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Morton Neuroma: MR Imaging in Prone, Supine, and Upright Weight-bearing Body Positions¹

¹ From the Institute of Diagnostic Radiology, University Hospital, Rämistrasse 100, CH-8091 Zurich, Switzerland (D.W., K.T., J.K.W., B.M.); Orthopedic Practice, Zurich, Switzerland (H.P.K., H.Z.); and Departments of Orthopedic Surgery (P.V.) and Radiology (J.H., M.Z.), Orthopedic University Hospital Balgrist, Zurich, Switzerland. Received November 26, 2001; revision requested February 8, 2002; final revision received May 29; accepted July 15. Address correspondence to D.W. (e-mail: dominik.weishaupt@dmr.usz.ch).

PURPOSE: To assess the effect of prone, supine, and upright weight-bearing body positions on visibility, position, shape, and size of Morton neuroma during magnetic resonance (MR) imaging.

MATERIALS AND METHODS: Eighteen patients with 20 Morton neuromas underwent MR imaging of the forefoot in prone (plantar flexion of the foot), supine (dorsiflexion of the foot), and upright weight-bearing positions. Visibility (3 = good, 2 = moderate, 1 = poor), position relative to the metatarsal bone, shape, and transverse diameter of Morton neuroma were assessed on transverse T1-weighted MR images. Associations between different body positions and variables of interest were calculated with Wilcoxon signed rank test, ² test, and paired Student t test.

RESULTS: In the prone position, visibility of all 20 Morton neuromas was rated with a score of 3; visibility in the supine and weight-bearing positions was inferior (mean score, 2.4). All 20 (100%) Morton neuromas changed their position relative to the metatarsal bone between prone and supine and between prone and weight-bearing positions. When compared with the prone position, there was a difference in the shape of all 20 Morton neuromas in the weight-bearing position (P < .001). Between prone (mean transverse diameter of Morton neuroma, 8 mm) and supine (mean transverse diameter of Morton neuroma, 6 mm) positions, the transverse diameter of Morton neuroma significantly decreased by 2 mm (P = .03); between prone and weight-bearing positions, the decrease of the mean transverse diameter was also significant (difference, 2 mm; P = .03).

CONCLUSION: Morton neuroma appears significantly different during MR imaging in prone, supine, or weight-bearing positions. The transverse diameter of Morton neuroma is significantly larger on images obtained in the prone position than it is on images obtained in the supine and upright weight-bearing positions. Visibility of Morton neuroma is best on MR images obtained in the prone position.

© RSNA, 2003

Index terms: Efficacy study • Foot, MR, 465.121411 • Foot, neoplasms, 465.315, 465.369 • Neuroma, 465.315, 465.369