Lateral Tibial Slope on Pre-Reconstruction MRI in ACL Graft Rerupture: Association, Discriminative Performance, and Measurement Reliability

Background/Objectives: This study evaluated the association between lateral tibial slope (LTS), measured using the Hudek method on magnetic resonance imaging (MRI) before primary anterior cruciate ligament (ACL) reconstruction, and ACL graft rerupture, and assessed the discriminative performance and reliability. Methods: This retrospective comparative study included 23 patients with definite ACL graft rerupture and 46 controls without rerupture after at least two years of follow-up. LTS was independently measured twice, four weeks apart, by a radiologist and an orthopedic surgeon blinded to group allocation and clinical outcomes. Reliability was assessed using intraclass correlation coefficients (ICCs), interobserver agreement using Bland–Altman analysis, and discriminative performance using receiver operating characteristic (ROC) analysis. Age-adjusted associations with rerupture were evaluated using logistic regression. Results: LTS was significantly higher in the rerupture group in both measurement rounds for both observers (all p ≤ 0.009). Intraobserver repeatability was excellent for the radiologist (ICC = 0.985) and good for the orthopedic surgeon (ICC = 0.852), while interobserver agreement was moderate (ICC = 0.547 for mean measurements). The orthopedic surgeon measured LTS 0.85° higher on average. The area under the ROC curve was 0.794 (95% CI, 0.678–0.910) for the radiologist and 0.700 (95% CI, 0.563–0.837) for the orthopedic surgeon. Exploratory thresholds of ≥4.3° and ≥5.4° showed sensitivities of 60.9% and 43.5% and specificities of 93.5% and 91.3%, respectively. After age adjustment, each 1° increase in LTS was associated with 1.682-fold and 1.412-fold higher odds of rerupture (both p ≤ 0.003). Conclusions: Higher LTS before primary ACL reconstruction was associated with graft rerupture, including after age adjustment. Observer-related differences may influence absolute measurements and derived thresholds. Given their high specificity but limited sensitivity, these exploratory thresholds should not be considered validated clinical decision cutoffs.