Proposed Mechanism for Non-Contact Anterior Cruciate Ligament Injury

This case report illustratesa theory of a mechanism of injury for anterior cruciate ligament (ACL) tears. Studies show ACL injuries can occur with maximal quadriceps muscle contraction. When the timing of the foot plant is miscalculated and is a split second later than planned, the exaggerated muscle contractions cause the tibia to shift more anterior than what would have occurred had the foot struck the ground at the correct time. With anterior translation, the tibia becomes internally rotated because the shorter and downward slope of the lateral tibialplateau, and this puts the ACL in an lengthened position. At the time of foot plant and impact, the sulcus terminalis of the lateral femoral condyle contacts the posterolateral tibial plateau. I propose that the impact of the femur on the posterior part of the tibia causes a fulcrum action, pushing it further anteriorly and medially, causing the lengthened ACL to rupture. Bone bruises on the lateral aspect of the femoral condyle and the posterolateral aspect of the tibial plateau, which occur at the time of impact, can be explained by this mechanism. The fulcrum action of the femur pushing the tibia forward causing an ACL injury has not been described. Case Report