The kinetic compensation phenomenon: Contralateral knee overload after ACL reconstruction and the modulatory effect...

Contralateral anterior cruciate ligament (ACL) injury remains one of the most frequent and devastating complications after primary reconstruction, occurring in up to 15% of athletes. Traditional return-to-sport (RTS) criteria fail to detect subtle kinetic and neuromuscular asymmetries that persist despite restoration of ligament continuity. These compensatory load-shifting mechanisms-collectively described as the Kinetic Compensation Phenomenon-may be quantifiable through a composite biomechanical index.

Two hundred sixteen competitive athletes underwent standardized single-leg hop and change-of-direction testing on dual force platforms synchronized with surface electromyography at 3, 6, and 12 months postoperatively. KCI was computed as the mean z-score of ΔVGRF, ΔLR, ΔTTS, and ΔCCI, scaled to a T-distribution (mean = 50, SD = 10). Predictive validity for contralateral ACL injury at 24 months was assessed using ROC and Cox proportional-hazard models.

The LET group demonstrated significantly lower KCI values across follow-up (p < 0.01) and a lower rate of contralateral ACL injury than the isolated BTB group (5.5% vs 12.9%; adjusted HR, 0.39; 95% CI, 0.17-0.91). KCI ≥60 predicted contralateral injury with AUC = 0.81.

LET was associated with lower contralateral kinetic overload and more symmetric biomechanical profiles during functional testing. The KCI represents a promising composite index of functional readiness that may complement conventional RTS criteria; however, external validation is required before routine clinical implementation. Composite index of functional readiness that may complement conventional RTS criteria.

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