Squatting Mechanics in People With and Without Anterior Cruciate Ligament Reconstruction

Abstract

Background: Single-legged squat mechanics change after anterior cruciate ligament (ACL) reconstruction and rehabilitation, but it is unclear if changes in squat mechanics are graft specific. Purpose: To investigate graft differences in biomechanics of the knee, hip, and trunk during the single-legged squat in patients with ACL-reconstructed knees, determine if these factors were associated with deficits in knee extension moment, and determine if subjective knee function and squat biomechanics are related. Study Design: Cross-sectional study; Level of evidence, 3. Methods: A total of 106 individuals were grouped based on surgical status and graft type (51 control, 34 bone–patellar tendon–bone [BPTB], 21 ipsilateral semitendinosus and gracilis autograft [ISGA]). Motion capture interfaced with force plates was used to capture single-legged squat performance in the ACL reconstructed and dominant control limbs. Variables were captured at peak knee flexion. Results: Controls exhibited greater knee extension moment ( P = .04), knee flexion ( P = .002), and hip adduction angles ( P = .04) compared with the reconstructed groups. The ISGA group demonstrated greater forward ( P = .01) and lateral ( P = .002) trunk flexion over the reconstructed limb. Summated extension moment did not differ between groups ( P = .42). Knee extension moment was correlated with lateral trunk flexion ( r = −0.31, P = .03) in the control group and knee flexion angle ( r = −0.44, P = .04) in the ISGA group. Subjective knee function scores were correlated with lateral trunk flexion ( r = −0.45, P = .008) in the BPTB group and with hip adduction angle ( r = −0.46, P = .04) and hip extension moment ( r = 0.48, P = .03) in the ISGA group. Conclusion: Knee and hip biomechanics were related to surgical status but not graft type. Increased forward and lateral trunk motion in the ISGA group may be a mechanism to protect the knee by minimizing motion during squatting or related to surgical selection bias. Secondary findings (summated extensor moments and correlations) most likely represent a strategy to shift the squat demands from the knee to the hip. Clinical Relevance: Clinicians should target these neuromuscular deficits during rehabilitation and training programs after ACL reconstruction.