Increased residual anterior knee laxity at one year is associated with a dose‐dependent increase in graft re‐rupture risk following hamstring autograft ACL reconstruction in athletes

Purpose: Residual anterior knee laxity following anterior cruciate ligament reconstruction (ACLR) has been associated with inferior subjective out comes and an increased risk of revision surgery; however, its prognostic value for predicting subsequent graft re‐rupture remains unclear. This study aimed to assess the association between KT‐1000–measured 1‐year post operative anterior knee laxity and graft re‐rupture after ACLR. We hy pothesised that increased residual anterior knee laxity at 1 year post operatively would be associated with a higher risk of graft re‐rupture in a dose‐dependent manner. Methods: This retrospective cohort study included 1011 amateur and pro fessional athletes who underwent primary ACLR with hamstring tendon autograft (HTA) between 2005 and 2024 by a single surgeon using a standardised surgical technique. Patients undergoing revision ACLR, mul tiligament reconstruction, or any lateral extra‐articular augmentation pro cedure were excluded. Anterior knee laxity was quantified using the KT 1000 arthrometer at a mean of 12.1±1.3 months post‐operatively. A landmark time‐to‐event design was applied, with follow‐up starting from the KT‐1000 assessment to minimise immortal time bias and to focus on anterior knee laxity after biological graft maturation. The primary exposure was KT‐1000 side‐to‐side difference (SSD), analysed as both a continuous variable and using clinically relevant thresholds (<3mm, 3–5mm, and >5mm). Associations between post‐operative laxity and graft re‐rupture, adjusting for demographic, surgical, and activity‐related factors were assessed using a multivariable Cox proportional hazards model. Secondary analyses evaluated the relationship between KT‐1000 laxity, return‐to‐play status, and post‐operative activity level. Results: Patients who experienced graft re‐rupture had significantly greater post‐operative KT‐1000 SSD compared with those without re‐rupture (3.5 ± 1.3mm vs. 2.1±0.9mm; p<0.001). Increased KT‐1000 SSD was independently associated with higher graft re‐rupture risk (adjusted hazard ratio, 2.97 per 1‐mm increase; 95% confidence interval [CI], 2.5–3.5). Higher laxity categories were associated with progressively increased re‐rupture risk with adjusted hazard ratios of 1.76 (95% CI, 1.3–2.3; p<0.001) for 3–5mm and 8.85 (95% CI, 4.7–16.4; p<0.001) for >5mm compared with <3mm. Post‐operative 1‐year KT‐1000 anterior knee laxity was not significantly associated with return‐to‐play status (odds ratio, 0.84 per 1‐mm increase; 95% CI, 0.6–1.1; p=0.28), but was modestly associ ated with lower post‐operative Tegner activity level (p<0.001). Conclusion: KT‐1000–measured post‐operative anterior knee laxity at 1 year post‐operatively was independently associated with the risk of sub sequent graft re‐rupture after HTA ACLR in athletic patients. These findings suggest that residual laxity may serve as a useful risk stratification tool, rather than a deterministic predictor of failure, and should be interpreted in the context of overall clinical and biomechanical assessment. Level of Evidence: Level III.