The lower-extremity musculature in chronic symptomatic instability of the anterior cruciate ligament.

We studied the musculature of the lower extremity in forty-one patients with chronic symptomatic instability of the anterior cruciate ligament. Computed tomographic and clinical measurements of the limb were taken at levels fifteen and twenty-five centimeters proximal to the medial joint line and ten centimeters distal to it. Biopsy specimens from the vastus lateralis of both lower extremities were analyzed by histochemistry and electron microscopy. Computed tomography revealed a decrease in the muscle square area of the affected thigh of 8 per cent as compared with the control lower extremity. There was quadriceps atrophy of 10 per cent and hamstrings atrophy of only 4 per cent. The atrophy of the vastus medialis was significantly greater than that of the entire quadriceps. Histochemistry revealed a similar decrease in fiber size for all fiber types, and hence no shift in fiber type. Electron microscopy showed an increase in intracellular fat but no change in mitochondrial volume density or capillarization.