MRI evaluation of hypermobile lateral meniscus beyond distance measurements: the role of integrated popliteomeniscal fascicle assessment.

backgroundHypermobile lateral meniscus (HLM) causes lateral knee pain and mechanical symptoms, but preoperative identification remains challenging because HLM is a dynamic abnormality that is not always captured on static magnetic resonance imaging (MRI). Previous MRI-based studies have mainly focused on linear measurements or qualitative popliteomeniscal fascicle (PMF) abnormalities. This study aimed to evaluate whether spatial MRI assessment beyond conventional linear distance measurements could help characterize arthroscopically confirmed HLM. We also aimed to determine whether MRI-derived markers could be organized into a clinically interpretable MRI-based approach to raise preoperative suspicion for HLM.

methodsThis retrospective study included patients who underwent knee MRI followed by arthroscopic assessment of lateral meniscal stability. After propensity score matching, 53 knees with arthroscopically confirmed HLM and 53 non-HLM surgical controls were analyzed. MRI-derived variables included LM-popliteal tendon distance, region-of-interest-based measurement, MRI signal intensity ratio, and PMF integrity. Each PMF was evaluated separately and then summed to obtain the combined PMF score. Firth's logistic regression, receiver operating characteristic curve, and Youden index analysis were performed.

resultsStatic measurements of LM-popliteal tendon separation did not differ between groups. In contrast, the sagittal MRI signal intensity ratio (odds ratio [OR], 1.067; 95% confidence interval [CI] 1.012-1.137; p = 0.044) and the combined PMF score were significantly associated with HLM (OR, 0.098; 95% CI 0.034-0.257; p < 0.001) were significantly associated with HLM in univariable analysis. In multivariable analysis, only the combined PMF score remained independently associated with HLM. The PMF score-only model showed an area under the curve of 0.794 (95% CI 0.709-0.879), with a Youden-derived threshold of ≤ 1.0, sensitivity of 58.5%, specificity of 86.8%, and accuracy of 72.6%.

conclusionsThe combined PMF score was the MRI-derived marker most consistently associated with arthroscopically confirmed HLM. In this selected surgical cohort, lower combined PMF scores showed acceptable discrimination and relatively high specificity, although sensitivity was modest. Accordingly, a combined PMF score of ≤ 1.0 may provide adjunctive MRI information that raises suspicion for HLM when the clinical presentation is suggestive, but it cannot exclude HLM or independently establish the diagnosis, and the decision to perform arthroscopy should not be based on the score alone. Arthroscopic dynamic assessment remains necessary for definitive confirmation.