Eccentric contraction strength of knee extensor before and after anterior cruciate ligament reconstruction

Twelve men and eighteen women with a mean age of 22 (15-32) years who underwent anterior cruciate ligament (ACL) reconstruction using semitendinosus muscle tendon were studied. The quadriceps strength was isokinetically measured during concentric and eccentric contractions. When the muscle strength was examined before ACL reconstruction, the injured/uninjured ratio was 72.9% for eccentric contraction, which was significantly lower than the 81.4% for concentric contraction. For postoperative muscle, the injured/uninjured ratio was 98.6% for eccentric contraction and 80.6% for concentric contraction, showing better recovery of muscle strength for eccentric contraction. The observation of lower muscle strength for eccentric contraction than for concentric contraction in knees before ACL reconstruction may be explained by the fact that movements such as stop and turn become difficult due to ACL dysfunction. The result is that the patient avoids exerting eccentric knee extension and contraction forces even in daily living activities. On the other hand, once the joint instability is improved by ACL reconstruction, patients do not need to avoid movements such as stop and climbing down stairs that require eccentric contraction strength. This may account for good recovery of the muscle strength for eccentric contraction.