Increased lateral posterior tibial slope and greater tibiofemoral rotation are associated with a higher risk of lateral meniscal tears in anterior cruciate ligament injuries

BACKGROUND: Lateral meniscal (LM) tears are common in anterior cruciate ligament (ACL)-injured knees but may be underestimated on preoperative magnetic resonance imaging. Structural imaging parameters reflecting knee morphology and alignment may help identify patients at increased risk of LM injury. This study examined whether medial posterior tibial slope (MPTS), lateral posterior tibial slope (LPTS), and tibiofemoral rotation angle (TFA) are associated with LM tears in ACL injuries. METHODS: This retrospective cohort study evaluated clinical records and preoperative magnetic resonance imaging (MRI) scans of patients undergoing primary ACL reconstruction. MPTS, LPTS, TFA, and delta angle were measured on standardized MRI, and LM status was confirmed arthroscopically. Multivariable logistic regression analysis identified independent associations. Restricted cubic spline (RCS) analysis assessed nonlinear dose-response patterns, and receiver operating characteristic (ROC) curves with DeLong testing quantified incremental predictive performance. RESULTS: A total of 215 patients were included (100 with and 115 without LM tears). Patients with tears demonstrated greater LPTS (5.9 ± 3.9° vs 4.5 ± 3.4°, p = 0.005) and TFA (2.3 ± 4.7° vs 1.0 ± 3.1°, p = 0.015), while MPTS and delta angle did not differ. After adjustment, LPTS (odds ratio [OR], 1.12; 95% confidence interval [CI], 1.03-1.21; p = 0.007), MPTS (OR, 2.48; 95% CI, 1.24-5.07; p = 0.011), and TFA (OR, 1.10; 95% CI, 1.02-1.18; p = 0.014) remained independently associated with LM tears. RCS analysis revealed a nonlinear, right-shifted U-shaped association between TFA and tear risk (P-nonlinearity < 0.001), with risk increasing at extreme rotational values, particularly increasing internal tibial rotation. ROC analysis showed modest improvements in discrimination with LPTS (area under the curve [AUC], 0.600 to 0.665; p = 0.041) and TFA tertiles (AUC, 0.600 to 0.674; p = 0.040); however, overall discrimination remained limited and these findings should be interpreted cautiously without external validation. CONCLUSION: Steeper lateral posterior tibial slope and greater tibiofemoral rotation were independent risk factors for LM tears in anterior cruciate ligament injuries. Tibiofemoral rotation showed a nonlinear increase in risk, driven mainly by excessive internal rotation. These parameters may provide additional context for preoperative risk stratification.