ACL injury mechanisms

Abstract

Model-based image-matching (MBIM) technique has enabled detailed video analysis of injury situations that had been limited to simple visual inspection. We have analyzed anterior cruciate ligament (ACL) injury situations from ten analogs and one HD video sequence using the MBIM technique. The knee kinematical patterns were remarkably consistent, with immediate valgus and internal rotation (IR) motion occurring within 40 ms after initial contact (IC), and then an external rotation was observed. Peak vertical ground reaction force (GRF) occurred at 40 ms after IC. Based on these results, it is likely that the ACL injury occurred approximately 40 ms after IC. 9 mm of abrupt anterior tibial translation at the time of injury was also detected in the HD video. On the other hand, the hip kinematics was constant at abducted, flexed, and IR position during 40 ms after IC. Based on these results together with previous studies, we proposed a new hypothesis for ACL injury mechanisms that valgus loading and lateral compression generate IR motion and anterior translation of tibia, due to the joint geometry, resulting in ACL rupture. Moreover, it seems that the hip is relatively "locked" at IC and cannot absorb energy from GRF and knee is exposed to a larger force, which leads to ACL injury. These results suggest that prevention programs should focus on acquiring a good cutting and landing technique with knee flexion avoiding knee valgus and foot internal rotation and with hip flexion to absorb energy from GRF. Moreover, the fact that the ACL injury occurs 40 ms after IC suggests that "feed-forward" strategies before landing may be critical, as "feedback" strategies are too slow to prevent ACL injuries.