A Novel Magnetic Resonance Imaging Classification of Discoid Lateral Meniscus Based on Peripheral Attachment

Background In the symptomatic discoid lateral meniscus, the effectiveness of preoperative magnetic resonance imaging (MRI) is not well documented. Hypothesis Magnetic resonance imaging classification will provide more information to the surgeon in choosing the appropriate treatment methods with the help of arthroscopic findings. Study design Cohort study (diagnosis); Level of evidence, 2. Methods Sixty-seven patients (82 knees) were reviewed. The preoperative MRI was checked in 76 of 82 knees. The Lysholm and Ikeuchi grading scales were evaluated. Images were analyzed from MRI, and findings were classified into 4 categories: no shift, anterocentral shift, posterocentral shift, and central shift. Tear pattern classifications were based on arthroscopic findings: horizontal tear, peripheral tear, horizontal and peripheral tear, posterolateral corner loss, and others. The correlations between MRI classification tear patterns and surgical methods were analyzed using the chi-square test or the Fisher exact test. The sensitivity, specificity, and accuracy of shift in preoperative MRI—according to the existence of peripheral tear when corroborated with arthroscopy—were also analyzed with the chi-square test. Inter- and intraobserver reliability was statistically analyzed by producing the inter- and intraclass correlation coefficient. Results The mean preoperative Lysholm score was 77.3 (range, 43–97), and the last follow-up Lysholm score had increased to 96.8 (range, 84–100; P < .001). At last follow-up (100% follow-up), the Ikeuchi grading scale scored 48 knees as excellent, 30 as good, and 4 as fair. According to the MRI classification, 43 knees were no shift; 6, anterocentral shift; 15, posterocentral shift; and 12, central shift. Shift-type knees had a significantly larger number of peripheral tears, and repairs were performed in the shift-type knees (55%) more frequently than in the no-shift-type knees (28%). Among 82 knees, 31 were repaired simultaneously after a central partial meniscectomy. Conclusion Magnetic resonance imaging classification provides more information to surgeons in choosing the appropriate treatment methods, although the final decision regarding procedure is made during arthroscopy after thorough analysis of the tear.