Error patterns in the MR imaging evaluation of menisci of the knee.

Abstract

To categorize errors in interpretation of magnetic resonance (MR) images of the knee and explain the discrepancy between MR imaging and diagnostic arthroscopic findings. Five hundred sixty-one patients underwent arthroscopy and MR imaging of the knee. Prospective and retrospective readings were used to categorize tear type and location. Sixty-six patients had 68 discrepancies between MR imaging and arthroscopic findings. Prospective interpretation of MR images of the lateral meniscus had a sensitivity of 82%, specificity of 98%, and accuracy of 93%. For images of the medial meniscus, sensitivity was 96%; specificity, 91%; and accuracy, 95%. The number of diagnostic errors at retrospective analysis was 76% (n = 52) of the number at prospective analysis. MR imaging is accurate in evaluation for meniscal tears. Most errors in interpretation that occur at prospective evaluation also occur at retrospective evaluation. Some false-positive errors may be related to incomplete arthroscopic evaluation of the meniscus and confusion between what represents fraying and what represents a tear.