The ankle is one of the most common sites for acute musculoskeletal injuries, and sprains account for 75% of ankle injuries. Acute ankle trauma is responsible for 10 to 30% of sports-related injuries in young athletes. Each year, an estimated one million persons present to physicians with acute ankle injuries. More than 40% of ankle sprains have the potential to cause chronic problems. While lateral ankle sprains are the most common injury, high ankle sprains represent a more disabling problem and require a longer recovery period and different treatment. Injury to the tibiofibular syndesmosis ligaments, which bind together the distal ends of the tibia and fibula, is commonly referred to as a high ankle sprain. External rotation of the foot has been implicated in high ankle sprains, but the mechanism of injury is still unclear and the pathologies due to external foot rotation remain controversial. The mechanisms of lateral ankle sprains are better understood to evolve from foot inversion, but the level of strain being produced in lateral ligaments during such injuries is yet unclear.The mechanisms of sports-related injuries can be studied with various approaches: cadaver experiments, kinematic studies and computational modeling. The advantage of human cadaver tests is that the forces and motions experienced by the ankle joint can be controlled and measured with great precision. Dissections of joints after testing can also allow for an in-depth study of ligament and bone injuries. While ligament damages due to excessive strains are often involved in most sports-related injuries, studies with cadaver ankles may not reflect ligament behaviors during injury-producing events in living humans. Three-dimensional simulations of human movements using dynamic, computational models can offer an attractive method to separate various motions of the ankle bones, rapidly solve for motion-based mechanics, and determine ligament strains during physiological motions.In this dissertation, cadaver studies were conducted to investigate ankle responses to external foot rotation with different foot and shoe constraints. A computational ankle model has also been developed and validated against cadaver experiments and studies with human subjects. These studies showed that external rotation of a highly everted foot generated a high ankle sprain (ligamentous damage to the anterior tibiofibular ligament), while external rotation of a neutral foot produced a ligamentous injury to the antero-medial aspect of the ankle (damage to the anterior deltoid ligament). In addition to the failure level testing, a low level testing with football shoes showed that while flexible shoes generated lower joint torques than rigid shoes during external foot rotation, they produced more talus eversion that may induce strain in the anterior tibiofibular ligament. Ligamentous injuries due to excessive foot inversion have also been studied using the computational model in this dissertation. These studies provide a better understanding to the mechanisms of various ankle injuries that might aid in prevention programs and treatment strategies for these trauma patients.
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