The kinetic compensation phenomenon: Contralateral knee overload after ACL reconstruction and the modulatory effect of lateral extra-articular tenodesis.

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSION

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.

LEVEL OF EVIDENCE: II.