Compensatory muscle activity in the posterior cruciate ligament-deficient knee during isokinetic knee motion.

We performed electromyographic analyses in 12 patients with posterior cruciate ligament-deficient knees to compare electrical activity in the quadriceps, hamstring, and gastrocnemius muscles between the uninjured and involved limbs. Each patient performed concentric isokinetic knee motion at 30 and 60 deg/sec in both limbs separately. Torques in knee extension and flexion and surface electromyograms from the quadriceps, medial hamstring, and medial gastrocnemius muscles were simultaneously recorded. The uninjured limb served as a control for each patient. Before generation of flexion torque, the gastrocnemius muscle was electrically activated significantly earlier in posterior cruciate ligament-deficient knees than in uninjured knees at each velocity. However, we could not find any significant differences between the posterior cruciate ligament-deficient and uninjured knees in torque curves and electromyelograms of the quadriceps and hamstring muscles. This study suggests that early contraction of the gastrocnemius muscle may be a part of a compensatory mechanism in posterior cruciate ligament-deficient knees.