Evaluation of Meniscal Subluxation of the Knee with MR Imaging

Abstract

Purpose: The purpose of this study was to determine the normal meniscal position and meniscal subluxation by means of MR imaging. Materials and Methods: The normal position of the meniscus was determined by measuring the distance between the peripheral meniscal borders and the tibial plateau, as seen on coronal, sagittal and oblique MR images of 40 normal knees. For 33 abnormal knees in which outward subluxation of the meniscus from the tibial plateau was noted, the involved site, the predisposing factor, and the frequency of meniscus tearing were analyzed. Results: In normal knees, the peripheral border of the meniscus extruded 3 mm or less from the peripheral border of the tibial plateau. Among 33 abnormal knees, in which 5 mm or more outward subluxation of the meniscus was seen, 19 menisci were medial and 14 were lateral. Among the 19, the body was involved in 12, the anterior horn in six, and the posterior horn in one. With regard to the 14 lateral subluxations, involvement of the posterior horn occurred in ten, of both the body and posterior horn in two, of the anterior horn in one, and of the body in one. The common predisposing factor in medial meniscus subluxation was osteoarthritis, seen in 89% of such cases, and in lateral subluxation, anterior cruciate ligament tear, which occurred in 79% of cases. Medial meniscus tear was noted in 89% of medial meniscus subluxations and lateral meniscus tear in 43% of lateral subluxations. Conclusion: Meniscal subluxation was easily detected by MR imaging of the knee. The common predisposing factor in medial meniscus subluxation was osteoarthritis, and in lateral meniscus subluxation, anterior cruciate ligament tear. A torn meniscus frequently cooccurred.