Activity Level and Graft Type as Risk Factors for Anterior Cruciate Ligament Graft Failure A Case-Control Study

Background: Anterior cruciate ligament (ACL) graft failure is an uncommon but devastating event after reconstruction, and risk factors for graft failure are not well understood. Hypothesis: Returning to a high activity level after ACL reconstruction and use of an allograft are risk factors for ACL graft failure. Study Design: Case-control study; Level of evidence, 3. Methods: Twenty-one patients with ACL graft failure were identified over a 2-year period. Forty-two age- and sex-matched controls were identified over the same period. A 1: 2 matched case-control design was used to evaluate activity level after reconstruction and graft type as risk factors for ACL graft failure. Logistic regression analysis was used to determine odds ratios for activity level after reconstruction and for graft type among cases and controls. Association (interaction) between activity level after reconstruction and graft type was evaluated comparing stratum-specific odds ratios. Results: Univariate logistic regression models showed an increased odds of ACL graft failure for those with high activity level compared with low activity level (odds ratio [OR], 5.53; 95% confidence interval [CI], 1.18-28.61; P = .03) and for allografts compared with autografts (OR, 5.56; 95% CI 1.55-19.98; P = .009). A bivariate logistic regression model showed a 35% change in the odds ratio for activity level (OR, 4.33; 95% CI, 0.89-21.16; P = .07) and a 13% change in the odds ratio for allograft compared with autograft (OR, 4.93; 95% CI, 1.34-18.20; P = .02). Stratum-specific odds ratios between activity level and graft type show a multiplicative interaction between higher activity level and allograft for much greater odds of ACL graft failure. Conclusion: Higher activity level after reconstruction and allograft use for reconstruction are risk factors for ACL graft failure. Stratum-specific odds ratios show a multiplicative interaction between higher activity level after ACL reconstruction and allograft use, greatly increasing the odds for ACL graft failure.