Single-leg squat knee biomechanics at 4 months post-operation predicts 6- and 12-month outcomes after anterior cruciate ligament reconstruction: a cohort study

Persistent functional deficits frequently complicate recovery following anterior cruciate ligament reconstruction (ACLR). This prospective cohort study investigated whether sagittal-plane knee biomechanics during a single-leg squat at 4 months post-ACLR predict functional outcomes at 6 and 12 months. Fifty-three participants underwent 3D biomechanical analysis at 4 months to measure peak knee flexion angle and moment (KFM). Clinical outcomes, including muscle strength, hop performance, and patient-reported measures, were assessed at follow-up. Regression analysis revealed that 4-month peak KFM was a consistent independent predictor of future function. Higher KFM significantly predicted greater 6-month International Knee Documentation Committee (IKDC) scores and knee extension strength, with predictive value for strength persisting at 12 months. Conversely, among the sagittal-plane variables examined, peak KFM was a stronger predictor of 6- and 12-month outcomes than peak KFA, suggesting that internal knee loading strategy during the single-leg squat (SLS) may carry greater prognostic value than squat depth. Further research is needed to determine whether biomechanical variables from other planes contribute additional predictive information.