A new indirect magnetic resonance imaging finding in anterior cruciate ligament injuries: Medial and lateral meniscus posterior base angle

OBJECTIVES: This study aimed to define the medial meniscus posterior base angle (MMPBA) and the lateral meniscus posterior base angle (LMPBA) measured in the medial and lateral meniscus posterior horns and examine the biomechanical and morphological relationship between anterior cruciate ligament (ACL) injuries and posterior meniscus horns using these parameters. PATIENTS AND METHODS: The retrospective study was conducted with 32 patients with ACL rupture and 40 control patients, for a total of 72 patients (40 males, 32 females; mean age: 36.3±9.9 years; range, 18 to 57 years), between January 2016 and January 2018. The posterior tibial slope (PTS) was measured in standard radiographs, and MMPBA and LMPBA values were assessed by standard knee magnetic resonance imaging. The MMPBA was defined as the angle between the line passing through the medial meniscus’ tibial side border and the line passing through the capsular side border in the sagittal section's medial meniscus posterior horn. The LMPBA was defined as the angle between the line passing through the lateral meniscus' tibial side border and the line passing through the capsular side border on the sagittal section's lateral meniscus posterior horn. Groups were compared for PTS, MMPBA, and LMPBA. RESULTS: When both groups were compared in terms of MMPBA and LMPBA, patients with ACL rupture had significantly higher base angles (p<0.001 and p=0.031, respectively). The mean MMPBA was 84.27º±12.59º (range, 62º to 106.1º) in patients with ACL rupture, while it was 70.75º±7.85º (range, 55.1º to 88.6º) in the control group. The mean LMPBA was 83.62º±11.4º (range, 62.3º to 105.9º) in patients with ACL rupture, while it was 76.94º±11.46º (range, 30.8º to 96.5º) in the control group. In the receiver operating characteristics curve analysis, the cut-off value of MMPBA was 84.5, and values above this showed a 58.5% sensitivity and a 97.6% specificity for ACL rupture, whereas for LMPBA, the cut-off value was 93.15, and values above this showed a 27.3% sensitivity and a 95.1% specificity for ACL rupture. The PTS and MMPBA were significantly correlated with each other (p=0.047). The MMPBA and LMPBA were also significantly correlated with each other (p=0.011). However, there was no significant correlation between PTS and LMPBA (p=0.56). CONCLUSION: Medial meniscus posterior base angle and LMPBA values above 84.5º and 93.15º, respectively, are new indirect magnetic resonance imaging findings of ACL injury.