Association of Preoperative Asymmetry in Vertical Ground-Reaction Force With Knee Extensor Symmetry 1 Year After Anterior Cruciate Ligament Reconstruction

Background: Preoperative and postoperative asymmetries in knee kinematics and kinetics, particularly in vertical ground-reaction force (vGRF), have been linked to long-term functional outcomes after anterior cruciate ligament (ACL) reconstruction. Gait asymmetry may indicate altered neuromuscular control and compensatory cocontraction strategies, which can compromise joint integrity and delay recovery. Purpose: To determine whether preoperative vGRF asymmetry could predict postoperative knee extensor strength symmetry and neuromuscular recovery 1 year after ACL reconstruction. Study Design: Cohort study; Level of evidence, 2 Methods: A total of 55 patients undergoing ACL reconstruction were prospectively evaluated before surgery and at 1 year postoperatively. Assessments included vGRF, gait speed, surface electromyography, isokinetic knee extensor/flexor strength, and the Knee injury and Osteoarthritis Outcome Score (KOOS) questionnaire. Based on preoperative vGRF data, participants were categorized into lesser-loading and greater-loading groups. Three-dimensional motion capture and synchronized force plates were used to analyze gait and cocontraction indices. Generalized estimating equations were applied to evaluate group × time effects, with statistical significance set at P < .05. Results: Both groups demonstrated pain reduction and improved KOOS scores postoperatively, accompanied by partial restoration of vGRF symmetry. The greater-loading group (n = 28) exhibited significant improvement in knee extensor strength symmetry (from 66% to 87%; P = .001), whereas the lesser-loading group (n = 27) showed persistent muscle cocontraction (0.12-0.12; P = .94) and less improvement in knee extensor strength symmetry (from 67% to 75%; P = .11). These results indicate distinct neuromuscular adaptation patterns depending on preoperative loading asymmetry. Conclusion: Our study showed that preoperative vGRF asymmetry is a clinically feasible indicator of neuromuscular recovery potential after ACL reconstruction. Patients with reduced injured-limb loading showed persistent cocontraction and weaker quadriceps strength, underscoring the value of early gait assessment for targeted rehabilitation.