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The influence of tibial slope on anterior cruciate ligament graft failure risk is dependent on graft positioning

Background: Increased lateral tibial posterior slope (LTPS) is associated with higher anterior cruciate ligament (ACL) reconstruction (ACLR) failure rate. Transportal central femoral footprint ACLR is associated with higher failure rate compared to transtibial high anteromedial footprint ACLR due to graft anisometry. The purpose of this study was to investigate whether the influence of tibial slope on ACL graft failure risk is dependent on graft positioning. Material: Of the 1480 consecutive hamstring ACLRs, 30 transportal (central femoral tunnel placement) and 30 transtibial (high anteromedial tunnel placement) ACLR failures were evaluated and matched one-to-one with non-failure control participants by age, sex, graft and surgical technique. Lateral tibial slope was assessed on MRI. Results: The risk of graft failure in the transportal group increased by 40.5% per degree of increasing LTPS (odds ratio 1.4; 95% confidence interval 1.05–1.87; p = 0.02). The transportal failure group showed a significantly higher mean tibial slope of 8.6° compared to both the transportal control group with 7.1° (p = 0.03) and the transtibial failure group with 7.2° (p = 0.04). Increased tibial slope was associated with shorter time to reconstruction failure (p = 0.002). The difference between slopes in the transtibial failure group (7.2°) compared to the transtibial control group (7.1°) was not significant (p = 0.56). Conclusion: Increased LTPS is associated with significantly increased risk of graft failure only in transportal ACLR, not in transtibial ACLR. Slope-related graft strain may be potentiated by anisometric ACL graft placement.