The human thumb is necessary for the completion of daily tasks (e.g., driving, cooking), and accounts for 40% of overall hand function. However, the carpometacarpal (CMC) joint, located at the base of the thumb, has developed osteoarthritis (OA) in up to 50% of older individuals, with a preponderance among females. The associated symptoms of pain, weakness, and deformity have led to the inability to perform self-care, depression, and considerable financial burdens. Therefore, there is a pressing need to monitor the health and function of the thumb joints to track the onset, progression, and treatment of CMC OA. In cases of severe CMC OA, surgical intervention has been pursued. Numerous surgical techniques have been used to treat CMC OA, and have been effective in reducing patient pain. However, patients have reported dissatisfaction with thumb function after surgery, and currently there are limited approaches to compare post-operative outcomes across various interventions. Clinical tools are not able to capture the complex and dynamic abilities of the thumb, including its full range of motion and ability to generate force. Thus, there is a need for approaches to assess and monitor complete three-dimensional thumb motions and changes in force generation. This dissertation presents work in these areas. Chapter one is a review of the literature, and discusses thumb anatomy and its unique characteristics. The prevalence, impact, and treatment of CMC OA are identified. Chapter two discusses the methods used to quantify motion of the thumb metacarpal using motion capture marker-derived coordinate systems on the hand dorsum. Results showed statistically and clinically significant differences in angle ranges and errors between coordinate systems, highlighting the importance of careful coordinate system selection. Chapter three studies the kinematics of the thumb metacarpal and proximal phalange using a two-dimensional motion mapping in asymptomatic controls and CMC OA participants (tested pre-surgery, 3-month, and 6-months post-surgery) that received surgery. Results suggested that surgery reduced participant pain, but did not return motion abilities to those of controls. Further, control females had significantly greater proximal phalange motion, indicating it could be related to the onset of CMC OA. Chapter four details the creation and utilization of a novel three-dimensional analysis (termed the ‘thumb kinematic space’) of the cohorts tested in Chapter three. Quantitative and visual changes in kinematic spaces were examined. After surgery, thumb kinematic space volume was significantly reduced, did not return to those of controls, and deformity persisted. Chapter five discusses thumb metacarpal internal/external rotation, and its coupling with other joint rotations. An unexpected result was acquired, and internal/external rotation was observed before and after surgery when the CMC joint was damaged or partially removed, indicating muscle action as the primary driver of rotation. Chapter six presents the construction and use of a novel device to measure forces of the thumb in various postures independently of other fingers. Significant differences in force magnitudes suggested that standard clinical tools are insufficient. Chapter seven is an analysis of the location and direction of thumb force application, which are important factors for task completion. Control and participants with CMC OA showed similar locations and direction, which were primarily in the operative space of the thumb for daily tasks. Chapter eight is an overview of this work, its impact, and potential future expansion.
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