Abstract
Reduced quadriceps contraction has been suggested as an adaptation to prevent anterior tibial translation in anterior cruciate ligament (ACL)‐deficient knees. This theory has been supported by a recent study that peak knee flexion moment (thought to be created by a decrease of quadriceps contraction) during walking was negatively correlated with patellar ligament insertion angle (PLIA) in ACL‐deficient knees, but not in contralateral, uninjured knees. In addition, the PLIA was significantly smaller in ACL‐deficient knees than in contralateral, uninjured knees. However, it is unknown whether ACL reconstruction restores the PLIA or whether the relationship between the PLIA and knee flexion moments previously observed in ACL‐deficient knees disappears. This study tested the following hypotheses: (1) The PLIA of ACL‐reconstructed knees is significantly smaller than the PLIA of uninjured contralateral knees; (2) Peak knee flexion moment (balanced by net quadriceps moment) during walking is negatively correlated with the PLIA in ACL‐reconstructed knees. The PLIA of 24 ACL‐reconstructed and contralateral knees were measured using MRI, and peak knee flexion moments during walking were measured. Results showed that the PLIA of ACL‐reconstructed (22.9 ± 4.4°) knees was not significantly smaller (p = 0.09, power = 0.99) than the PLIA of contralateral (24.1 ± 4.8°) knees. Peak knee flexion moment was not correlated with the PLIA following ACL reconstruction (R^2^ = 0.016, power = 0.99). However, the magnitude of the knee flexion moment remained significantly lower in ACL‐reconstructed knees. In summary, this study has shown that the PLIA of ACL‐reconstructed knees returned to normal and that patients no longer adapt their gait in response to the PLIA, though quadriceps function did not return to normal levels. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27: 730–735, 2009