Electrodiagnosis of ulnar nerve lesions at the elbow.

To determine electrical criteria which might be helpful in the diagnosis of ulnar nerve entrapment at the elbow, clinical and electrodiagnostic features in 78 patients with suspected ulnar nerve entrapment at the elbow are described and compared to the results of sensory and motor conduction in the ulnar nerve in a control group of normal persons. These criteria include (1) absent or abnormal evoked sensory nerve action potential in the little finger, (2) motor conduction velocity of less than 45.0 meters/sec in across elbow segment of the ulnar nerve with elbow flexed at 35 degrees, and (3) abnormal electromyographic findings including the presence of increased insertional activity or signs of denervation in the first dorsal interosseous, abductor digiti minimi, and/or flexor carpi ulnaris muscles. Electromyographic abnormality was seen in 77.5% of patients with ulnar motor conduction velocity of less than 45.0 meters/sec across the elbow. The first dorsal interosseous was the most commonly affected muscle. A study of certain important anatomic and histologic factors, such as the arrangement and relative concentration of the motor and sensory fibers at certain key points inthe course of the ulnar nerve trunk, is necessary to understand the correlation between the clinicopathologic and electrodiagnostic features in patients with ulnar nerve entrapment at the elbow.