MR imaging of the knee: position related changes of the menisci in asymptomatic volunteers

RATIONALE AND OBJECTIVES: To evaluate position related changes of the menisci in asymptomatic volunteers based on MR imaging of the knee in different positions. METHODS: Twenty-two knees from 22 asymptomatic volunteers with no history of knee injury and no evidence of meniscal tears were examined with a 0.5-T open-configuration MR system. Sagittal and coronal images were obtained with the knee supine in neutral, supine in 90-degree flexion with external and internal rotation, as well as in upright weight-bearing positions. The position of the menisci from the outer inferior edge of the meniscus to the outermost edge of the articular cartilage of the tibial plateau was measured, and meniscal movement was calculated. The Wilcoxon signed-rank test was used for statistical analysis. RESULTS: Meniscal movement in the sagittal plane was greatest in the anterior horn of the medial meniscus upon position change from supine neutral to supine in 90-degree flexion with external rotation (mean, 10.5 millimeters). The least meniscal movement was observed in the anterior horn of the lateral meniscus when changing from the supine neutral to the upright knee position (mean, 0.6 millimeters). Meniscal protrusion (ie, protrusion of any part of the meniscus beyond the tibial plateau) was noted most frequently for the anterior horn of the medial meniscus (14/22 instances; 63.6%) in the sagittal plane with the knee in neutral position (mean, 2.6 millimeters, range, 1.8-2.8 millimeters). In the coronal plane, medial meniscal protrusion was most frequently present in the upright weight-bearing position (11/22 instances (50%; mean, 2 millimeters; range, 1.2-2.6 millimeters). CONCLUSIONS:: Meniscal movement is most prominent in the anterior horn of the medial meniscus with the knee in the supine position in 90-degree flexion with external rotation. Meniscal protrusion is more frequently present in the medial meniscus and averaged less than 3 millimeters in normal volunteers in either the sagittal or coronal MR imaging plane.