Increased posterior tibial slope is a risk factor for anterior cruciate ligament injury and graft failure after reconstruction: A systematic review

IMPORTANCE: Anterior cruciate ligament (ACL) injury and ACL reconstruction (ACLR) graft failure are important clinical concerns that result in long recovery periods, potential long-term knee instability, and poor patient outcomes. Identifying risk factors such as posterior tibial slope (PTS), meniscal slope (MS), and meniscal bone angle (MBA) is important for improving risk stratification, guiding management decisions, and reducing the incidence of both ACL injury and ACLR graft failure. OBJECTIVE: This systematic review and meta-analysis aim to determine whether increased PTS, increased MS, and decreased MBA serve as independent predictors of both ACL injury and ACLR graft failure. EVIDENCE REVIEW: A comprehensive search of the literature was conducted following Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines. For evaluating ACL injury, the review included comparative studies measuring PTS, MS, or MBA between ACL injury patients and ACL-intact controls. For ACLR graft failure, studies comparing these measurements between patients with ACLR graft failures and those with successful ACLR outcomes were included. Data were pooled using a random-effects model to calculate the overall mean difference (MD) between groups. FINDINGS: Out of 1,683 initially identified studies, 75 studies were selected for detailed analysis, 53 analyzing ACL injury and 24 studies analyzing ACLR graft failure. The meta-analysis revealed that increased PTS significantly increases the risk of both ACL injury (MD 1.64°; 95% CI: 1.08-2.20, p ​< ​0.01) and ACLR graft failure (MD 1.76°; 95% CI: 1.03-2.48, p ​< ​0.01). This is statistically significant for both lateral and medial PTS, and across both radiograph and magnetic resonance imaging. A higher lateral MS (MD 3.25°; 95% CI: 1.70-4.80, p ​< ​0.01) and a lower lateral MBA (MD -3.85°; 95% CI: -6.38-1.32, p ​< ​0.01) were also significantly associated with an increased risk of ACL injury. However, no statistically significant differences were observed for MS or MBA between ACLR graft failure and successful ACLR groups. CONCLUSION AND RELEVANCE: The findings indicate that increased PTS, whether measured medially or laterally, is a statistically significant risk factor for both ACL injury and ACLR graft failure. Additionally, increased lateral MS and decreased lateral MBA are associated with ACL injury. This evidence supports the consideration of tibial slope in risk assessment, preoperative planning, and surgical decision-making for both prevention of ACL injury and ACLR procedures. Further research is necessary to fully understand the role of MS and MBA in ACL injury. LEVEL OF EVIDENCE: Level IV; systematic review of level III-IV studies.