Anterior cruciate ligament reconstruction (ACLR) is often performed to reproduce the function of the original ligament and restore functional stability of the knee joint following ACL injury. Despite substantial improvements in surgical techniques and satisfactory outcomes, individuals who have undergone ACLR have been shown to have a higher risk of developing osteoarthritis (OA) at the knee. To date, the underlying mechanism(s) for the high risk of knee OA in individuals post-ACLR are not fully understood. The primary objectives of this dissertation were to develop a subject-specific EMG-driven model to examine whether females with ACLR demonstrate greater tibiofemoral compressive forces when compared to healthy females, and to examine whether muscle co-contraction and tibiofemoral compressive forces in females who have undergone ACLR can be reduced when trained to utilize a landing strategy that emphasizes greater hip and knee flexion. Chapter III describes the development of an imaging-based subject-specific EMG-driven knee model to quantify the joint forces at the tibiofemoral joint. Using this model, the purpose of Chapter IV was to determine whether females who have undergone ACLR demonstrate greater tibiofemoral compression when compared to healthy females. Results revealed that females who have undergone ACLR exhibit greater peak tibiofemoral compressive forces when compared to healthy controls. The increased tibiofemoral compressive force observed in ACLR subjects was accompanied by increased muscle co-contraction and decreased knee flexion during landing. The purpose of Chapter V was to examine whether utilization of a landing strategy that emphasizes greater hip and knee flexion can decrease tibiofemoral compressive forces in the ACLR population.
Consistent with the proposed hypotheses, a decrease in peak tibiofemoral compressive forces was observed when female individuals post-ACLR were trained to land with greater hip and knee flexion. The decreased tibiofemoral compressive force was accompanied by decreased muscle co-contraction at the knee. Overall, the findings of this dissertation support the premise that individuals with ACLR exhibit elevated tibiofemoral compressive force, which may contribute to the high risk of knee OA in this population. The findings of this dissertation also indicate that muscle co-contraction as well as elevated tibiofemoral compressive forces observed in individuals who have undergone ACLR can be reduced by utilizing a landing strategy that encourages greater hip and knee flexion. Interventions aimed at correcting abnormal neuromuscular strategies following ACLR should be emphasized in an effort to minimize the loading at the tibiofemoral joint.