Hamstring weakness as an indicator of poor knee function in ACL-deficient patients

Anterior cruciate ligament (ACL) rupture causes instability to the knee joint which leads each patient to a different degree of disability. The purpose of this study was to examine the strength of the quadriceps and the hamstrings in ACL-deficient amateur soccer players at different levels of functional status. Thirty male amateur soccer players were separated into three groups according to their Lysholm score; the high-L1 (Lysholm ≥84), the intermediate-L2 (84> Lysholm ≥72) and the low-L3 (Lysholm <72) knee function groups. The control group consisted of 12 amateur soccer players. The strength of the quadriceps and hamstrings was assessed isokinetically at 60°/s. The quadriceps demonstrated significant deficits of the injured knee compared to the intact knee in all groups, whilst the hamstrings showed significant weakness only in the low function group. Respective percentage deficits in groups L1, L2 and L3 were 13.7%, 16.0% and 18.6% for the quadriceps and 2.4%, 5.6% and 19.2% for the hamstrings. All groups had significant quadriceps weakness which did not differ between the groups. In contrast, the strength deficit of the hamstrings was an indicator of poor knee function, since they were significantly weak only in group L3, which represented patients who clearly failed to compensate for instability symptoms. In groups L1 and L2 the side-to-side differences were within the area of asymmetry measured in the control group. Clinical importance of the results is discussed.