Weakness of thigh muscles in individuals sustaining anterior cruciate ligament injury.

The purpose of this study was to assess the quadriceps and hamstrings muscle strength deficits at different knee flexion angles (30 degrees and 60 degrees) in individuals who had sustained anterior cruciate ligament (ACL) injury, who had never had thigh muscle strengthening exercise. Isometric (0 degree/sec) and isokinetic (60 degrees/sec and 180 degrees/sec) torque measurements were performed on sixty-six patients (29 males and 37 females) with chronic ACL insufficiency. Significant strength deficits of the quadriceps and hamstrings muscles in injured knees were found at both 30 degrees and 60 degrees of knee flexion in three testing conditions (0 degree/sec, 60 degrees/sec, and 180 degrees/sec). In the comparison of torque production at 30 degrees and 60 degrees knee flexion angles, for the male group, significantly greater deficits of the quadriceps torque were found at 60 degrees knee flexion than at 30 degrees knee flexion in the isometric and isokinetic 60 degrees/sec testing modes. For the female group, significantly greater deficit of the quadriceps torque was found at 60 degrees knee flexion than at 30 degrees knee flexion only in isokinetic 60 degrees/sec. There was no significant difference of the hamstrings torque deficit between 30 degrees and 60 degrees knee flexion in any testing modes. In the comparison of isometric and two isokinetic testing modes (60 degrees/sec and 180 degrees/sec), for the male group, significantly greater deficits of the quadriceps torque were found at 30 degrees knee flexion in isokinetic 180 degrees/sec and at 60 degrees knee flexion in isokinetic 60 degrees/sec as compared to the isometric test. There was no statistical difference in the hamstrings torque values. For the female group, significantly greater deficits of the quadriceps and hamstrings torque were found at 30 degrees knee flexion in isokinetic 60 degrees/sec and at 60 degrees in isokinetic 60 degrees/sec and 180 degrees/sec as compared to the isometric test. It was concluded that long lasting instability without any muscle exercises may result in the weakness of not only the quadriceps muscle but also even hamstrings muscle, and that the quadriceps strength might be more susceptible to ACL insufficiency at 60 degrees knee flexion angle than at 30 degrees knee flexion angle, whereas, the hamstrings did not show any angular-specific torque deficits. These findings might resulted from characteristics of torque-curves of the quadriceps and hamstrings muscles.(ABSTRACT TRUNCATED AT 400 WORDS)