Comparison of closed and open kinetic chain exercise in the anterior cruciate ligament-deficient knee.

The purpose of this study was to quantify the amount of anterior tibial displacement occurring in anterior cruciate ligament-deficient knees during two types of rehabilitation exercises: 1) resisted knee extension, an open kinetic chain exercise; and 2) the parallel squat, a closed kinetic chain exercise. An electrogoniometer system was applied to the anterior cruciate ligament-deficient knee of 11 volunteers and to the uninvolved normal knee in 9 of these volunteers. Anterior tibial displacement and the knee flexion angle were measured during each exercise using matched quadriceps loads and during the Lachman test. The anterior cruciate ligament-deficient knee had significantly greater anterior tibial displacement during extension from 64 degrees to 10 degrees in the knee extension exercise as compared to the parallel squat exercise. In addition, the amount of displacement during the Lachman test was significantly less than in the knee extension exercise, but significantly more than in the parallel squat exercise. No significant differences were found between measurements in the normal knee. We concluded that the stress to the anterior cruciate ligament, as indicated by anterior tibial displacement, is minimized by using the parallel squat, a closed kinetic chain exercise, when compared to the relative anterior tibial displacement during knee extension exercise.