The anterior cruciate ligament enigma. Injury mechanisms and prevention.

The reasons for the higher frequency of anterior cruciate ligament injuries in women are largely conjecture. These injuries may result from direct contact or, more frequently, from no direct contact to the knee during activities that most athletes consider routine to their sport. This implies that there are intrinsic factors that lead to anterior cruciate ligament rupture. For the anterior cruciate ligament to tear, there must be excess anterior tibial translation or rotation of the femur on the tibia. In the former case, the tibia can move anteriorly during quadriceps activation that is not counterbalanced by hamstring activation. Patients describe their injury as occurring when landing, stopping, or when planting to change directions. The knee typically was near full extension. Mechanically, the angle of the patellar tendon and tibial shaft increases as the knee approaches full extension. This gives a mechanical advantage to the quadriceps. During cutting maneuvers, athletes tend to cut with a knee near extension (0 degree-20 degrees) when the quadriceps are active and the hamstrings are neither very active nor at a knee flexion angle that offers much of a mechanical advantage. In performing cutting and landing maneuvers, women tend to perform the activities more erect; that is, with their knee and hips closer to extension. One possible factor to help reduce the frequency of anterior cruciate ligament injuries in women may be in proper instruction for performing cutting and landing maneuvers which will lower their center of gravity thereby denying the quadriceps the opportunity to shift the tibia anteriorly.