissue injuries and bone fractures were documented during a careful gross dissection of the joint. One way ANOVAs were performed with SigmaStat (Version 2.03, SPSS Inc., Chicago, IL) to compare failure torque and failure angle of foot rotation between the potted and taped ankles. Statistical significance was set at p < 0.05 for these analyses. 64 am tal0 4.4) the mid tibit RESULTS: The mean failure torque of the ankles with a potted foot was 69.8 i: 12.4 Nm with a mean failure angle of 41 .8 :l: 6.9 degrees (Table 4.1). Isolated avulsion of the posterior talofibular ligament (PTaF L) from the fibula was noted in four of the ten ankles (Figure 4.4). Distal fibular fractures were generated in three ankles, two of which passed through the anterior tibiofibular ligament (ATiF L) (Figure 4.5). Single incidents were noted of mid-substance PTaF L rupture, anterior deltoid ligament rupture (tibiotalar and tibionavicular), and a spiral fi'acture of the tibia and fibula. 65 8:- 8.2- 688 28 8.88 03.. 8888.8 88 E 87 N 88 8S :8 888888 3993 $889,893 38888 583. 88 88 88 8.8 88 88._ 88 888888 888.888 8888838 8.8 88 8: 8_ N 8: 8 S 88 .8888 8.88.888 88858 8.8 88 88 88 N 888888 8858 85 8.5888 23888 B888 88 N8 88 8.8 8: :88 :8 88888 6 H.838. 88:28 8588 88 _fie 88 _8 8 8.8 888 8.8.8 6 8588 88 8885 88 88 88 8.8 88 88._ 88 488888 H.812 8888.8 2388 88 Ema .. .. 88 N 88 8888 8888.888 8238 8E 88 88 88 8 83925 .8888 8888.888 8888858 an 88 88 88 8 8 888888 888883 .985 883 88.78 883 $3 988 83 85 888. _fifiam 3888. 8888. case 88538 83 E 82882.88 88328 5.88538 38 2 e33 882 8288:3085 2388 3:8 2.93 82.8235 . 83.8288 wagon E 3988.388 833 23.8... 88 3888 88.9880 3.53250 03:8 35 890,—. “:8 03.? Figure 4.4: Fibular avulsion of the posterior talofibular ligament Figure 4.5: Fibular fracture through the anterior tibiofibular ligament 67 The mean failure torque of the ankles with a taped foot was 78.5 i 18.1 Nm with a mean failure angle of 65.5 i 10.7 degrees (Table 4.2). Damage to the anterior portion of the deltoid ligament (tibiotalar and/or tibionavicular) was noted in three of the four ankles (Figure 4.6). Fibular fracture through the ATiF L was observed in one ankle. There was no significant difference in failure torque between the potted and taped foot groups, but a significant difference was noted in angle of foot/ankle complex rotation at failure (p <0.001) between the two groups. 68 :88- _.88- 583 8.88 8.8: 32.. 8838 888.3 86888883. 8: N8 8 N 888 8:; N8 8N88N8 8888.8 .1883 868% 888a... :: 88 8N 8.8 8N88N8 8.828833 858888888 N8 88 8N 8.8 88 8:8 :8 .8882 88.358833888888882. 88 88 8N 8.8 88 88._ a mNmmNm 888889 .8588 883 88.88 883 $3 988 A83 83 888. .888 3898. 8888. SEE 88388 83 E 889 888888 as, 838.98 .83 888 a 88882 82898 98882888 285 88 883.: ”N8 8.88: 69 (Tab MS MT; We] tapa With A Figure 4.6: Anterior deltoid rupture Prior to failure, the external rotation moment caused medial and posterior translation of the fibula relative to the tibia, when compared to non-weight bearing (Tables 4.3 and 4.4). The fibula translated medially an average of 3.02 mm when the foot was potted, and 4.31 mm when the foot was taped. The posterior translation of the fibula averaged 5.15 mm for both the potted and taped foot. The distal segment of the fibula externally rotated in relation to the tibia an average of five degrees in both the potted and taped foot experiments. The talus exhibited greater external rotation and plantarflexion with the taped foot in comparison to the potted foot (Tables 4.3 and 4.4). 70 88.888; 6.8888 5.8:NN8 8.38.8 €888.88 AN.N88.N- AN.888.N 88.8888 $888.8 3:88.88 88.888N8 888028. 8.8- _.8 N88 8.8 8.8_ 8.8- 8.N- 8.8- 8.8- 88 88 8888N8 8.8 8.88 8.88 8.: 8.8_ 8.8- 8.8 8.8 8.8 88 88 8N88N8 N.8 8._ 8.8N 8.N_ 8.8_ 8.N- 8.8 8.N 8.8 88 88 8888N8 8.8 N.8 8.8_ 8.8 8.8 N.8 8.8 8.8 8.8 88 88 8888N8 8288 8288 828-8 85:. 8388-8 8:88 8.8888 8:88 8.288 8888 88.28 888888 A883 A883 8888 8888888 zen-.888 8:5 8888.888..- EE 8888.888:- 2888. 885-8 22882: coca—m 82.588088 332 8883888858 9.8888 988888 88888888888 8883886 285 88.88888 2,8888 .3828 888 88888 2:888 8888828 8.28885 38 888 88882 82888 88882 ”8.8 8.888- 888888 88.32 2,888.88 88.388 A8.N88.88 8.38.8- A8.N88.8A8.888.8A8.:8.8 88.88 8.88 A888 8.88 688038 8.N 8.8 8.88 8.8 8.2 8.N 8.8 _ 8.8 88 88 8888N8 8.N 8.8 8.8N 8.8 N88 8.8- _.8 8.8- 8.N 88 88 8N88N8 8.8 8.8 8.8_ 8.8 8.8 8.8- 8.8 8._ 8.8 88 88 8888N8 8.8 8.N 8.: 8.8 8.8 N._- 8.N 8.8 N.8 88 88 8888N8 8288 8288 828.8 8588 8388-8 E:- 88588 8888 838 8888 88.28 888888 8888 A883 A883 88888 35888 8888 8888.888:- 888 88888888 2898 888-8 2288855 858on 808-58808“ E602 888688858 8 8.8888 98888 88888 88288 B8 388. 28 a 8 888.82 28888 €828 888 828888 85888 8.888888 8.83885 38 588 88882 888.88 88882 ”8.8 8.88.8 71 DISCUSSION: This study measured the rotational moments and angular rotations of the ankle that resulted in gross injury to ligaments and/or bone fracture during external rotation of the foot/ankle complex. The mean failure torque in this experiment, approximately 72 Nm, compared well with the current literature. Hirsch and Lewis (1965) document a mean failure torque of 75 Nm to produce fracture of the ankle joint during pronation- external rotation of the foot, and Stiehl et a1. (1992) record a mean failure torque for male specimens of 65 Nm to generate ankle fractures during external rotation of the foot. The modes of failure in the current study (posterior talofibular ligament (PTaF L) avulsions, deltoid ligament tears and fibular fiactures) were also comparable to the documented modes of failure in the current literature. The anterior tibiofibular ligament (AT iF L) was only involved in the injury in the event of a distal fibular fracture. Rasmussen (1985) forced dorsiflexion-external rotation injuries in two ankles. In both preparations, the PTaF L was involved in the injury. Stiehl et al. (1992) externally rotated the foot and documented fibula: fracture in combination with a torn ATiFL and deltoid ligament in eight of twelve specimens. Differences in the failure mode were noted between the potted and taped groups. The PTaF L was involved in the injury when the foot was constrained in potting material. The deltoid ligament failed when the foot was constrained using the taped and potted methods, but the frequency of deltoid injury was higher for the taped foot. These results support the hypothesis that the location of injury may be a function of the type of experimental fixation used to constrain the foot. The importance of the PTaF L when the foot was potted is in agreement with a sectioning study performed with similar 72 constraints that documents the contribution of the PTaF L in the ankle’s resistance to external rotation (Stormont et al., 1985). The frequency of deltoid injury with the taped foot is also comparable to the rate observed by Stiehl et al. (1992) in which the authors constrain the foot with fiberglass tape and externally rotate the foot. In the real world, this may imply that shoes with tight, stiff uppers, as described by Villwock et al. (2009), may influence foot mechanics and therefore the potential for changes in the location of soft tissue injury. Similar effects on ankle injury based on boot stiffness have been previously documented in snowboarding (Delorme et al., 2005). The motion analysis contributes to an understading of the mechanisms of injury. The higher rate of deltoid injury for the taped foot may be attributable to the additional talar motion during external rotation of the foot/ankle complex. The increased plantarflexion of the talus in the taped foot may have released tension in the PTaF L and increased tension in the anterior deltoid, thereby allowing additional external rotation and further increasing strain in the anterior deltoid ligament. The limited talar motion when the foot was potted may be due to subtalar constraint imposed by the potting material. Conversely, the increased talar motion when the foot was taped may be due to the ability of the arch to collapse. It is interesting to note that the potted specimen with the deltoid injury was the youngest specimen (19 years of age), and exhibited greater external talus rotation along with greater external fibula rotation than the other potted specimens. The increase in fibular rotation may be attributed to the better bone quality of this specimen. The fibula may have been less brittle and able to respond to the increase in PTaF L tension, thereby avoiding the avulsion type injury noted in several ankles. The strain in the anterior 73 deltoid ligament may also have been increased by the additional plantarflexion of the talus noted in this specimen compared to the other potted specimens. The potted and taped foot groups failed at comparable levels of torque, but significantly different levels of foot/ankle complex rotation were recorded in the study. The ankles with a potted foot failed at smaller input rotations. Research by Lundberg et al. (1989a; 1989b) suggests that rotations of the bones within the foot during eversion and external rotation may act as torsion dissipating devices. This implies that a rotation dependent injury mechanism may be influenced by constraint of the foot (Figure 4.7). For example, a shoe that allows subtalar motion and natural movement of the bone structures within the foot may require greater foot rotation to generate an injury. Figure 4.7: Rotation dependent injury mechanism may involve the player lying prone as another player lands on his ankle, forcing the foot to externally rotate. In a study by Taylor et al. (1992) that examined 44 football players with syndesmotic sprains, a positive diagnosis was based on tenderness around the 74 syndesmosis. The pain associated with a syndesmotic sprain may be the result of excessive strain in the ATiF L resulting in microdamage, rather than a visible rupture. Colville et a1. (1990) measure strain in the lateral ankle ligaments during dorsiflexion and external rotation of the foot and document strains in the PTaF L approximately twice those in the ATiF L, while strain in the posterior tibiofibular ligament (PTiFL) is negligible. This may explain the number of PTaFL injuries in the current study, with no cases of isolated syndesmotic injury. The results of this analysis indicated that the ankles exhibit posterior (5.1 mm) and medial (3.0 to 4.3 mm) translations of the fibula relative to the tibia, with external rotation (5.1 to 5.5 degrees) of the fibula relative to the tibia. These motions exceeded those recorded in the literature for a healthy population subjected to a 7.5 Nm external rotation moment (Beumer et al., 2003). Healthy volunteers in that study experienced an average fibular displacement in relation to the tibia of 1.48 mm in the medial direction, 1.87 mm in the posterior direction, and an external rotation of 3.85 degrees. Although the fibula translations recorded in the current study were greater than those for healthy volunteers, the clinical implications of these cadaver data and their potential for generating microdamage in the syndesmosis and associated tenderness indicative of a high ankle sprain are yet unknown. A limitation of this study was the frequency of bone avulsion. injuries at the insertion of the posterior talofibular ligament. While a younger aged specimen population was used to try and limit bone fracture, avulsions still occurred. If the avulsion injuries were avoided, the anterior deltoid may have been the vulnerable soft tissue, or “weakest link”, for the specimens tested with a potted foot. Other studies have shown, in fact, that the PTaF L is stronger than portions of the anterior deltoid ligament 75 (Butler & Walsh, 2004; Siegler et al., 1988). If the bone quality would have been more representative of the typical, younger athlete, the anterior deltoid may have been the location of primary failure, as seen in specimen 32532L. The number of avulsions may also be attributed to the speed of testing which was limited to control inertial effects in the current experimental setup. Past research on the knee suggest that the mode of ligamentous injury may be dependent on the strain rate. Avulsions may occur more often at low rates, while midsubstance failures are fiequently documented at high rates (Crowninshield & Pope, 1976). Another limitation of the current study was that the foot restraint, in terms of the potential shoe design issue, was not more completely studied at this time. In conclusion, following excessive external rotation of the foot/ankle complex this study documented isolated ligament ruptures in the PTaF L and anterior portions of the deltoid ligament. Damage to the ATiFL only occurred in combination with fibular fiacture. Fibular motions during external rotation of the foot exceeded those measured in viva for a healthy population, but the potential clinical implications of these data and their potential for generating tenderness in the syndesmosis, indicative of a “high ankle” sprain, are currently unknown. Finally, the amount of constraint offered by a shoe and its upper may influence the potential for and determine the location of soft tissue injuries in the anterior or the posterior aspects of the ankle following excessive levels of external rotation of the foot/ankle complex on an athletic field. 76 REFERENCES Bahr R, Pena F, Shine J, Lew WD, Engebretsen L. (1998) Ligament force and joint motion in the intact ankle: a cadaveric study. Knee Surg Sports Traumatol Arthrosc. 62115-121. Beumer A, Valstar ER, Garling EH, Niesing R, Ranstarn J, Lofvenberg R, Swierstra BA. (2003) Kinematics of the distal tibiofibular syndesmosis. Acta Orthop Scand. 74(3):337- 343. Boytirn M], Fischer DA, Neumann L. (1991) Syndesmotic ankle sprains. Am J Sports Med. 19(3):294-298. Brosky T, Nyland J, Nitz A, Caborn DN. (1995) The ankle ligaments: consideration of syndesmotic injury and implications for rehabilitation. J Orthop Sports Phys Ther. 21:197-205. Butler AM, Walsh WR. 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(1988) The mechanical characteristics of the collateral ligaments of the human ankle joint. Foot and Ankle. 82234-242. Shybut GT, Hayes W, White AA. (1983) Normal pattern of ligament loading among the ' lateral collateral ankle ligaments. Trans OrthOp Res Soc. 8:15. Stiehl JB, Skrade DA, Johnson RP. (Dec, 1992) Experimentally produced ankle fractures in autopsy specimens. Clin Orthop Relat Res. 285:244-249. Stormont DM, Morrey BF, An KN, Cass JR. (1985) Stability of the loaded ankle. Relation between articular restrain and primary and secondary static restraints. Am J Sports Med. l3(5):295-300. Taylor DC, Bassett PH. (1993) Syndesmosis ankle sprains: diagnosing the injury and aiding recovery. Physician Sportsmed. 21(12):39-46. Taylor DC, Englehardt DL, Bassett PH. (1992) Syndesmosis sprains of the ankle. The influence of heterotopic ossification. Am J Sports Med. 20(2): 146-1 50. Turco VJ. (1977) Injuries to the ankle and foot in athletics. Orthop Clinics North Am. 8:669-682. Villwock MR, Meyer EG, Powell JP, Fouty AJ, Haut RC. (2009) Football playing surface and shoe design affect rotational traction. Am J Sports Med. [Epub ahead of print] PMID: 19168808. Williams GN, Jones MH, Amendola A. (2007) Syndesmotic ankle sprains in athletes. Am J Sports Med. 35(7):l 197-1207. Xenos J S, Hopkinson WJ, Mulligan ME, Olson EJ, Popovic NA. (1995) The tibiofibular syndesmosis: evaluation of the ligamentous structures, methods of fixation, and radiographic assessment. J Bone Joint Surg Am. 77:847-856. 79 Chapter 5: Development and Evaluation of a Surrogate Ankle for Use with a Rotational Traction Measurement Apparatus. ABSTRACT: Biofidelic devices are used in the automobile industry to assess injury risk during a vehicular accident. Similar biofidelic devices may have broad applicability in the field of sports injury prevention and could be used to enhance player safety. Ankle sprains constitute one of the most common sports injuries. Past studies have suggested that high rotational traction at the shoe-surface interface may increase the likelihood of lower extremity injury. Researchers have assessed this risk by measuring the peak torque during an applied rotation. On the other hand, ankle sprains may be dependent upon the amount of strain developed in the ankle ligaments during rotation of the foot/ankle complex, not the magnitude of torque. The current study quantifies the torsional stiffness of the human foot/ankle complex based on cadaver experiments. The development of a surrogate foot/ankle complex is then detailed and compared to the human response. Lastly, the results of a rotational traction study on a couple football shoe-surface interfaces are presented using the surrogate ankle. The testing resulted in a new outcome variable, peak twist of the ankle, that may allow assessment of the risk of injury to the ankle due to excessive rotational traction at the shoe-surface interface. 80 INTRODUCTION: Information gathered from healthy volunteer studies and cadaver research has been used to create anthropometric test devices for the automobile industry in order to predict injury risk during a vehicular accident (Forman et al., 2006; McDonald et al., 2003; Tomvall et al., 2007). These test devices, or “crash test dummies”, are usually instrumented to record data about the dynamic behavior of the dummy during a crash. Similar biofidelic devices may have broad applicability in the field of sports injury prevention and could be used to enhance player safety. In the National Football League (NFL), ankle sprains account for about 10% of all sports-related reported injuries (Powell and Schootman, 1993). It is generally accepted that excessive rotational traction may precipitate some of these lower extremity injuries (Bonstingl et al., 1975; Lambson et al., 1996; Nigg and Yeadon, 1987; Torg et al., 1974). Previous studies that analyze injury risk due to traction at the shoe-surface interface have measured the peak torque during an applied rotation of the shoe (Cawley et al., 2003; Lambson et al., 1996; Livesay et al., 2006; Torg et al., 1974). Yet, tissue strain may be a better indicator of injury tolerance than load due to the viscoelastic nature of the sofi tissues involved in ankle injuries (Boytim et al., 1991; Edwards and DeLee, 1984). For example, previous studies have shown that the ultimate tensile strength (UTS) of soft tissues, including ligaments and tendons, increases as strain rate increases, while the ultimate strain is not affected (France et al., 1987; Ng et al., 2004). The ligamentous damage experienced in an ankle sprain may be brought about by mechanical disruption due to excessive elongation and deformation of one or more ligaments. Therefore, 81 measurement of ankle twist during an applied axial rotation at the shoe-surface interface may provide a better indicator of ankle injury risk than torque alone. The development of a biofidelic ankle may be used as a tool to assess ankle injury risk due to the shoe-surface interface. The goal of this study was to quantify the torsional stiffness of the human foot/ankle complex, then design a surrogate foot/ankle complex to mimic the human response. The surrogate would then be incorporated into an existing rotational traction apparatus used to assess peak torque at the shoe-surface interface (V illwock et al., 2009a; 2009b). Measurement of the ankle twist during an applied external rotation moment applied to the shoe may provide an additional tool that can help assess the risk of ankle injury due to the shoe-surface interface characteristics. MATERIALS AND METHODS: The data from a previous cadaver experiment was re-analyzed to determine the torsional stiffness of the human ankle joint (V illwock et al., 2009c). The previous tests involved externally rotating ten ankle joints until failure. Briefly, the foot was potted in room temperature curing epoxy (Fibre Strand, Martin Senior Corp., Cleveland, OH). Screws were placed into the calcaneous and the entire foot was surrounded and supported with the potting material. Prior to each test, the foot was everted and the ankle was placed into various degrees of flexion. Compressive preloads of 2-3 times body weight were applied. The specimens were loaded by incrementally increasing the angle of rotation by five degrees until a grossly diagnosable injury. Graphs werethen constructed of torque versus ankle rotation for each successive experiment. The torque-rotation data was taken from each subfailure experiment. The failure experiment was not included for 82 the determination of torsional stiffness. The primary stiffness was determined by a linear regression through the experimental data up to 20 degrees of foot/ankle complex rotation. The secondary stiffness was determined by a linear regression through the data above 35 degrees of foot/ankle complex rotation. The overall stiffness was calculated from a linear regression through the entire data set. The surrogate lower leg fi'om the rotational traction testing apparatus (Figure 5.1) was then re-designed to match the torsional stiffness from the cadaver experiments. The leg consisted of a hollow aluminum tibia connected to a rigid foot made from room temperature curing epoxy (Fibre Strand, Martin Senior Corp., Cleveland, OH). The foot was connected to the tibia and allowed to rotate about the tibia axis through a small channel (Figure 5.2). The length of the channel and the material used to fill the channel could be modified, allowing control of torsional stiffness at the ankle. The elastomeric materials were neoprene (Part # 8981K16, McMaster-Carr, Ehnhurst, 11) in various degrees of hardness. These bumpers were 0.25 inches thick, 0.75 inches tall and filled the entire length of the channel (2.5 inches). 83 _ Input Rotary Encoder 8 ._ , , Surrogate Lower Leg 53' Dynamic Normal Force Compressive Weights ..1: lntemal (Normal Force) _..-.... Leg Rotation “55 Torsion Drop Weights Torsion Pulley —£ _ if Deformable ' Elastomer Biaxial Load Cell —._;.,‘._, for Compliant Ankle Rotary Ankle Encoder Football Shoe .--. Mounted on a Operator .4. ‘ Rigid Foot Model Standing _ :.. 1.: 1 , Platform Remov le Resultant External Torque at Wheels the Shoe-Surface Interface Figure 5.1: Rotational traction testing apparatus (V illwock et al., 2009a; 2009b) Figure 5.2: Posterior view of the surrogate lower extremity. An angular displacement transducer inside of the tibia shaft recorded foot/ankle complex rotation. The channel was filled with neoprene rubber to simulate the torsional stiffness of the ankle. 84 The surrogate lower leg was evaluated using the same testing protocol as previously described in the cadaver ankle study (V illwock et al., 2009c). Briefly; a custom biaxial testing machine was used to apply a compressive load and a rotary moment (Figure 5.3). The foot last was attached to the rotary actuator through a biaxial (torsion-axial) load cell (Model 1216CEW-2K, Interface, Scottsdale, AZ). The axis of rotation was aligned with the center of the surrogate tibia. The proximal end of the surrogate tibia was secured to the rotation locked linear actuator with a custom fixture designed to allow sufficient positioning for alignment. Each specimen was mounted with the surrogate tibia axis aligned with the linear actuator. Compressive preloads of 100N were applied through the surrogate tibial shaft prior to the application of an external torque. A dynamic angular rotation was input with a rotation controlled waveform at 1 Hz. The rotation was increased in increments of five degrees in successive tests until the torque exceeded 110 Nm. At the conclusion of each experiment, the ankle was manually rotated until contact with the end of the channel to ensure a consistent starting position. The torsional stiffness was determined in a manner similar to that previously described for the cadaver specimens. 85 Biaxial Load Cell Rotary . Actuator -:> 1' - ‘1’ Figure 5.3: Surrogate lower extremity mounted on the material testing machine. The traction measurement apparatus (Figure 5.1) was then utilized to evaluate the biofidelic ankle on an indoor playing surface (AstroPlay, Southwest Recreational Industries, Leander, Texas). The surface was installed in an indoor sports complex six years prior to the tests. Four shoes were evaluated on the surface. These shoes were fi'om the upper and lower ranges of peak torque and rotational stiffiress in a previously documented study on this surface (Villwock et al., 2009a): Nike Blade 11 TD, Adidas Turf Hog LE, Adidas Corner Blitz 7 MD and Nike Air Zoom Superbad FT. The testing procedure followed the format previously described (Villwock et al., 2009a). Briefly, a 1000 N compressive load was applied followed by a 90 degree internal rotation of the surrogate leg, resulting in an extemally directed ground reaction torque on the foot. The entire cleat pattern was in contact with the ground, and the center of rotation was at the 86 midfoot. Rotations of the leg and ankle were recorded using angular displacement transducers (Model 0605-S7104010201, Trans-Tek Inc., Ellington, CT). Five trials were performed for each shoe-surface combination. The test apparatus was repositioned between trials to a new, adjacent section of turf. Peak torque and rotational stiffiress, as previously defined (V illwock et al., 2009a), were documented and used in the statistical analyses. In addition, the peak rotation of the ankle during each trial was recorded and analyzed. A one way ANOVA was performed with SigmaStat (Version 2.03, SPSS Inc., Chicago, IL) to assess differences between shoe models, with repeated measures across trials (n=5). Tukey post- hoc tests were used to evaluate differences in the mean values between shoes when such effects were throught to be greater than would be expected by chance. Statistical significance was set at p < 0.05 for all analyses. RESULTS: Data from the previous cadaver study by Villwock et al. (2009c) was re-analyzed to determine the torsional stiffiress of the human ankle. A torque versus foot/ankle complex rotation plot was constructed (Figure 5.4). The primary stiffness was determined to be 1.24 d: 0.49 Nm/deg, increasing to a secondary stiffiress of 2.03 i 0.64 Nm/deg, with an overall stiffness response of 1.68 :1: 0.26 Nm/deg 87 120 100 ~ 80 - 60 - 40- { 20~ , Torque (Nm) o I l l J I T f 0 10 20 30 40 50 60 70 80 FootlAnkle Complex Rotation (degrees) Figure 5.4: Torque versus foot/ankle complex rotation from a cadaver study by Villwock et al. (2009c). This graph depicts the average results, with standard deviations, calculated from ten cadaver lower extremities in five degree incremental trials. Trendlines are included for the primary and secondary torsional stiffiresses. The data used to construct this graph does not include the failure-level experiments. 88 The surrogate ankle design was evaluated with several neoprene bumpers representing various levels of hardness. The torque versus foot/ankle complex rotation was plotted for each rubber (Fig 5.5). The primary stiffness ranged from 0.9 to 2.4 Nm/degree, the secondary stiffness ranged from 1.0 to 3.8 Nm/degree, and the overall stiffness ranged from 1.2 to 3.0 Nm/degree: The high and low stiffnesses were produced with the 60A and 30A durometer materials, respectively (Table 5.1). Table 5.1: Torsional stiffness values (Nm/deg). The primary stiffiress was determined in a linear regression through all data points up to 20 degrees of foot/ankle complex rotation. The secondary stiffness was then determined in a linear regression through all data points above 35 degrees of foot/ankle complex rotation. The overall stiffness was based on a linear regression through the entire data set. Neoprene Hardness Primary Secondary Overall 30A 0.92 l .04 1.20 40A 0.98 2.26 1.80 50A 1.63 2.74 2.40 60A 2.42 , 3.80 3.00 89 120 - 60A 50A 100 s ' ' 40A 80 - A ? 30A 5 o 60 - 8 A ° 0 .— 0 40 ~ : U 20 ‘t' - o I ‘F I I I I I 1 - O 10 20 3O 40 5O 60 7O 80 Foot/Ankle Rotation (degrees) Figure 5.5: Torque versus foot/ankle complex rotation data fiom the surrogate tests. The results are fi'om neoprene rubber bumpers of varying hardness, as measured on the durometer Shore A hardness scale. Trendlines are included for the primary and secondary torsional stiffness. For reasons to be discussed later, the traction measurement apparatus (Figure 5.1) was tested on an AstroPlay installation with neoprene 50A used as the elastomeric bumper in the ankle joint. The Adidas Turflrog produced the lowest peak torque, 80 Nm (Figure 5.6). The Adidas Blitz generated the highest rotational stiffiress, 5.1 Nm/degree, and the highest rotation of the ankle at 36.5 degrees (Figures 5.7 and 5.8). 90 110 T ..1 rll} E 5 §_ 90 h l :3 l g 80 8 1 70 .1 : ,_ = 4 r < r 60 f D Bladell Blitz Superbad TufiHog Figure 5.6: Box plot of peak torque (Nm) for each shoe. The line near the center of the box represents the median value, the box represents the inter-quartile range and the whiskers represent the range. Arrows represent significant differences (p <0.05). 91 a 5.5 w 2 I E 5 4.5 r m 8 c 3.5 "' SE ('5 :;:r '5 2.5 8 I 3‘3 ‘5 15 *——’. . It 2 ' , A ‘ f 0.5 = N '0 C) a: E to o “O m .9 I 5.3 q; E m 3' I— (I) Figure 5.7: Box plot of rotational stiffness (Nm/deg) for each shoe. The line near the center of the box represents the median value, the box represents the inter-quartile range and the whiskers represent the range. Arrows represent significant differences (p <0.05). 92 37 ,.8 1 'T' m e 2 U35 4: 9. E 34 3 |_ - 2 33 E E5! _ x 32 - E e > 1 31 ‘ > 4 F 30 4 D E E '8 8’ '0 m '9 ,E L.“ a) 3 m 3' l— a) Figure 5.8: Box plot of peak rotation of the ankle (degrees) for each shoe. The line near the center of the box represents the median value, the box represents the inter-quartile range and the whiskers represent the range. Arrows represent significant differences (p <0.05). 93 DISCUSSION: The torsional stiffiress values from the cadavers in the current study were comparable to those presented in the literature. Stiehl et al. (1992) externally rotate the foot/ankle complex until failure and measure the torsional stiffness during the first 20 degrees of rotation. The authors note an average value for male specimens of 1.21 Nm/degree, compared to the average value in the current study of 1.24 Nm/degree over the same range of rotation. Schaffer and Manoli (1987) externally rotate the foot/ankle complex until failure and measure the torsional stiffness, ignoring the initial response- The authors note an average value of 2.14 Nm/degree, which was comparable to the secondary stiffness of 2.03 Nm/degree in the current study. The surrogate ankle joint was constructed with neoprene rubber. This material was chosen for its resiliency and durability (McMaster.com, 2008). The variations in hardness affected the torsional stiffness of the ankle. The material that provided a response most similar to the cadaver tests had a hardness of 40A. However, the in viva response of the ankle joint may be influenced by muscle activation. Mote and Lee (1982) measure the torsional stiffness at the ankle joint in a healthy volunteer. The response was limited to external rotations below 6 degrees, resulting in a stiffness of 1.27 Nm/degree when the subject was 100 percent weight bearing. This measurement is comparable to the results of the cadaver tests in the current study. The authors note that the percentage of weight bearing and the amount of muscle tension could vary the torsional stiffiress of the ankle. For example, the torsional stiffiress of the ankle increases from a state of minimal to maximal muscle activity by approximately twenty-eight percent (Mote and Lee, 1982). 94 The neoprene that most closely resembled the in vivo response of the ankle may then be the SOA durometer material. This material provided slightly greater torsional stiffness than the cadaver ankle, amounting to an increase in stiffness of thirty-one percent for the primary range and thirty-five percent over the secondary range. This is similar to the twenty-eight percent increase noted due to muscle activation in the in vivo study by Mote and Lee (1982). No specifications had been defined for the internal/external rotational degree of fieedom for the Thor-Lx crash test dummy (Shams et al., 1999), but Neoprene 50A was chosen as the elastomer bumper in the biofidelic ankle for the THOR-FLx crash test dummy (Shams et al., 2002). The surrogate ankle was evaluated with the rotational traction testing apparatus on an AstroPlay surface using Neoprene 50A as the deformable elastomer in the ankle joint. The results of these experiments were compared to a previous study with an identical testing protocol, but a more rigid ankle joint (V illwock et al., 2009a). The rotational stiffness values documented in this study for each shoe were within 1 Nm/degree of those presented previously by Villwock et al. (2009a). The magnitude of peak torque was similar for the Nike Blade II, Adidas Blitz and Adidas Tuerog in comparison to the previous study (V illwock et al., 2009a). The greatest discrepancy in peak torque between the two studies existed for the Nike Superbad shoe, which generated a peak torque that was twenty-five percent lower in the current study. It is believed that the higher torque in the previous study was due to the high torsional stiffness (approximately 11 Nm/degree) of the surrogate ankle joint (Villwock et al., 2009a). With a stiff ankle joint, a majority of the ninety degree input leg rotation occurred between the shoe and surface. In the current study, the ankle joint was more compliant and had a torsional stiffness of 2.4 95 Nm/degree with the neoprene 50A bumper. This resulted in more of the input leg rotation occurring at the ankle joint and less rotation between the shoe and surface. In the case of a shoe with a pliable upper (Nike Superbad), this provided less opportunity for the leading edge of the shoe to twist and plow into the surface causing an increase in torque (V illwock et al., 2009a). The discrepancy of torque between the two studies for the Nike Superbad shoe illustrates the influence that the magnitude of rotation has on the risk of ankle injury for certain shoe-surface interface combinations. Future development of the testing apparatus may include the incorporation of a torque controlled input, rather than a fixed level of leg rotation. This would allow the input to simulate the torque threshold documented in previous cadaver tests, and measure the amount of ankle and shoe rotation that occurs for a given shoe-surface interface. Twist of the ankle joint was a new variable introduced in this rotational traction study. The significantly higher rotation of the ankle with the Adidas Blitz shoe on the AstroPlay surface may be due to the shoe’s rigid upper material and its high rotational stiffness. The high rotational stiffness associated with the Adidas Blitz resulted in the ankle joint experiencing larger magnitudes of torque early in the rotation and may have generated the additional twist of the ankle joint. It is interesting to note that the peak torque for each of these shoe models exceeded the torque-tolerance, based on cadaver data at 72 Nm (V illwock et al., 2009c). However, the peak twist in the ankle for each of the shoe models did not exceed the tolerance data of 42 degrees based on these previous cadaver tests (Villwock et al., 20090). This might imply that rotation of the ankle may be a more realistic variable to monitor for injury risk assessment, since not everyone gets ankle injuries in these shoes. 96 Further studies, in concert with injury studies from the field, will be needed to better determine if torque or rotation of the foot/ankle complex would be the best measure of injury potential in the ankle using the surrogate test device. Development of the surrogate lower extremity should also include the incorporation of a biofidelic knee joint. This would allow comparisons between ankle and knee twist to determine which joint may be more at risk of injury, given an applied rotation or torque via specific shoe-surface interface conditions. The response of the lower extremity to excessive internal rotation of the foot/ankle complex should also be studied as this mechanism is often associated with anterior cruciate ligament injury (Meyer et al., 2008). Development of additional degrees of freedom for the ankle might be another advancement that may generate more physiological responses of the lower leg at the shoe-surface interface. For example, medial and lateral ankle sprains could be due to shear forces applied to the lower extremity while the foot is planted on the surface (Boytim et al., 1991). If ultimate strain is a better indicator of soft tissue injury risk in the ankle (and knee) than ultimate stress, measuring the magnitude of peak torque at the shoe-surface interface may not be an adequate injury predictor. Measuring rotation in the ankle may provide a measure by which peak torque and rotational stiffness are both integral to the outcome variable: injury risk assessment. In this regard, a biofidelic ankle would be crucial for evaluation of the potential for injury to the ankle (or knee) due to mismatches in shoe-surface interface designs. 97 REFERENCES Bonstingl RW, Morehouse CA, Niebel BW. (1975) Torques developed by different types of shoes on various playing surfaces. Med Sci Sports. 7(2):127-13l. Boytim MJ, Fischer DA, Neumann L. (1991) Syndesmotic ankle sprains. Am J Sports Med. 19(3):294-298. Cawley PW, Heidt RS Jr., Scranton PE Jr., Losse GM, Howard ME. (2003) Physiologic axial load, fiictional resistance, and the football shoe-surface interface. Foot Ankle Int. 24(7):551-556. Edwards GS, DeLee JC. (1984) Ankle diastasis without fracture. Foot Ankle. 4(6):305- 312 Forman J, Lessley D, Shaw CG, Evans J, Kent R, Rouhana SW, Prasad P. (2006) Thoracic response of belted PMHS, the Hybrid III, and the THOR-NT mid-sized male surrogates in low speed, frontal crashes. Stapp Car Crash J. 50:191-215. France EP, Paulos LE, Abbott PJ, Roberts PF, Mulric LA, Lernaster JH, Kazarian LE. (1987) Failure characteristics of the medial collateral ligament of the knee: Effects of high strain rate. Aviat Space Environ Med. 58:488. Lambson RB, Barnhill BS, Higgins RW. (1996) Football cleat design and its effect on anterior cruciate ligament injuries. A three year prospective study. Am J Sports Med. 24(2):]55-159. Livesay GA, Reda DR, Nauman EA. (2006) Peak torque and rotational stiffness developed at the shoe-surface interface. Am J Sports Med. 34(3):415-422. McDonald JP, Shams T, Rangarajan N, Beach D, Huang T, Freemire J, Artis M, Wang Y, Haffner M. (2003) Design and development of a THOR based female crash test dummy. Stapp Car Crash J. 47:551-570. McMaster-Carr [Internet]. Commercial-strength neoprene rubber technical information. Supply catalog p. 3440. Available at: http://www.mcmaster.com/ Accessed Nov 7, 2008. Meyer EG, Baumer TG, Slade JM, Smith WE, Haut RC. (2008) Tibiofemoral contact pressures and osteochondral microtrauma during anterior cruciate ligament rupture due to excessive compressive loading and internal torque of the human knee. Am J Sports Med. 36(10):l966-1977. Mote CD Jr, Lee CW. (1982) Identification of human lower extremity dynamics in torsion. J Biomech. 15(3):211-222. 98 Ng BH, Chou SM, Lim BH, Chong A. (2004) Strain rate effect on the failure properties of tendons. Proc Inst Mech Eng [H]. 218(3):203-206. Nigg BM, Yeadon MR. (1987) Biomechanical aspects of playing surfaces. J Sports Sci. 5(2):]17-145. Powell JW, Schootman M. (1993) A multivariate risk analysis of natural grass and AstroTurf playing surfaces in the National Football League 1980-1989. Int Turfgrass Soc Res J. 23:201-211. Schaffer JJ, Manoli A. (1987) The antiglide plate for distal fibular fixation. J Bone Joint Surg Am. 69-A(4):596-604. Shams T, Beach D, White R, Rangarajan N, Haffrrer M, Eppinger R, Pritz H, Kuppa S, Beebe M. (1999) Development and design of THOR-Lx: The Thor lower extremity. Proc 43“1 Stapp Car Crash Conference. Society of Automotive Engineers. Warrendale, PA: 141-160. Shams T, Beach D, Huang T, Rangarajan N. (2002) Development of THOR-FLx: A biofidelic lower extremity for use with 5th percentile female crash test dummies. Stapp Car Crash J. 46:267-283. Stiehl JB, Skrade DA, Johnson RP. (Dec, 1992) Experimentally produced ankle fractures in autopsy specimens. Clin Orthop Relat Res. 285:244-249. Torg J S, Quedenfeld TC, Landau S. (1974) The shoe-surface interface and its relationship to football knee injuries. J Sports Med. 2(5):261-269. Tomvall FV, Holmqvist K, Davidsson J, Svensson MY, Haland Y, Ohm H. (2007) A new THOR shoulder design: a comparison with volunteers, the Hybrid III, and THOR NT. Traffic Inj Prev. 8(2):205-215. Villwock MR, Meyer EG, Powell JP, Fouty AJ, Haut RC. (2009a) Football playing surface and shoe design affect rotational traction. Am J Sports Med. 37(3):518-525. Villwock MR, Meyer EG, Powell JP, F outy AJ, Haut RC. (2009b) The effects of various infills, fiber structures, and shoe designs on generating rotational traction on an artificial surface. J Sports Eng Tech. 223(1):]1-19. Villwock MR, Meyer EG, Powell JP, Haut RC. (2009c) A biomechanical investigation of ankle injury under external foot/ankle complex rotation using the human cadaver model. J Appl Biomech. In Review. 99 Chapter 6: Conclusions and Recommendations for Future Research Conclusions: This thesis explores the football shoe—surface interface and its potential relationship to injury risk. It attempts to understand the mechanics of the third- generation, artificial surface. Other investigators have assessed peak torque on artificial surfaces, but no one has tried to identify the surface variables which contribute to rotational traction. By understanding the mechanics of the materials, guidelines may be proposed in an effort to consider injury prevention during the design phase of artifical surfaces and shoes. This thesis also proposes a novel device that can be used to predict ankle injury risk based on ankle deformation rather than peak torque. Chapter 1 documented the need for further analyses into the risk of potential injury while playing football on a third-generation, artificial surface based on torque. Specifically, the need for rotational traction measurements of modern football shoes on infill based artificial surfaces using physiological loading conditions. Chapter 2 investigated the rotational traction of ten football shoes on the most commonly used surfaces in American football. It was hypothesized in this chapter that artificial surfaces would generate higher rotational tractions than natural grass surfaces. It was also hypothesized that rotational traction characteristics would be associated with the football shoe cleat pattern and materials used in the shoe’s upper. The results demonstrated that the AstroPlay and FieldTurf surfaces in this study yielded significantly higher peak torque and rotational stiffness in comparison to the natural grass surfaces. In addition, the natural grass surfaces were significantly different from each other, with the sand 100 based soil surface producing higher peak torque than the native Michigan soil surface. With the exception of the turf style shoe design, cleat pattern was not found to influence rotational traction measurements. The model of shoe, however, did significantly affect rotational stiffness. This may be due to differences in the structural integrity and material composition of the shoe’s upper. Chapter 3 further investigated the influence of infill material and fiber structure on generating rotational traction on third-generation, artificial surfaces. It hypothesized that rotational traction of the artificial surface would be largely influenced by the infill layer. It was found that the infill produced by cryogenic fiagmentation generated significantly higher torque than the ground or extruded rubber. It was believed that the compact structure of the infill layer due to the small size of the cryogenic particles increased the cleated shoe’s resistance to rotation. The presence of a nylon root zone in the fiber structure was also found to significantly reduce peak torque. This variable most likely affected torque generation by reducing the compactness of the infill layer. The effect of cleat pattern was statistically apparent in this analysis due to the similar structure of the tested surfaces. The cleat patterns identified by larger perimeter cleats (12 Studded and Edge) produced significantly higher torques than the other design groups. Chapter 4 documented ankle injuries that result fi'om excessive external rotation, possibly related to foot fixation in American football. It was hypothesized that experiments with a younger cadaveric population would produce a higher frequency of ligamentous injury without bone fracture. A difference in foot fixation in the current literature was also thought to influence the mode of soft tissue injury. The results documented isolated ligamentous injury to the posterior talofibular ligament and the 101 anterior portion of the deltoid ligament. The higher incidence of deltoid injuries when the foot was taped may indicate that the amount of constraint offered by shoes could influence the potential for and location of soft tissue injury in the ankle during external rotation. Chapter 5 detailed the development of a biofidelic ankle that can be used to predict the risk of ankle injury as a result of foot fixation on a playing surface. The biofidelic surrogate not only measures peak torque, but assesses the amount of rotational deformation that occurs at the ankle joint. Strain, unlike stress, may not be affected by strain rate. Thus, the surrogate’s ability to measure ankle rotation may be a more valuable predictor of soft tissue injury risk than peak torque alone. Additional experiments may be needed to validate this notion. Recommendations for Future Research: The research on ankle injury in this thesis evokes many questions about its impact on real-world injury situations. Additional ankle research using a paired study may be useful to address the potential injury issues that might be attributable to foot fixation and subtalar constraint. Constraining the cadaver foot/ankle complex in available footwear constructed with uppers of various rigidities may examine the real-world practicality of how foot mechanics (e. g. subtalar motion) may be restricted in certain models of shoes. The measurement of strain in the various ankle ligaments as a firnction of the rate of rotation and degree of constraint from shoe uppers is also important in understanding the mechanism and location of injury. Additional research may explain how these differences affect the body’s physiological response to foot fixation on a playing surface. 102 The data presented in this thesis provides a foundation for understanding the traction characteristics of third-generation, artificial surfaces. There is still much that remains unknown about their performance. The focus of the present work was in measuring rotational traction, under the assumption that excessive rotational traction produces an increased risk of lower extremity injury. There may always be a trade-off in artificial surface design between reducing rotational traction for increased “safety”, and increasing linear traction for improved speed and performance. In order to properly assess the relationship between rotational traction and linear traction, the measurement of linear traction on the tested surfaces in this thesis will be necessary. Future directions for rotational traction testing of shoe designs include documenting torque as a function of the center of rotation, and documenting how the torque may vary between an internally directed ground reaction torque and external ground reaction torque. Future directions for surface testing include measuring the effects of moisture and temperature on infill artificial surfaces. As manufacturers continue to update cleat and surface designs it is important to understand how specific variables affect traction characteristics with the ultimate goal of improving the shoe- surface interface by mitigating injury potential while maintaining or even improving player performance. The biofidelic ankle discussed in this thesis may provide an additional tool for assessment of the risk of ankle injury due to foot fixation on the playing surface. However, for this tool to be accepted it must be known if torque or rotation of the foot/ankle complex is a better measure of injury potential. The answer to this question may arise from ankle research that monitors the strain in the various ligaments during an 103 applied external rotation. The incorporation of a biofidelic knee into the surrogate lower extremity might also provide insight into determination of the “weakest link” under various shoe-surface interface conditions. It is not possible to fully evaluate the risk of injury on a surface without considering its hardness. The risk of concussion from head to surface impact represents a serious potential injury. Analysis of the deceleration forces associated with such collisions will provide another assessment of the relative risk of injury due to the player and surface interaction. The documentation of hardness values and traction characteristics provide quantitative measures for comparing the mechanical performance of the player-surface interface. An additional step is to study how these mechanical variations might translate into biomechanical differences in player movement patterns during sport specific maneuvers. This may provide for a clearer understanding of the specific injury mechanisms that can be associated with the football shoe-surface interface and aide in the development of future injury prevention technologies and training strategies. Through iterative shoe-surface designs and biomechanical testing, it may be possible to not only match the shoe-surface design to the sport, but match the shoe- surface interaction to the player. Continued research and development into understanding the complex behavior at the football shoe-surface interface may benefit the career and lives of athletes for years to come. 104 Appendix A: Peak torque, rotational stiffness and temperature data from Chapters 2 and 3 Table A1: Peak torque of Gameday Grass surfaces with cryogenic infill (Nm) Gameday Gameday Gameday Gameday Mfg Model Trial Fiber: MT Fiber: Tapex Fiber: XPe Fiber: SD Infill: Cryo Infill: Cryo Infill: Cgo Infill: Cryo 1 142 137 123 1 18 2 1 15 122 1 1 1 1 19 3 128 123 1 1 1 1 15 Nike B'a‘fig TD 4 120 123 119 116 Football 5 122 127 1 18 1 1 7 MEAN 125.5 126.4 116.4 117.0 SD 10.5 6.2 5.3 1 .6 TEMP 66°F 66°F 78°F 71°F 1 107 133 126 1 13 2 127 126 122 106 Vapor Jet 3 122 115 127 98 Nike TD 4 121 123 115 107 Low 5 121 120 124 100 Fotball MEAN 119.6 123.4 122.8 104.8 SD 7.5 6.7 4.8 6.0 TEMP 66°F 66°F 78°F 70°F 1 95 106 104 87 Air Zoom 2 104 98 99 104 Superbad 3 100 103 104 80 Nike Fl' 4 104 101 98 100 Mid 5 106 1 10 109 98 Football MEAN 101.8 103.6 102.8 93.8 SD 4.4 4.6 4.4 10.0 TEMP 66°F 66°F 78°F 74°F 1 99 107 94 88 2 102 1 10 96 85 'Air Zoom 3 106 100 95 80 Nike Blade D 4 93 101 96 89 Mld 5 101 107 92 93 Football MEAN 100.2 105.0 94.6 87.0 SD 4.8 4.3 1 .7 4.8 TEMP 66°F 66°F 78°F 70°F 1 77 79 89 87 2 69 90 85 94 Turf Hog 3 7o 93 92 96 . LE 4 70 84 87 84 ““133 Mid 5 71 95 84 90 Football MEAN 71.4 88.2 87.4 90.2 SD 3.2 6.6 3.2 4.9 TEMP 68°F 66°F 59°F 70°F 105 Table A2: Peak torque of Gameday Grass surfaces with cryogenic infill continued (Nm) Gameday Gameday Gameday Gameday Mfg Model Trial Fiber: MT Fiber: Tapex Fiber: XPe Fiber: 3D Infill: Cryo Infill: Cgo Infill: Cryo Infill: Cryo 1 117 124 128 108 2 117 123 132 105 Corner 3 121 129 129 102 . Blitz7D 4 122 130 119 105 Ad'das Mid 5 118 116 122 102 Football MEAN 119.0 124.4 126.0 104.4 so 2.3 5.6 5.3 2.5 TEMP 68°F 66°F 59°F 70°F 1 120 123 116 121 2 121 124 141 111 Scorch 3 123 117 120 116 . TRX 4 123 130 114 121 Ad'das Low 5 119 126 114 122 Football MEAN 121.2 124.0 121.0 118.2 so 1.8 4.7 11.4 4.7 TEMP 68°F 66°F 71°F 70°F 1 114 116 106 101 2 127 123 110 109 Scorch7 3 108 116 110 110 . Fly 4 105 116 113 105 Ad'das Low 5 117 112 122 113 Football MEAN 114.2 116.6 112.2 107.6 so 8.6 4.0 6.0 4.7 TEMP 68°F 66°F 71°F 70°F 1 104 109 108 104 2 115 119 119 114 Gridiron 3 111 116 120 103 . . 4 111 122 113 98 Adidas Mld Football 5 119 117 131 102 MEAN 112.0 116.6 118.2 104.2 so 5.6 4.8 8.6 5.9 TEMP 59°F 64°F 59°F 70°F 1 105 100 95 83 2 105 95 106 96 Quickslant 3 97 100 96 95 . D 4 112 113 93 91 Ad'das Mid 5 109 108 111 110 Football MEAN 105.6 103.2 100.2 95.0 so 5.6 7.2 7.9 9.8 TEMP 59°F 64°F 71°F 70°F 106 Table A3: Peak torque of Gameday Grass surfaces with extruded infill (Nm) Gameday Gameday Gameday Gameday Mfg Model Trial Fiber: MT Fiber: Tapex Fiber: XPe Fiber: 30 Infill: Ext. Infill: Ext. Infill: Ext. Infill: Ext. 1 1 13 109 1 10 106 2 105 104 107 107 BladeIITD 3 119 98 120 106 Nike Mid 4 116 101 117 99 Football 5 132 1 1 3 1 13 93 MEAN 117.0 105.0 113.4 102.2 SD 9.9 6.0 5.2 6.1 TEMP 89°F 97°F 84°F 91°F 1 1 17 99 1 17 108 2 102 100 1 18 105 Vapor Jet 3 113 107 111 103 Nike TD 4 111 119 105 102 Low 5 109 109 103 105 Fotball MEAN 110.4 106.8 110.8 104.6 SD 5.5 8.1 6.8 2.3 TEMP 89°F 97°F 84°F 91 °F 1 104 95 96 101 Air Zoom 2 89 91 97 95 Su pe rb ad 3 106 94 95 93 Nike Fl' 4 90 94 94 92 Mid 5 102 91 94 84 Football MEAN 98.2 93.0 95.2 93.0 SD 8.1 1 .9 1 .3 6.1 TEMP 89°F 97°F 84°F 97°F 1 88 95 95 109 2 92 90 95 86 Air Zoom 3 92 86 89 98 Nike Blade D 4 88 95 89 87 Mid 5 98 84 89 102 Football MEAN 91.6 90.0 91 .4 96.4 SD 4.1 5.0 3.3 9.9 TEMP 89°F 97°F 84°F 97°F 1 72 77 84 80 2 66 79 84 84 Turf H09 3 70 81 80 84 . LE 4 72 83 89 84 ““135 Mid 5 70 81 83 91 Football MEAN 70.0 80.2 84.0 84.6 SD 2.4 2.3 3.2 4.0 TEMP 89°F 91°F 86°F 89°F 107 Table A4: Peak torque of Gameday Grass surfaces with extruded infill continued (Nm) Gameday Gameday Gameday Gameday Mfg Model Trial Fiber: MT Fiber: Tapex Fiber: XPe Fiber: 3D Infill: Ext. InfiILExt. Infill: Ext; Infill: E_xt. 1 102 105 114 105 2 97 110 110 107 Corner 3 97 102 107 107 . Blitz7D 4 99 104 108 106 ““135 Mid 5 96 98 105 103 Football MEAN 98.2 103.8 108.8 105.6 so 2.4 4.4 3.4 1.7 TEMP 89°F 91°F 86°F 97°F 1 117 109 105 103 2 100 104 108 94 Scorch 3 106 98 96 100 . TRX 4 106 101 100 97 Ad'das Low 5 100 113 103 97 Football MEAN 105.8 105.0 102.4 98.2 so 6.9 6.0 4.6 3.4 TEMP 89°F 91°F 88°F 89°F 1 105 110 100 92 2 108 109 107 110 Scorch 7 3 96 92 92 97 . Fly 4 89 91 100 85 ““133 Low 5 88 97 87 101 Football MEAN 97.2 99.8 97.2 97.0 so 9.1 9.1 7.8 9.4 TEMP 89°F 91°F 88°F 89°F 1 90 105 98 93 2 97 103 100 100 . 3 89 100 99 103 Adidas Gnfiigm 4 90 95 105 107 Footba" 5 89 105 101 107 MEAN 91.0 101.6 100.6 102.0 so 3.4 4.2 2.7 5.8 TEMP 89°F 97°F 86°F 89°F 1 93 - 89 89 81 2 87 95 80 83 Quickslant 3 93 85 86 81 . o 4 97 84 87 88 Ad'das Mid 5 92 89 75 92 Football MEAN 92.4 88.4 83.4 85.0 so 3.6 4.3 5.8 4.8 TEMP 89°F 97°F 86°F 97°F 108 Table A5: Peak tOI'CBJC of Gameday Grass surfaces with ambient infill (Nm) _f ...r-h£ Gameday Gameday Gameday Gameday Mfg Model Trial Fiber: MT Fiber: Tapex Fiber: XPe Fiber: 3D Infill: Amb. Infill: Amb. Infill: Amb. Infill: Amb. 1 130 1 14 103 1 1 1 2 141 120 121 1 12 3 124 120 1 16 106 Nike slam: TD 4 114 121 107 108 Football 5 131 128 117 117 MEAN 128.0 120.6 112.8 110.8 SD 9.9 5.0 7.5 4.2 TEMP 75°F 90°F 81°F 86°F 1 124 128 120 105 2 1 15 1 13 107 94 Vapor Jet 3 123 120 108 91 Nike TD 4 1 16 120 1 16 97 Low 5 122 123 101 105 Fotball MEAN 120.0 120.8 1 10.4 98.4 SD 4.2 5.4 7.6 6.4 TEMP 66°F 90°F 81°F 88°F 1 96 90 109 91 Air Zoom 2 102 97 95 89 Superb a d 3 86 98 92 84 Nike FT 4 98 92 94 93 Mid 5 102 94 98 93 Football MEAN 96.8 94.2 97.6 90.0 SD 6.6 3.3 6.7 3.7 TEMP 66°F 90°F 81°F 88°F 1 96 106 92 93 2 97 101 82 78 Air Zoom 3 84 94 92 93 Nike Blade D 4 102 101 91 87 Mld 5 96 97 101 80 Football MEAN 95.0 99.8 91 .6 86.2 SD 6.6 4.5 6.7 7.0 TEMP 66°F 90°F 81°F 86°F 1 73 84 82 79 2 80 82 92 74 Turf H09 3 76 78 82 73 . LE 4 70 75 88 72 Ad'das Mid 5 77 79 78 77 Football MEAN 75.2 79.6 84.4 75.0 SD 3.8 3.5 5.5 2.9 TEMP 75°F 90°F 81°F 86°F 109 .7.— _.flafi'l‘l. Pfi‘b 17].”. ts- Table A6: Peak torque of Gameday Grass surfaces with ambient infill continued (Nm) Gameday Gameday Gameday Gameday Mfg Model Trial Fiber: MT Fiber: Tapex Fiber: XPe Fiber: 3D Infill: Amb. Infill: Amb. Infill: Amb. Infill: Amb. 1 1 10 1 15 103 100 2 102 104 108 100 Corner 3 109 107 109 107 . Blitz 7 D 4 100 100 103 97 Ad'das Mid 5 105 102 108 95 Football MEAN 105.2 105.6 106.2 99.8 SD 4.3 5.9 2.9 4.5 TEMP 77°F 85°F 81°F 86°F 1 102 1 12 102 103 2 102 1 1 1 1 14 1 17 Scorch 3 117 112 102 123 . TRX 4 1 1 7 107 102 1 17 “"135 Low 5 100 104 107 105 Football MEAN 107.6 109.2 105.4 1 13.0 SD 8.6 3.6 5.3 8.6 TEMP 77°F 90°F 83°F 86°F 1 1 1 1 109 109 81 2 1 13 1 1 1 101 84 Scorch 7 3 108 103 90 85 . Fly 4 1 17 94 100 82 Ad'das Low 5 111 107 110 95 Football MEAN 1 12.0 104.8 102.0 85.4 SD 3.3 6.7 8.1 5.6 TEMP 77°F 85°F 83°F 86°F 1 96 98 107 88 2 93 . 99 100 91 Grid Iron 3 92 99 109 103 Adidas Mid 4 97 "1 94 96 Football 5 100 101 115 95 MEAN 95.6 101.6 105.0 94.6 SD 3.2 5.4 8.2 5.7 TEMP 77°F 85°F 81°F 86°F 1 96 95 88 83 2 97 85 87 83 Quickslant 3 95 87 92 89 . D 4 89 97 91 82 Ad'das Mid 5 86 90 88 90 Football MEAN 92.6 90.8 89.2 85.4 SD 4.8 5.1 2.2 3.8 TEMP 77°F 85°F 81°F 86°F 110 .._ .... _.. Table A7 : Peak torque of FieldTurf, AstroPlay, and natural grass surfaces (Nm) ..h..e-—- --. AstroPlay Field Turf Practice Stadium Mfg Model Trial MSU UM Grass Grass Indoor Indoor (Native Soil) (Sand Soil) 1 1 13 125 94 108 2 135 132 84 1 17 3 1 19 147 81 1 1 1 Nike Blatfilj TD 4 118 136 80 121 Football 5 123 139 99 121 MEAN 121.6 135.8 87.6 115.6 SD 8.3 8.2 8.4 5.9 TEMP 70°F 70°F 90°F 52°F 1 1 19 130 88 99 2 1 15 130 103 99 Vapor Jet 3 109 130 101 98 Nike TD 4 120 133 100 111 Low 5 129 135 101 95 Fotball MEAN 1 18.4 131.6 98.6 100.4 SD 7.3 2.3 6.0 6.1 TEMP 70°F 70°F 90°F 52°F 1 123 1 18 69 104 . 2 1 17 126 76 102 £33); 3 120 120 77 103 Nike FT 4 1 15 1 12 78 105 Mid 5 124 1 1 1 68 93 Football MEAN 119.8 117.4 73.6 101.4 SD 3.8 6.1 4.7 4.8 TEMP 70°F 70°F 90°F 52°F 1 122 121 81 130 2 135 1 17 81 100 AirZoom 3 135 114 85 112 Nike Blade D 4 126 127 83 102 Mid 5 136 1 19 85 1 18 Football MEAN 130.8 119.6 83.0 112.4 SD 6.4 4.9 2.0 12.3 TEMP 70°F 70°F 90°F 52°F 1 77 82 63 62 2 72 78 60 57 Turf H09 3 78 79 55 56 . LE 4 82 88 60 58 ““138 Mid 5 83 80 62 65 Football MEAN 78.4 81 .4 60.0 59.6 SD 4.4 4.0 3.1 3.8 TEMP 70°F 70°F 90°F 52°F 111 Table A8: Peak torque of AstroPlay, F ieldTurf,and natural grass surfaces continued (Nm) AstroPlay Field Turf Practice Stadium Mfg Model Trial MSU UM Grass Grass Indoor Indoor (Native Soil) (Sand Soil) 1 107 124 85 77 2 108 1 18 73 71 Corner 3 108 120 83 70 . Blitz 7 D 4 107 124 74 79 Ad'das Mid 5 116 123 74 74 Football MEAN 109.2 121.8 77.8 74.2 SD 3.8 2.7 5.7 3.8 TEMP 70°F 70°F 90°F 52°F 1 1 19 133 80 99 2 128 1 18 81 105 Scorch 3 1 13 133 69 97 . TRX 4 1 15 125 88 100 Ad'das Low 5 110 136 81 92 Football MEAN 117.0 129.0 79.8 98.6 SD 7.0 7.4 6.8 4.7 TEMP 70°F 70°F 88°F 52°F 1 115 124 88 110 2 108 120 98 102 Search 7 3 102 120 94 121 . Fly 4 109 1 18 90 108 Ad'das Low 5 105 120 105 96 Football MEAN 107.8 120.4 95.0 107.4 SD 4.9 2.2 6.8 9.4 TEMP 70°F 70°F 88°F 52°F 1 106 104 83 86 2 1 14 1 11 84 94 Grid Iron 3 117 113 87 83 . . 4 104 1 17 82 82 Adidas Mld Football 5 107 117 71 79 MEAN 109.6 112.4 81.4 84.8 SD 5.6 5.4 6.1 5.7 TEMP 70°F 70°F 90°F 52°F 1 102 1 16 96 102 2 1 12 108 96 107 Quickslant 3 1 08 1 1 3 92 102 . D 4 1 1 1 1 10 105 108 Ad'das Mid 5 96 120 83 104 Football MEAN 105.8 113.4 94.4 104.6 SD 6.7 4.8 8.0 2.8 TEMP 70°F 70°F 90°F 52°F 112 Table A9: Rotational stiffness of Gameday Grass surfaces with cryogenic infill (Nm/de ee Gameday Gameday Gameday Gameday Mfg Model Trial Fiber: MT Fiber: Tapex Fiber: XPe Fiber: 30 Infill: Cryo Infill: Cryo Infill: Cryo Infill: Cryo 1 4.29 3.07 3.28 3.26 2 2.71 4.01 4.02 2.71 3 4.29 4.28 3.72 3.32 Nike Bla‘fi’igm 4 3.88 4.48 3.83 2.37 Football 5 3.65 3.96 2.92 3.08 MEAN 3.8 4.0 3.6 2.9 SD 0.7 0.5 0.4 0.4 TEMP 66°F 66°F 78°F 71°F 1 2.79 3.26 3.13 3.07 2 3.48 3.16 3.50 2.61 Vapor Jet 3 3.14 3.06 2.97 2.79 Nike TD 4 3.24 3.11 3.14 3.10 Low 5 3.26 2.77 3.36 3.11 Fotball MEAN 3.2 3.1 3.2 2.9 SD 0.3 0.2 0.2 0.2 TEMP 66°F 66°F 78°F 70°F 1 2.67 2.46 3.02 2.06 . 2 2.40 3.27 2.57 2.18 £3,332! 3 2.22 2.18 2.32 1.63 Nike FT 4 2.96 2.38 2.79 2.70 Mid 5 2.76 1.99 3.05 1.86 Football MEAN 2.6 2.5 2.8 2.1 SD 0.3 0.5 0.3 0.4 TEMP 66°F 66°F 78°F 74°F 1 3.44 3.05 2.44 2.06 2 3.33 4.62 3.55 2.48 Air Zoom 3 3.30 3.66 3.12 1.34 Nike BladeD 4 3.28 4.61 4.19 2.12 Mid 5 3.22 4.30 3.37 3.90 Football MEAN 3.3 4.1 3.3 2.4 SD 0.1 0.7 0.6 0.9 TEMP 66°F 66°F 78°F 70°F 1 3.88 2.76 3.70 3.06 2 4.29 3.63 3.02 3.39 Turf H09 3 4.32 3.76 2.21 3.08 . LE 4 2.68 3.17 3.71 3.86 ““135 Mid 5 4.53 3.64 2.97 3.56 Football MEAN 3.9 3.4 3.1 3.4 SD 0.7 0.4 0.6 0.3 TEMP 68°F 66°F 59°F 70°F 113 Table A10: Rotational stiffness of Gameday Grass surfaces with cryogenic infill continued (N m/degree) Gameday Gameday Gameday Gameday Mfg Model Trial Fiber: MT Fiber: Tapex Fiber: XPe Fiber: 3D Infill: Cryo Infill: Cryo Infill: Cryo Infill: Cryo 1 4.26 3.98 4.63 3.71 2 5.40 4.87 5.28 3.58 Comer 3 5.32 4.83 4.68 4.26 . Blitz 7 D 4 5.35 5.28 5.55 4.27 ““135 Mid 5 5.32 4.19 4.76 4.76 Football MEAN 5.1 4.6 5.0 4.1 SD 0.5 0.5 0.4 0.5 TEMP 68°F 66°F 59°F 70°F 1 3.35 3.31 2.91 2.71 2 3.63 3.28 3.65 2.48 Scorch 3 3.70 3.77 3.39 3.21 . TRX 4 3.07 3.23 2.89 2.95 ““135 Low 5 3.17 3.23 3.77 3.10 Football MEAN 3.4 3.4 3.3 2.9 SD 0.3 0.2 0.4 0.3 TEMP 68°F 66°F 71°F 70°F 1 3.20 2.90 4.56 2.94 2 3.97 3.36 3.27 2.92 Scorch 7 3 4.42 3.53 3.67 3.90 . Fly 4 3.50 3.39 3.72 3.14 ““135 Low 5 4.68 3.74 4.23 4.04 Football MEAN 4.0 3.4 3.9 3.4 SD 0.6 0.3 0.5 0.5 TEMP 68°F 66°F 71 °F 70°F 1 3.88 3.79 4.06 3.58 2 4.80 4.45 4.80 4.29 . 3 5.49 4.50 4.32 4.78 Adidas Graig“ 4 4.52 4.78 3.29 4.21 Football 5 4.97 4.91 2.94 4.29 MEAN 4.7 4.5 3.9 4.2 SD 0.6 0.4 0.8 0.4 TEMP 59°F 64°F 59°F 70°F 1 2.19 3.77 3.00 2.61 2 4.02 3.39 4.20 2.80 Quickslant 3 3.65 3.40 2.47 1 .88 . D 4 2.95 4.15 2.27 1.82 Ad'das Mid 5 3.80 3.75 2.95 1.83 Football MEAN 3.3 3.7 3.0 2.2 SD 0.8 0.3 0.8 0.5 TEMP 59°F 64°F 71°F 70°F 114 Table All: Rotational stiffness of Gameday Grass surfaces with extruded infill (Nm/degree) Gameday Gameday Gameday Gameday Mfg Model Trial Fiber: MT Fiber: Tapex Fiber: XPe Fiber: 3D Infill: Ext. Infill: Ext. Infill: Ext. Infill: Ext. 1 3.51 2.93 3.20 2.43 2 4.17 3.68 3.92 2.77 3 3.60 3.28 3.90 3.08 Nike mats TD 4 4.21 3.36 4.10 3.19 Football 5 3.50 2.99 4.08 3.51 MEAN 3.8 3.2 3.8 3.0 SD 0.4 0.3 0.4 0.4 TEMP 89°F 97°F 84°F 91 °F 1 3.44 2.26 3.65 2.84 2 3.84 2.92 3.24 3.06 Vapor Jet 3 3.10 2.82 3.30 2.86 Nike TD 4 3.19 2.84 3.34 3.01 Low 5 3.74 3.44 2.93 2.50 Fotball MEAN 3.5 2.9 3.3 2.9 SD 0.3 0.4 0.3 0.2 TEMP 89°F 97°F 84°F 91 °F 1 2.22 2.93 2.06 2.29 . 2 1.93 2.26 1.88 1.66 99%;); 3 2.26 2.80 2.04 2.05 Nike FT 4 2.43 2.25 2.00 2.11 Mid 5 2.20 2.28 2.18 2.25 Football MEAN 2.2 2.5 2.0 2.1 SD 0.2 0.3 0.1 0.3 TEMP 89°F 97°F 84°F 97°F 1 3.40 2.99 3.03 2.93 2 4.45 1.61 2.21 3.33 Air Zoom 3 3.77 2.95 3.96 2.16 Nike Blade D 4 3.08 3.13 3.44 1.93 Mid 5 3.58 3.54 2.92 1.82 Football MEAN 3.7 2.8 3.1 2.4 SD 0.5 0.7 0.6 0.7 TEMP 89°F 97°F 84°F 97°F 1 2.90 2.82 2.90 3.10 2 3.30 2.88 2.98 3.46 Turf Hog 3 2.42 3.27 3.39 3.31 . LE 4 2.80 2.70 3.68 2.86 Ad'das Mid 5 3.28 2.72 3.50 4.24 Football MEAN 2.9 2.9 3.3 3.4 SD 0.4 0.2 0.3 0.5 TEMP 89°F 91 °F 86°F 89°F 115 Table A12: Rotational stiffness of Gameday Grass surfaces with extruded infill continued (Nut/degree) Gameday Gameday Gameday Gameday Mfg Model Trial Fiber: MT Fiber: Tapex Fiber: XPe Fiber: 3D lnfilgxt. Infill: Ext. Infill: gxt. Infill: Ext. 1 3.30 3.44 3.71 3.63 2 3.92 4.29 3.82 4.49 Corner 3 3.87 4.15 3.73 4.85 . Blitz7D 4 3.75 3.81 3.86 3.88 ““135 Mid 5 3.78 4.40 4.03 4.38 Football MEAN 3.7 4.0 3.8 4.2 so 0.2 0.4 0.1 0.5 TEMP 89°F 91°F 86°F 97°F 1 2.44 2.15 2.74 2.73 2 2.70 2.28 3.51 2.50 Scorch 3 1 .97 2.95 3.26 2.72 . TRX 4 2.28 2.35 3.76 2.64 Ad'das Low 5 2.58 2.49 3.22 2.86 Football MEAN 2.4 2.4 3.3 2.7 so 0.3 0.3 0.4 0.1 TEMP 89°F 91°F 88°F 89°F 1 2.81 4.05 3.24 2.98 2 3.51 3.41 3.86 3.09 Scorch7 3 3.14 3.55 4.27 3.30 . Fly 4 3.54 3.26 3.51 3.30 Ad'das Low 5 3.86 3.48 3.92 3.63 Football MEAN 3.4 3.5 3.8 3.3 so 0.4 0.3 0.4 0.3 TEMP 89°F 91°F 88°F 89°F 1 3.32 3.73 3.99 3.36 2 4.86 3.72 4.91 4.23 . 3 4.72 3.58 4.35 4.17 Adidas Graig“ 4 4.28 3.76 4.36 3.90 Footba" 5 3.49 4.31 4.45 3.59 MEAN 4.1 3.8 4.4 3.9 so 0.7 0.3 0.3 0.4 TEMP 89°F 97°F 86°F 89°F 1 3.47 2.44 3.10 3.31 2 2.95 2.66 1.78 2.55 Quickslant 3 2.08 2.78 3.14 3.10 . o 4 1.76 2.86 3.18 1.76 “"135 Mid 5 4.37 2.61 2.95 1.92 Football MEAN 2.9 2.7 2.8 2.5 so 1.1 0.2 0.6 0.7 TEMP 89°F 97°F 86°F 97°F 116 Table A13: Rotational stiffness of Gameday Grass surfaces with ambient infill (Nm/degree) Gameday Gameday Gameday Gameday Mfg Model Trial Fiber: MT Fiber: Tapex Fiber: XPe Fiber: 30 Infill: Amb. Infill: Amb. infill: Amb. infill: Amb. 1 3.24 3.18 2.51 2.77 2 3.62 3.35 3.04 2.35 3 3.64 3.20 3.10 3.15 Nike Elam: TD 4 3.48 3.49 3.57 3.59 Footba" 5 3.66 3.52 3.98 2.52 MEAN 3.5 3.3 3.2 2.9 so 0.2 0.2 0.6 0.5 TEMP 75°F 90°F 81°F 86°F 1 3.22 3.88 2.70 2 3.19 3.31 2.67 Vapor Jet 3 3.43 2.65 2.62 Nike TD 4 .77; 3.71 3.80 2.60 Low 5 , 3 3.55 3.60 2.13 Fotball MEAN :9, 3.4 3.4 2.5 so 8 0.2 0.5 0.2 TEMP g 90°F 81°F 88°F 1 .g 2.15 2.32 2.24 AirZoom 2 g 1.96 2.50 2.10 Superbad! 3 g; 2.18 2.08 1.75 Nike FT 4 g 2.88 2.12 1.89 Md 5 g 2.09 2.24 1.86 Footba" MEAN g 2.3 2.3 2.0 so as 0.4 0.2 0.2 TEMP f, 90°F 81°F 88°F 1 5 3.32 3.06 2.06 2 E 3.78 3.07 3.20 Air Zoom 3 b 3.20 3.14 1.78 Nike BladeD 4 g 3.74 3.39 2.35 Mld , 5 w a: 2.81 2.91 1.77 Football MEAN 3.4 3.1 2.2 , so . 0.4 0.2 0.6 TEMP 90°F 81°F 86°F 1 2.98 3.07 2.88 2.34 2 3.43 3.13 2.64 3.02 Turf H09 3 3.05 3.34 3.15 2.55 . LE 4 3.07 3.51 3.28 3.28 ““133 Mid 5 Data Lost 3.48 2.83 2.79 Football MEAN 3.1 3.3 3.0 2.8 so 0.2 0.2 0.3 0.4 TEMP 75°F 90°F 81°F 86°F 117 Table A14: Rotational stiffiiess of Gameday Grass surfaces with ambient infill continued film/degree) Gameday Gameday Gameday Gameday Mfg Model Trial Fiber: MT Fiber: Tapex Fiber: XPe Fiber: 30 Infill: Amb. Infill: Amb. Infill: Amb. Infill: Amb. 1 4.83 3.31 3.19 3.45 2 4.84 3.26 3.60 3.84 Corner 3 4.35 3.59 4.03 3.36 . Blitz7D 4 4.50 2.90 3.24 3.19 Ad'das Mid 5 3.29 3.68 3.80 3.40 Football MEAN 4.4 3.3 3.6 3.4 so 0.6 0.3 0.4 0.2 TEMP 77°F 85°F 81°F 86°F 1 2.61 2.98 1.76 2.52 2 2.39 2.86 3.63 2.87 Scorch 3 2.99 3.00 2.86 2.77 . TRX 4 2.40 3.41 3.28 2.04 Ad'das Low 5 3.03 2.74 3.29 3.01 Football MEAN 2.7 3.0 3.0 2.6 so 0.3 0.3 0.7 0.4 TEMP 77°F 90°F 83°F 86°F 1 3.18 3.10 2.75 3.06 2 3.31 4.01 3.70 3.31 Scorch7 3 3.37 3.91 3.47 1.81 . Fly 4 3.59 3.66 3.35 3.66 Ad'das Low 5 3.90 3.22 3.35 2.69 Football MEAN 3.5 3.6 3.3 2.9 so 0.3 0.4 0.4 0.7 TEMP 77°F 85°F 83°F 86°F 1 3.21 3.06 3.98 2.70 2 4.03 3.90 4.72 3.65 . 3 4.14 3.55 3.59 3.65 Adidas Graig” 4 3.59 4.18 3.50 3.39 Footba" 5 4.61 3.34 4.48 3.48 MEAN 3.9 3.6 4.1 3.4 so 0.5 0.4 0.5 0.4 TEMP 77°F 85°F 81°F 86°F 1 2.39 3.03 2.82 2.57 2 1.89 3.67 2.40 3.01 Quickslant 3 2.26 3.32 3.50 1.93 . o 4 1.79 2.51 1.78 1.90 Ad'das Mid 5 2.19 3.43 2.87 2.99 Football MEAN 2.1 3.2 2.7 2.5 so 0.3 0.4 0.6 0.5 TEMP 77°F 85°F 81°F 86°F 118 Table A15: Rotational stiffness of AstroPlay, FieldTurf, and natural grass surfaces (Nm/degree) AstroPlay Field Turf Practice Stadium Mfg Model Trial MSU UM Grass Grass Indoor Indoor (Native Soil) JSand Soil) 1 3.37 3.46 1.65 1.97 2 2.89 3.89 1.61 2.23 3 4.04 4.10 1.77 2.07 Nike B'afig TD 4 2.96 3.97 1.38 2.48 Footba" 5 2.85 4.35 1.85 2.24 MEAN 3.2 4.0 1.7 2.2 so 0.5 0.3 0.2 0.2 TEMP 70°F 70°F 70°F 70°F 1 3.12 3.61 1.71 2.24 2 3.63 4.50 2.43 1.86 Vapor Jet 3 3.64 3.94 1 .98 3.00 Nike TD 4 3.81 3.72 1.99 2.14 Low 5 3.76 4.13 1.97 2.24 Fotball MEAN 3.6 4.0 2.0 2.3 so 0.3 0.4 0.3 0.4 TEMP 70°F 70°F 70°F 70°F 1 2.59 2.53 1.60 1.58 . 2 2.25 2.15 1.60 1.81 3;":va 3 2.31 2.26 1.42 1.55 Nike FT 4 2.34 2.71 1.41 1.92 Mid 5 2.27 2.78 1.16 1.76 Football MEAN 2.4 2.5 1.4 1.7 so 0.1 0.3 0.2 0.2 TEMP 70°F 70°F 70°F 70°F 1 4.03 2.86 1.57 2.70 2 3.20 2.58 2.90 3.32 AirZoom 3 2.57 3.11 3.10 2.39 Nike BladeD 4 4.12 3.31 1.93 3.21 Mid 5 2.87 3.65 2.03 2.79 Football MEAN 3.4 3.1 2.3 2.9 so 0.7 0.4 0.7 0.4 TEMP 70°F 70°F 70°F 70°F 1 3.26 2.81 1.83 2.17 2 3.37 3.17 2.35 1.29 Turf Hog 3 3.37 2.97 2.01 1.43 . LE 4 3.31 3.24 3.37 1.72 “"135 Mid 5 3.49 3.10 1.56 1.47 Football MEAN 3.4 3.1 2.2 1.6 so 0.1 0.2 0.7 0.3 TEMP 70°F 70°F 70°F 70°F 119 Table A16: Rotational stiffness of AstroPlay, FieldTurf, and natural grass surfaces continued (Nm/degree) AstroPlay Field Turf Practice Stadium Mfg Model Trial MSU UM Grass Grass Indoor Indoor (Native Soil) (Sand Soil) 1 3.91 4.23 2.92 2.53 2 4.86 5.42 3.87 2.45 Corner 3 4.26 5.30 2.28 2.76 Adidas Blitz.7 D 4 4.38 5.10 3.08 2.22 Mid 5 4.32 5.37 4.07 2.79 Football MEAN 4.3 5.1 3.2 2.5 SD 0.3 0.5 0.7 0.2 TEMP 70°F 70°F 70°F 70°F 1 2.83 2.99 2.05 2.02 2 3.21 2.94 2.03 2.08 Scorch 3 3.14 3.05 2.04 2.06 Adidas TRX 4 3.16 3.05 2.41 1.66 Low 5 3.44 2.99 2.76 2.02 Football MEAN 3.2 3.0 2.3 2.0 SD 0.2 0.0 0.3 0.2 TEMP 70°F 70°F 70°F 70°F 1 3.01 3.62 2.02 1.62 2 3.97 3.63 2.36 2.08 Scorch 7 3 4.47 3.79 1.77 2.46 . Fly 4 3.72 3.52 2.18 2.11 Ad'das Low 5 3.66 3.92 1.68 1.64 Football MEAN 3.8 3.7 2.0 2.0 SD 0.5 0.2 0.3 0.4 TEMP 70°F 70°F 70°F 70°F 1 3.75 3.43 3.16 1.97 2 4.33 4.09 2.06 2.88 Grid Iron 3 4.67 4.83 1.84 1.84 Adidas Mid 4 4.31 4.37 2.21 2.86 Football 5 4.53 4.16 2.55 2.75 MEAN 4.3 4.2 2.4 2.5 SD 0.4 0.5 0.5 0.5 TEMP 70°F 70°F 70°F 70°F 1 3.45 3.34 2.36 2.63 2 2.47 3.61 1.60 3.40 Quickslant 3 3.35 3.24 2.81 2.22 Adidas D 4 3.52 3.66 3.55 2.34 Mid 5 3.69 3.08 1.99 3.09 Football MEAN 3.3 3.4 2.5 2.7 SD 0.5 0.2 0.8 0.5 TEMP 70°F 70°F 70°F 70°F 120 Appendix B: Standard operating procedure for measurement of rotational traction on the football shoe—surface interface. Purpose: The purpose of the torsional traction test is to measure the traction properties between footwear and ground surfaces. *Prescripts of A & B denote responsibilities of each person* Shoes: 1. All shoes must be size 13 mens unless more lasts are made. 2. B Each shoe is to be put on the manikin foot and tied very tightly. 3. B Shoe laces should he seemed away from the ground-shoe interface. Pre-Test Setup: 1. Unpack the tester 3. Position the tester over the first test site b. A Unhitch the trailer mover c. B Lean the tester toward the hitch d. A Remove the pins holding on the rear wheel assembly 6. B Set the tester back down 2. A Hook upthe computer using the A2D board. 3. Zero the torque sensor. 121 Prior to First Test: 1. Suspend a known weight from the pulley. 2. Document the live readout from the load cell. 3. Ensure that the load cell is reading the proper torque. Torque = Force*Moment Arm = Weight(in Newtons)*0.25m 4. If there is a discrepancy, the load cell must be replaced before testing as it is damaged. First Test Setup: 1. Attach the top of the manikin leg to the plate under the plexi-glass disk allowing for desired rotation. 8. Attach directly above the heel if heel rotation is desired, likewise above the forefoot if forefoot rotation is desired. B Attach the 95 pounds of weights to the cable. . Feed the cable around the plexi-glass disk. A Pull the height lever back so the cable is even with the pulley. B Use the leverage bar to cock the disk until the release latch holds it in place. B When the weights are elevated the foam pad should be placed below them to prevent ground damage. The shoe should now be pointing straight forward. A Carefully lower the apparatus until the weight is completely on the shoe. 8. A Both the height lever and release lever are adjusted at the same time. 122 9. Once the test is ready to start, both testers should be standing with both feet on the fold down pads. 10. A The computer record program should be started and the release lever pulled to run the test. Following Test Setups: 1. A Pull the height lever back so the cable is even with the pulley. 2. B Use the leverage bar to cock the disk until the release latch holds it in place. 3. B Lean the tester toward the hitch and use your feet to place the leverage bar under the tester. 4. B Set the tester back down 5. A Using the trailer mover, lift the hitch end and slide 14-18 inches toward the hitch. a. B The tester should be balanced on the leverage bar while sliding. 6. B Lean the tester toward the hitch and remove the leverage bar from under the tester. 7. B Fully rotate the ankle back to the starting position by contacting the stop. 8. A Carefully lower the apparatus until the weight is completely on the shoe. 3. A Both the height lever and release lever are adjusted at the same time. 9. Once the test is ready to start, both testers should be standing with both feet on the fold down pads. 10. A The computer record program should be started and the release lever pulled to run the test. 123 11. Five tests are completed with each shoe/ground interface. After which either the shoe is changed or the tester is moved to another ground surface. Last Test Setup: 1. Suspend a known weight from the pulley 2. Document the live readout fi'om the load cell. 3. Ensure that the load cell is reading the proper torque. Torque = Force*Moment Arm = Weight(in Newtons)*0.3 3m 4. If there is a discrepancy, the data fiom the current day of testing must be discarded and the load cell replaced as it is damaged. Sofl‘ware Setup: 1. The labview program for the rotational traction test is called “NFL torsion for LV7.vi” 2. Pressing the play button on the top left of the screen will transfer the program to live mode. This will read the live data from the angular transducers and load cell. 3. The program is executed by pressing start. The digital trigger must be “disabled” for the start button to initiate the test. 4. The torque is measured in channel 1. The leg and ankle rotation are channels 2 and 3, respectively. 124 Play button ' pm Acquisitionqfllpyllqfl. . - 3 ”for Measurement OWE! 1. for live mode pcmcm-Dmém #20 Bud . _... "ll .1.: L....:;_ I- 66.67 .:. Live readout for selected channel Frequency of data collection can be changed here. This will collect at Button to start test 5000 Hz for 4 seconds. Click to disable . This IS necessary in order to begin test with “start” button Figure Bl: Live readout of the labview pro gram during a rotational traction test. Data Analysis: 1. For data analysis, refer to the separate SOP entitled “SOP_Traction_Analysis_Macro.doc” Things to remember during testing: 0 Do not test over grass with paint on it unless all of the tests are conducted that way. 125 Helpful tips for troubleshooting: 0 If the shoe isn’t going onto the manikin foot easily it is sometimes helpfiil to lift the other side of the tester with the trailer mover. 'Il'llilll “a“ .. . ..1. ‘0' ‘IT‘. "‘9'... {p - . a .1. . . P 1‘ ~ "~. I - ' ~ Height Lever !' S r—' "a Release Lever Fold Down Pads Figure B2: Key components of the rotational traction apparatus. 126 Appendix C: Standard operating procedure for analysis of rotational traction data The labview program “NFL torsion for LV7.vi” is used to collect data for a rotational traction experiment. Upon execution, the program generates a .csv file and subsequently, an excel file for each trial. One of the worksheets in the excel file is titled “data” and contains the data in columns A:H., For data analysis, a custom macro was created. The macro is entitled "Macro_FullAnalyses_NFL_Traction.xls”. This macro will calculate the peak torque during a trial, the stiffness to 75% of the peak torque, and the peak ankle rotation (cells W1 :3). In order to perform the data analysis, open the excel file which you wish to analyze, select the worksheet named “data”, then press ctrl + q to execute the macro. For the macro to execute, the original file containing the macro must be opened. This means that you must open “Macro_Ful1Analyses_NFL_Traction.xls” prior to performing the analysis. The code for the macro is included below. In addition, the macro can calculate the ankle rotation associated with a chosen torque value. The default is 72.5 Nm corresponding to the average failure torque of the NFL ankle cadaver tests performed in our laboratory, it can be changed by entering a new value in cell S6. It is unknown if this additional analysis provides any important information. It has been included for comparison purposes. 127 Macro Code Range("Il ").Select ActiveCell.FormulaRlC1 = "Torque < 3" Range("J 1").Select ActiveCell.FormulaRlC1 = "Torque < F ail" Range("Kl ").Select ActiveCell.FormulaRlC1 = "Torque < 75%PT" Range("Ll ").Select ActiveCell.FormulaRlC1 = "Leg < 85" Range("Ml ").Select ActiveCell.FormulaRlC1 = "Find 3" Range("Nl ").Select ActiveCell.FormulaRlC1 = "F ind Fail" Range(”Ol ").Select ActiveCell.FormulaRlC1 = "Find 75%PT" Range("Pl ").Select ActiveCell.FormulaRlC1 = "Find Leg85" Range("Rl ").Select ActiveCell.FormulaRlC1 = "Match 3Nm" Range("R2").Select ActiveCell.FormulaRlC1 = "Match Fail" Range("R3").Select ActiveCell.FormulaRlC1 = "Match 75%PT" 128 Range("R4").Selcct ActiveCell.FormulaRl C1 = "Match Leg85" Range("Vl ").Select ActiveCell.FormulaRl C1 = "Peak Torque" Range("Wl ").Select ActiveCell.FormulaRl C1 = "=MAX(R[1]C[-21]:(INDEX(C2,R4C19,0)))" Range("V2").Seleet ActiveCell.FormulaRlC1 = "Stiffness" Range("W2").Select ActiveCell.FormulaRlC1 = _ "=SLOPE((INDEX(C2,R1C19,0)):(INDEX(C2,R3C19,0)),(INDEX(C7,R1C19,0)):(IND EX(C7,R3C19,0)))" Range("12").Select Range("R6").Select ActiveCell.FormulaRl C1 = "Cadaver Failure Torque" Range("S6").Select ActiveCell.FormulaRl C1 = "75 " Range("12").Select ActiveCell.FormulaRl C1 = "=IF(RC[-7]<3 ,1,0)" Range("12").Select Selection.AutoFill Destination:=Range("I2:I10001 ") Range("12:110001").Select 129 Range("12").Select ActiveCell.FormulaRl C1 = "=IF(RC[-8] FibA = FootA = TalA = CalA = Output(TibA,FibA,FootA,TalA,CalA) 159 {*The translation of the fibula will be Centerfib and the translation of the tibia will be Centertib. The rotations of them will be TibA and FibA. Correct calibration and orientation of the Vicon system is important when determining medial-lateral, anterior- posterior translation as well as directions of rotation *} 160 Ankle_Center.mod {*Determine Tibia/Fibula Geometric Centers Using CT Displacements*} {*Ankle_Center.mod*} {*Usc with BodyBuilder*} {*Use with Ankle.mkr file*} {*Usc with Ankle.mp*} GOrigin = {0,0,0} Global = [Gorigin,{1,0,0},{0,0,1 },xyz] xaxis = {100,0,0} yaxis = {0,100,0} zaxis = {0,0,100} {*Start of macro section*} {* *} macro Substitute4(p1 ,p2,p3,p4) $234 = [p3,p2-p3,p3-p4] pr = Average(pl/6234)*s234 8341 = [P4,P3-P4,P4-P1] p2V = Average(p2/s34l)*s341 S412 = [p1,p4-p1,p1-p2] p3V = Average(p3/s412)*s412 161 s123 = [p2,pl-p2,p2-p3] p4V = Average(p4/s123)*s123 p1= (p1+p1V)/2 ? pl? pr p2 = (p2+p2V)/2 ? p2 ? p2V p3 = (p3+p3V)/2 ? p3 ? p3V p4 = (p4+p4V)/2 '2 p4 '2 p4V endmacro {*Create segrnents*} Fibula = [Fib1,(Fib2-Fib1),(zaxis-GOrigin),l ] Foot = [Footl ,(Foot2-Footl ),(zaxis-GOrigin), 1] Substitute4(Tall ,T312,Tal3 ,Tal4) Talus = [Tall,(Ta.12-Tall),(Tal4-Tal3),1] Output(Tal 1 ,T312,Tal3 ,Tal4) Substitute4(Tib1,Tib2,Tib3,Tib4) Tibia = [Tib1,Tib2-Tib1 ,Tib4-Tib3 ,1 ] Output(Tibl ,Tib2,Tib3 ,Tib4) Substitute4(Call ,C312,Cal3,Cal4) Calcaneous = [Call,(CalZ-Call),(Cal4-Cal3),1] Output(Call ,C312,Cal3,Cal4) {*Define Fibl and Tibl markers in local coords*} %Fibl = Fibl/Fibula %Tibl = Tibl/Tibia 162 {*Define tibia array fixture location using known fixed distance displacement from Tibl *} %FixT = {%Tibl(1)-32,%Tib1(2)+0,%Tib1(3)+0} FixT = %FixT*Tibia {*Define fibula and tibia center of rotation using global displacements from CT scan*} {*Go to the transverse slice in the CT that includes the array fixture for the Tibia or the F ibl marker for the fibula. Then calculate the anterior/posterior and medial/lateral displacement from the fixture/marker to the geometric center of the bone structure. This point will serve as the reference point for tibia/fibula translations. The displacements will be entered into the shaded boxes below.*} CORfib = {Fibl(1)+MFib1(2)-m,Fibl(3)+O} CORtib = {Fixm)flFixT(2)-fl,rixr(3)+0} %CORfib = CORfib/Fibula %CORtib = CORtib/Tibia {*Output COR for fib and tib wrt to segments. The initial coords can be input as displacements in Motions_Rotations.mod*} Output(%CORfib,%CORtib,CORfib,CORtib,FixT) 163 MICHI AN STATE UNIVERSITY LIBRARIES G I 3 1293 J3062 6489