Ulnar nerve entrapment at the elbow localized by short segment stimulation.

The purpose of the study was to evaluate the differences in the amplitudes of the compound muscle action potentials of the hypothenar muscles and the differences in conduction times. Differences in shoot segment responses were determined by stimulating the ulnar nerve at 2-cm intervals across the elbow in 20 normal adults. Thirteen ulnar nerves on the left side and 12 nerves on the right of 14 men and six women were studied for motor nerve conduction velocity. The amplitudes of the hypothenar compound muscle action potentials and the conduction times after supramaximal stimulation of the ulnar nerve were also determined. The distal-to-proximal reduction in the amplitude of the potentials was 6% on the left and 4.2% on the right. The maximum conduction time in a 2-cm segment on the right side was 0.63msec (mean +2SD = 0.43 + 0.20) and on the left, 0.60msec (mean +2SD = 0.44 + 0.16). Using the same short segment stimulation technique, ulnar nerve motor conduction was also studied in 13 patients with suspected ulnar neuropathy at the elbow in order to localize the nerve lesion. Conduction time only was abnormal in one patient, both conduction time and amplitude in nine, amplitude only in one, and conduction time and mild reduction in amplitude in two. It was concluded that short segment stimulation of the ulnar nerve at the elbow is useful in localizing the exact site of entrapment/compression of the nerve at the elbow.