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 tunnel with noninvasive magnetic resonance imaging (MRI). We used fresh human cadavers with the elbow in full extension, 90 degrees of flexion, and full flexion. For each elbow, 1-mm slices were imaged interpolated, and reconstructed into 3-dimensional data volumes, and then manually segmented before they were examined with sequential transverse sections, curved sections, and 3-dimensional images. The ulnar nerve follows a tortuous course in full extension, becomes progressively linear with incremental elbow flexion, shifts anteriorly in the cubital tunnel, and flattens against the medial epicondyle. The proximal and midportions of the cubital tunnel also change with flexion from round to elliptical. In 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 observations suggest that the ulnar nerve progressively stretch over the medial epicondyle occurs when the normal elbow is flexed. Direct compression areas of the ulnar nerve were not seen in our study of normal human elbows.