The role played by anatomic factors in ACL injury remains elusive. In this study, objective methods were used to characterize ACL volume, tibial slopes, and notch geometry from ACL-injured and matched control subjects. The study tested four hypotheses: 1) the medial tibial plateau slope is steeper posteriorly in the injured group compared to the non-injured group, 2) the lateral tibial plateau slope is steeper posteriorly in the injured group compared to the non-injured group, 3) the femoral intercondylar notch dimensions are smaller in the injured group compared to the non-injured group and 4) the ACL volume, tibial plateau slopes and intercondylar notch dimensions are all independent of each other. Fifty-four subjects were divided into two groups, those who had suffered a non-contact ACL injury and those who still had two healthy ACLs, matched to the injured subjects by gender, age, height and weight. The lateral tibial plateaus in the uninjured contralateral knees of the injured subjects had a significantly steeper posterior slope (1.8° vs. −0.3°), a factor that potentially contributed to the ACL injury in the opposite knee. The intercondylar notch dimensions were found to be smaller in the injured subjects, potentially putting the ACL at risk of impingement, and intercondylar notch volume was correlated to ACL volume (r=0.58). Discriminant analysis showed that the notch width at the inlet was the best single predictor of ACL injury.

The presence and thickness of an anteromedial bone ridge in the femoral notch has been identified as a potential risk factor for noncontact anterior cruciate ligament injury. A biomechanical injury model involving the femoral notch ridge in anterior cruciate ligament tears is proposed in which the anterior cruciate ligament may be tented and stretched over the anteromedial notch ridge during knee valgus and internal tibial rotation; alternatively, the anterior cruciate ligament may be impinged at the lateral anterior outlet wall during knee valgus and external tibial rotation. Further investigation to determine the origin of the bone ridges and the validity of the proposed injury model is recommended.

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