Relationship between quadriceps femoris muscle volume and muscle torque after anterior cruciate ligament repair

This study was performed to obtain evidence regarding bilateral hindrance of motor unit (MU) recruitment in the quadriceps femoris (QF) of patients with anterior cruciate ligament (ACL) reconstruction. The subjects included 70 patients who underwent ACL reconstruction and 35 healthy subjects. To identify the muscle torque per unit volume (MTPUV), the peak torque of each velocity of isokinetic performance was divided by muscle volume of the QF measured by a series of cross-sectional images obtained by magnetic resonance imaging scans. Tests revealed that the mean MTPUV of the uninjured (0.113±0.03 N m/cm³ at 60°/s, 0.081±0.02 N m/cm³ at 180°/s) and injured sides (0.109±0.03 N m/cm³ at 60°/s, 0.079±0.023 N m/cm³ at 180°/s) were significantly lower than those of the control group (0.144±0.05 N m/cm³ at 60°/s, 0.096±0.04 N m/cm³ at 180°/s). Previous studies suggested that MU recruitment in the QF of patients with ACL injury was hindered bilaterally. However, the design of their studies could not provide evidence of bilateral hindrance of MU recruitment in the QF. The results of the present study demonstrated that the MTPUV of both injured and uninjured sides of patients were significantly lower than those of the control group.