Muscle coordination following rupture of the anterior cruciate ligament. Electromyographic studies of 14 patients.

In an electromyographic (EMG) study, the coordination in muscles acting on the knee joint was assessed in 14 patients with an arthroscopically verified complete rupture of the anterior cruciate ligament and in 16 controls. EMG and heel-contact signals were recorded while walking on a treadmill at walking gradients from 0 to 25 percent. There was an earlier onset of EMG bursts in the patients, especially in the lateral hamstrings and medial gastrocnemius; and the duration of EMG bursts also tended to be prolonged in the patients. Normalized root mean squares of amplitudes, which correlate with muscle tension, were higher in the gastrocnemius in the patients. EMG profiles, outlining the averaged muscle activity throughout the gait cycle, showed a displacement of peak activity in the hamstrings from the late swing phase into the stance phase, with increasing gradients in both the patients and the controls. Our study indicates that the gastrocnemius muscle contributes to functional stability in the anterior cruciate ligament deficient knee, and more attention should be paid to this muscle.