Decreased medial posterior tibial slope is associated with an increased risk of posterior cruciate ligament rupture

Purpose It remains unclear whether there is an association between posterior cruciate ligament (PCL) rupture and the medial posterior tibial slope (MTS) or lateral posterior tibial slope (LTS). The present case–control study aimed to investigate a possible association between primary PCL rupture and MTS or LTS measured by magnetic resonance imaging (MRI). Methods A retrospective case–control study was conducted. Patients with primary PCL ruptures but not with anterior cruciate ligament injuries, were 1:1 matched by age and sex to a control group with no evidence of knee ligament injuries. Knee MRI was used to measure the MTS and LTS. In addition, the receiver operating characteristic (ROC) analysis was performed to identify an optimal cut-off value of the MTS and/or LTS. Results In total, 46 patients with PCL ruptures (32 males, 14 females) and 46 controls (32 males, 14 females) were included in this study. The MTS was significantly lower in the patients with PCL ruptures (3.0° ± 2.2°) than in the control group (5.1° ± 2.3°, p < 0.001). The mean LTS/MTS ratio was significantly higher in patients with PCL ruptures (2.6 ± 2.5) than in the control group (1.3 ± 1.3, p = 0.001). However, the LTS was not significantly different between patients with PCL ruptures and the controls (4.4° ± 2.3° vs. 5.3° ± 2.6°, n.s.). After the MTS was determined to be a significant predictor, the ROC analysis was performed. The ROC analysis revealed the most accurate MTS cut-off of < 3.9°, with a sensitivity of 76.1% and a specificity of 73.9%. Conclusion A decreased MTS and an increased LTS/MTS ratio are associated with an increased risk of primary PCL rupture. People with MTS < 3.9° are particularly at risk for PCL ruptures, and prevention and intervention programs for PCL ruptures should be developed and targeted towards them. Levels of evidence Level III.