MORPHOLOGIC CHANGES IN THE ULNAR NERVE AT THE ELBOW WITH FLEXION AND EXTENSION - A MAGNETIC-RESONANCE-IMAGING STUDY WITH 3-DIMENSIONAL RECONSTRUCTION

We evaluated the morphology of the ulnar nerve and cubital funnel with noninvasive magnetic resonance imaging (MRI). We used fresh human cad avers with the elbow in full extension, 90 degrees of Flexion, and ful l flexion. For each elbow, T-mm slices were imaged interpolated, and r econstructed into 3-dimensional data volumes, and then manually segmen ted before they were examined with sequential transverse sections, cur ved sections, and 3-dimensional images. The ulnar nerve follows a tort uous course in full extension, becomes progressively linear with incre mental elbow flexion, shifts anteriorly in the cubical tunnel, and fla ttens against the medial epicondyle. The proximal and midportions of t he cubital funnel also change with flexion From round to elliptical. I n addition, successive increases occur in the cross-sectional diameter of the mediolateral plane. The nerve is surrounded by fat throughout the cubital tunnel except adjacent to the medial epicondyle. These obs ervations suggest that the ulnar nerve progressively stretch over the medial epicondyle occurs when the normal elbow is flexed Direct compre ssion areas of the ulnar nerve were not seen in our study of normal hu man elbows.