Introducing “Delta Angle” of Posterior Tibial Slope and Its Impact on ACL Reconstruction Failures: A Regression Analysis of 1174 Patients

Anterior cruciate ligament reconstruction (ACLR) failures are linked to various risk factors, including an increased posterior tibial slope (PTS). Recent studies have indicated that both the medial PTS (MPTS) and lateral PTS (LPTS) contribute to ACLR outcomes, but the clinical importance of their difference-delta angle-has not been previously explored. The delta angle, or the difference between the lateral and medial PTSs, is a more significant predictor of ACLR rerupture than either slope considered individually. Case series; Level of evidence, 4. The authors conducted a retrospective analysis of the medical records of 1174 patients who underwent primary, contralateral, or revision ACLR from 2007 to 2018 at a single institution. Medial and lateral PTSs were measured on lateral knee radiographs, and the delta angle was calculated as LPTS minus MPTS. Logistic regression analysis was used to assess the association between these variables and ACLR outcomes, adjusting for potential confounders, such as age and sex. The mean delta angle was significantly lower in the primary ACLR group compared with the revision ACLR group (3.1°± 2.3° vs 6.2°± 2.2°; P < .001). Isolated high LPTS was a better predictor of ACLR reruptures than isolated high MPTS. The delta angle was significantly associated with an increased risk of revision surgery (OR, 1.675; 95% CI, 1.618-1.968; P < .001). The delta angle is a crucial risk factor for ACLR failure, with a higher delta angle significantly associated with higher odds of ACLR revision. These findings suggest that consideration of both medial and lateral PTSs, and particularly their difference, should be integral in assessing ACLR risk and planning surgical interventions.