Serial Changes in Knee Muscle Strength After Anterior Cruciate Ligament Reconstruction Using Hamstring Tendon Autografts

Purpose: The purpose of this study was to evaluate serial changes in quadriceps and hamstring muscle strength over the first postoperative year in patients who underwent anterior cruciate ligament (ACL) reconstruction with an autologous hamstring tendon graft and to reveal which of these 2 muscles lost more strength and recovered more slowly after autologous hamstring ACL reconstruction. Methods: Isokinetic muscle strength was measured preoperatively and at 6 months and 1 year postoperatively in 20 patients who underwent ACL reconstruction. The maximal torque (60 degrees/s) and total work (180 degrees/s) of the quadriceps and hamstring were evaluated using an isokinetic testing device. The isokinetic muscle strength and endurance of the injured legs were expressed as percentages of those of the uninjured legs at the same time point. Results: Both quadriceps and hamstring muscle strength at 60 degrees/s and endurance at 180 degrees/s of the injured relative to the uninjured leg was 50% preoperatively. Quadriceps muscle strength and endurance of the injured leg increased to 70% at 6 months and 80% at 1 year postoperatively, whereas hamstring muscle strength and endurance increased to 80% at 6 months and 80% at 1 year. Conclusions: Knee muscle strength recovered progressively after ACL reconstruction using autologous hamstring tendons but did not fully recover, being about 80% that of the uninjured leg even 1 year after surgery.