Lateral meniscus posterior root tear in anterior cruciate ligament injury can be detected using MRI-specific signs in combination but not individually

Purpose The purpose of this study was to evaluate (1) the diagnostic value of using single and multiple magnetic resonance imaging (MRI) findings for lateral meniscus posterior root tear (LMPRT) detection in anterior cruciate ligament (ACL) injury and (2) the influence of time from ACL injury to MRI assessment on LMPRT detection. Finally, we investigated the relationship between LMPRT and bone bruising. Methods In all, 231 knees with ACL injury, 32 with LMPRT, were retrospectively assessed. Cases were evaluated for LMPRT based on the cleft, ghost, and truncated triangle signs, used individually or in combination. To assess the influence of the timing of the MRI assessment on LMPRT detection, we also evaluated the overall sensitivity, specificity, and accuracy in cases in which MRI was performed within 2 weeks of injury. The number of condyles with bone bruising was assessed and then compared between patients with and without LMPRT. Results Although the sensitivity and specificity of the three signs individually were 34.4-65.6% and 94.0-97.0%, when at least one of these signs was positive, the sensitivity and specificity were 84.4% and 90.5%, respectively. However, the diagnostic value of each sign when MRI was performed within 2 weeks of injury was lower than the overall value. There was a significant difference in the number of condyles with bone bruising between the LMPRT (3 +/- 1) and non-LMPRT (2 +/- 2) groups. Conclusions Although the sensitivity of each sign for LMPRT was low, LMPRT could be detected adequately if these signs were used in combination. Therefore, surgeons should detect LMPRT using these three signs in combination, not individually.