Diagnostic criterion to distinguish between incomplete and complete discoid lateral meniscus on MRI

Purpose To determine a new cutoff value that can further distinguish between the incomplete and complete discoid lateral meniscus (DLM). Materials and Methods Twenty‐one cases of incomplete DLM and 42 cases of complete DLM without tear were included. In all, 105 patients with normal lateral menisci were included as a control group. We measured the ratio of the shortest width of the lateral meniscus to the longest width of the tibia (ratio 1) and the ratio of the shortest width of the medial meniscus to the shortest width of the lateral meniscus (ratio 2). Results By applying a cutoff value of ratio 1 as 0.32 between two incomplete and complete DLM groups, the proportion of the complete and incomplete DLM diagnosed cases among the true cases were 84% and 94%, respectively. By applying a cutoff value of ratio 2 as 0.40 between two incomplete and complete DLM groups, the proportion of the complete and incomplete DLM diagnosed cases among the true cases were 84% and 75%, respectively. Conclusion A cutoff value of 0.32 using the ratio of the shortest width of the lateral meniscus and the longest width of the tibia are probably useful to help distinguish between complete DLM and incomplete DLM. Additionally, the new ratio using the width of the medial meniscus is also useful to improve distinguishing between the types of DLM. J. Magn. Reson. Imaging 2013;38:417–421. © 2013 Wiley Periodicals, Inc.