Acute ankle damage is one of the most commonly observed athletic injuries, accounting for 10-30% of sports-related injuries in young athletes. Most frequently, damage occurs to the lateral ligamentous complex, involving the anterior talofibular ligament and calcaneofibular ligament. Medial ankle injuries involve damage to the anterior deltoid ligament, while syndesmotic (or high) ankle injuries are defined as damage to the anterior tibiofibular ligament. While less common than lateral ankle injuries, both medial and high ankle injuries are of particular interest to researchers due to their longer recovery time and potential for long-term ankle dysfunction. While combinations of eversion, dorsiflexion, and external rotation are often implicated in medial and high ankle sprains, the exact mechanisms are still unclear. Additionally, although studies have investigated the effect of shoe-surface interface on injury risk, few researchers have examined the effect of shoe rotational stiffness on motion of the ankle, torque generated, and subsequent injury location and severity during external rotation. One hypothesis of this dissertation was that the motion of the ankle joint and the location of injury during external rotation are functions of both the position of the ankle prior to rotation and the amount of constraint on the ankle. A second hypothesis was that specimen-specific, rigid body modeling could be utilized to simulate injury-level ankle rotation in addition to modeling the effect of different footwear on motion of the ankle. Computational modeling, in addition to cadaveric and in vivo human subject testing was utilized to test these hypotheses. Specimen-specific computational models simulating injuries observed experimentally revealed that external foot rotation primarily strains the medial ankle ligaments, but pre-everting the ankles prior to rotation puts the primary strain on the syndesmotic ankle ligaments. Additionally, there was a significant difference in the amount of strain in simulations modelling complete ruptures versus partial tears. A follow-up study involving the measurement of cadaver joint kinematics during external foot rotation concluded there was significantly more talocrural joint rotation, but significantly less subtalar joint rotation in a neutral versus pre-everted ankle, potentially explaining the location of injury during external rotation. In a separate cadaver study investigating the effect of foot constraint, ankles constrained by a `stiff' football shoe experienced more ankle joint rotation, but less eversion than ankles constrained by a more `flexible' shoe. As a result, ankles in stiff shoes experienced combination syndesmotic and medial ankle injuries in addition to high strains in these ligaments. Ankles in flexible shoes saw less combination injuries, but higher strains in the subtalar ligaments. This effect of ankle constraint on joint motion was then quantified by measuring joint kinematics in human subjects, and computational modelling provided an estimation of injury risk as a function of foot rotation and constraint. A final human subject study involved calculating the stiffness of the unconstrained ankle joint during voluntary external foot rotation in order to more accurately model the ankle in the future. The information from these studies may aid in the implementation of preventative measures in order to mitigate the risk of future ankle injury resulting from excessive levels of external rotation.
Read
