Abstract
Theoretical compensation after anterior cruciate ligament (ACL) tear could cause quadriceps weakness and hamstring activation, preventing anterior tibial subluxation and affecting the expected hamstring-to-quadriceps ratio. Although quadriceps weakness often occurs after ACL tears, it remains unclear whether hamstring strength and hamstring-to-quadriceps ratio increase in ACL deficient knees. This meta-analysis compared the isokinetic muscle strength of quadriceps and hamstring muscles, and the hamstring-to-quadriceps ratio, of the injured and injured limbs of patients with ACL tears. This meta-analysis included all studies comparing isokinetic thigh muscle strengths and hamstring-to-quadriceps ratio in the injured and uninjured legs of patients with ACL tear, without or before surgery. Thirteen studies were included in the meta-analysis. Quadriceps and hamstring strengths were 22.3 N∙m (95% CI: 15.2 to 29.3 N∙m; P<0.001) and 7.4 N∙m (95% CI: 4.3 to 10.5 N∙m; P<0.001) lower, respectively, on the injured than on the uninjured side. The mean hamstring-to-quadriceps ratio was 4% greater in ACL deficient than in uninjured limbs (95% CI: 1.7% to 6.3%; P<0.001). Conclusively, Decreases were observed in both the quadriceps and hamstring muscles of patients with ACL tear, with the decrease in quadriceps strength being 3-fold greater. These uneven reductions slightly increase the hamstring-to-quadriceps ratio in ACL deficient knees.
Highlights
Following injury to the anterior cruciate ligament (ACL), isokinetic quadriceps strength is generally lower in the injured than in the contralateral uninjured knee due to arthrogenic muscle inhibition.[1,2,3] This phenomenon is considered a natural compensating mechanism to prevent anterior subluxation that may result in painful and potentially detrimental movements of the injured knee.[4]
Sec and one each at 30°/sec, 90°/sec, 120°/sec and 270°/sec, showed that isokinetic hamstring strength was 4.9 NÁm lower in the injured than the uninjured limb. These findings demonstrated that, like quadriceps strength, hamstring strength was lower in legs with than without ACL tears
Quadriceps strength was shown to be altered in patients with ACL tears, a type of compensatory mechanism to reduce the anterior tibial subluxation caused by a torn ACL
Summary
Following injury to the anterior cruciate ligament (ACL), isokinetic quadriceps strength is generally lower in the injured than in the contralateral uninjured knee due to arthrogenic muscle inhibition.[1,2,3] This phenomenon is considered a natural compensating mechanism to prevent anterior subluxation that may result in painful and potentially detrimental movements of the injured knee.[4] This compensating mechanism may include the facilitation or activation.
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