Combined use of cleft and truncated triangle signs helps improve the preoperative MRI diagnosis of lateral meniscus posterior root tears in patients with ACL injuries

Purpose: This study aimed to investigate whether combining the analysis of different magnetic resonance imaging (MRI) signs enhances the diagnostic accuracy of lateral meniscus posterior root tears (LMPRTs) in patients with anterior cruciate ligament (ACL) injuries. We hypothesised that analysing the cleft, ghost and truncated triangle signs and lateral meniscus extrusion (LME) measurement together would improve the preoperative MRI-based diagnosis of LMPRTs. Methods: This retrospective study used prospectively collected registry data from two academic centres, including patients undergoing primary or revision ACL reconstruction (ACLR) and LMPRT repair. The control group included age- and sex-matched (1:1) patients undergoing ACLR without any lateral meniscus tears. LME (mm) and the presence of cleft, ghost and/or truncated triangle signs were evaluated using preoperative MRI. Results: In total, 252 patients (126 per group) were included. Individually, the cleft and truncated triangle signs achieved the highest sensitivity (60% and 62%, respectively) and accuracy (>89%). The presence of either sign increased sensitivity to 79% and enabled the correct classification of 93% of ACL injuries as having or not having an LMPRT, with high specificity (95%) and good positive predictive value (74%). This combination was considered the most efficient in reducing false positives and false negatives. The LME (cutoff value: 2.2 mm) and ghost sign had lower sensitivities (50% and 14%, respectively) and accuracies (83% and 87%) and were not part of the optimal combination. Conclusion: The cleft and/or truncated triangle signs on preoperative MRI reliably detected 79% of LMPRTs in this cohort, with high specificity (95%) and good positive predictive value (74%). This combination provides an effective method for achieving reasonable sensitivity while minimising false positives, aiding surgeons in preoperative diagnosis and planning for LMPRT repair. Level of Evidence: Level III.