Rupture of the anterior cruciate ligament (ACL) is a common injury during sport activities, yet the mechanism of injury is not well understood. Previous investigations have primarily examined the effects of low-magnitude or quasi-static loads, while the injury itself is a very dynamic event. Simulation models provide a potentially valuable tool to isolate the factors that influence ACL strain under dynamic conditions.
The primary aims of this study were to develop, validate and apply a dynamic three-dimensional model of the knee to investigate the influence of various loading conditions on ACL strain, to improve the understanding of ACL injury mechanisms, as well as to extend the model to unanswered ACL-related clinical research questions. These studies have revealed that the risk of ACL injury by isolated quadriceps force is significantly reduced when a sizable deceleration force is present during landing motions. These studies also suggest that the presence of a valgus moment during landing increases the ACL strain. Moreover, physiological levels of combined valgus and tibial internal rotation moments were shown to significantly increase ACL strain enough to rupture the ACL; therefore, this combined valgus and internal rotation moment is most likely the predominant ACL injury mechanism.
Another specific goal of this work was to study the influence of anatomical variation in the extensor anatomy, especially the patellar ligament insertion angle (PLIA) on quadriceps usage following ACL injury. Using gait and MRI analysis, the large net reductions in external flexion moment during walking were shown to correlate with large PLIA only in ACL deficient knees, not in uninjured contralateral knees. The existence of this relationship only in ACL-deficient knees was supported by observations of high sensitivity of anterior tibial translation to quadriceps contraction in ACL-deficient knees, using a modified version of the simulated knee model.
In conclusion, the use of a three-dimensional dynamic specimen-specific knee model provides unique insight into the factors that affect ACL strain and ACL injury mechanisms. Applications of computational studies in this thesis provide a more theoretical understanding to complement findings in other in vivo and in vitro studies.