MR-IMAGING OF TEARS OF DISCOID LATERAL MENISCI

OBJECTIVE. The purpose of this study was to determine the positive pre dictive value (PPV) for diagnosis of discoid lateral meniscal tear usi ng MR imaging and to describe various patterns of such tears in the kn ee. SUBJECTS AND METHODS. MR reports of 77 patients (10-67 years old) who underwent prospective MR imaging that led to a diagnosis of discoi d lateral meniscal tear were correlated with arthroscopic results. MR images obtained in 71 patients confirmed to have discoid lateral menis cial tear were retrospectively reviewed for the presence, site, and pa ttern of discoid lateral meniscal tear, including type of displacement of the torn segment. MR abnormalities were correlated with arthroscop ic findings. RESULTS. For the prospective MR interpretations, the PPV for discoid meniscus was 92%. PPV for discoid meniscal tear was 57%. P PVs for individual types of discoid meniscal tears were 46% (periphera l tear, 19/41), 76% (peripheral tear with horizontal tears, 16/21), 56 % (horizontal tear, 5/9), 50% (transverse tear, 1/2), 67% (horizontal tear combined with transverse tear, 2/3), and 100% (longitudinal tear, 1/1). Peripheral tear alone and peripheral tear with horizontal tear were the most common types of tears (n = 20, 28%). Multiple tears (n = 34, 48%) were common. Displacement of the torn segments was seen in 5 1 patients (72%). CONCLUSION. MR imaging has a low PPV for diagnosing discoid lateral meniscal tear. Peripheral tear alone and peripheral te ar with horizontal tear were the most common types of tears, and displ acement of the torn segment was frequent.