A risk-factor model for anterior cruciate ligament injury.

The incidence of non-contact anterior cruciate ligament (ACL) injury is reported to be 6-8 times greater in females than males competing in the same activities. Injury to the ACL occurs as a result of insufficient stability of the tibiofemoral joint, which fails to prevent posterior dislocation of the femur on the tibia. The stability of the tibiofemoral joint is maintained by passive (non-contractile) and dynamic (contractile) mechanisms. The passive mechanisms include the shape of the articular surfaces, the menisci, the ligaments and the joint capsule. The dynamic mechanisms consist of the muscle-tendon units that cross the joint, in particular, the quadriceps and hamstrings. The relative significance of the various passive and dynamic mechanisms in maintaining the stability of the tibiofemoral joint is not clear. A number of intrinsic and extrinsic risk factors have been proposed to account for the sex difference in the incidence of ACL injuries. However, most of the proposed risk factors have arisen from univariate correlation studies based on relatively small samples.