Medial–lateral posterior tibial slope asymmetry is associated with the presence of medial meniscus posterior root tear

BACKGROUND: Posterior tibial slope (PTS) has been identified as an important anatomical risk factor for medial meniscus posterior root tear (MMPRT). However, prior studies have primarily focused on the medial slope. The primary aim of this study was to measure medial and lateral PTS on magnetic resonance imaging (MRI) and to determine whether medial-lateral slope asymmetry is associated with MMPRT. METHODS: This multicenter retrospective study included patients aged 50-75 years who underwent knee MRI for knee pain at two institutions. Patients with osteoarthritis (Kellgren-Lawrence grade 3 or 4) were excluded. MMPRT was diagnosed on MRI. The medial PTS (MPTS), lateral PTS (LPTS), medial proximal tibial angle (MPTA), and lateral distal femoral angle (LDFA) were measured, and ΔPTS was defined as MPTS - LPTS. Groups were compared before and after 1:1 propensity score (PS) matching for age, sex, and body mass index. Multivariable logistic regression and receiver operating characteristic (ROC) curve analysis were conducted to evaluate the association and discriminative ability of ΔPTS. RESULTS: A total of 120 knees were included, of which 26 (21.7%) demonstrated MMPRT. MPTS did not differ significantly between groups, whereas the MMPRT group showed a significantly smaller LPTS (p < 0.001) and larger ΔPTS (p < 0.001). These findings remained consistent after 1:1 PS matching (22 matched pairs), with ΔPTS remaining significantly greater in the MMPRT group (p < 0.001). In multivariable analysis, ΔPTS was independently associated with MMPRT (odds ratio 2.17 per 1°, 95% CI 1.56-3.02, p < 0.001). ROC curve analysis demonstrated good discriminative performance of ΔPTS for identifying MMPRT (area under the curve [AUC] = 0.87, 95% CI 0.79-0.95), which exceeded that of LPTS (0.73) and MPTS (0.54) (DeLong p = 0.006 and p < 0.001, respectively). The exploratory cutoff value was 4.0°, yielding a sensitivity of 80.8% and a specificity of 81.9%. CONCLUSIONS: Knees with MMPRT exhibited a smaller LPTS and greater ΔPTS compared with knees without MMPRT, which remained significant after PS matching. ROC analysis demonstrated good discriminative performance, and a ΔPTS of 4.0° or greater may serve as an exploratory threshold. PTS asymmetry may represent a morphological factor associated with MMPRT.