Magnetic Resonance Imaging Measurements of Maximum Thickness of Medial Meniscus Exceeding 10 mm Are Strongly Associated With Medial Meniscus Posterior Root Tear.

PURPOSE: To evaluate the diagnostic utility of measuring the maximum thickness of the medial meniscus (MTMM) for detecting medial meniscus posterior root tear (MMPRT).

METHODS

This retrospective study evaluated patients with medial meniscus (MM) injuries who underwent arthroscopic procedures between January 2018 and February 2024. Patients with concomitant lateral meniscal injuries, ligament injuries, or a history of knee trauma were excluded. MTMM was measured as the maximum vertical length in the coronal plane, identified by systematically measuring all slices using digital calipers on proton density-weighted fat-suppressed magnetic resonance imaging sequences. A reference group consisted of anterior cruciate ligament reconstruction patients with no meniscal injuries confirmed during arthroscopy. Statistical analyses were performed to examine the relationships between MTMM and meniscal injury patterns.

RESULTS

The study included 35 MMPRT patients (mean age, 56.9 years), 138 other MM injuries (51.8 years), and 60 reference patients undergoing anterior cruciate ligament reconstruction (28.4 years). MTMM was significantly greater in the MMPRT group compared to other MM injuries (10.7 ± 1.5 mm vs 8.1 ± 1.4 mm, P < .05) and intact medial meniscus (7.1 ± 0.9 mm, P < .05). Receiver operating characteristic analysis identified an optimal cutoff value of 10.05 mm (sensitivity, 77.1%; specificity, 92.8%; area under the curve, 0.906). Based on this analysis, MTMM >10 mm was designated as the "thickened meniscus sign." Twenty-seven of 35 MMPRT cases showed a positive thickened meniscus sign, while no cases in the reference group exceeded this threshold.

CONCLUSIONS

MTMM was significantly greater in MMPRT cases compared to other MM injuries. The thickened meniscus sign (MTMM >10 mm) had high diagnostic performance with 92.8% specificity, providing a simple and reliable screening tool for MMPRT detection.

LEVEL OF EVIDENCE: Level Ⅲ, retrospective diagnostic study.