Ultrasonographic swelling ratio in the diagnosis of ulnar neuropathy at the elbow.

High-resolution ultrasound can demonstrate focal nerve enlargement in entrapment neuropathies. We hypothesized that a ratio between the nerve cross-sectional area at the site of maximal enlargement and at an unaffected site may improve diagnostic accuracy in ulnar neuropathy at the elbow (UNE), when compared to a single measurement at the site of maximal enlargement. Ultrasound was used to measure the cross-sectional area of the ulnar nerve at three sites in 30 normal, healthy controls and 26 individuals with UNE. In individuals with UNE, the ratio was 2.9:1 when the site of maximal swelling was compared with a distal ulnar nerve site and 2.8:1 when compared with a proximal site. This represented a significant increase compared with the ratio of 1.1:1 for both comparisons in controls (P < 0.0001). This type of ratio may be particularly useful for assessing entrapment in those with polyneuropathy or obesity, both of which can cause diffuse nerve enlargement.