Electrophysiologic study of the anterior interosseous nerve

Nerve conduction studies of the anterior interosseous nerve were performed on 26 healthy subjects (6 women and 20 men, aged 24 to 63 years). The compound muscle action potential from the pronator quadratus muscle was obtained by using surface electrodes placed over the dorsal aspect of the distal forearm and median nerve stimulation at the elbow. The latency of the evoked potential was determined over distances that ranged from 17.5-28 cm from the elbow to the pronator quadratus muscle; this resulted in latencies of 3.5 ms (+/- 0.4) and 3.6 ms (+/- 0.4) for the left and right extremities, respectively, with a side-to-side difference of 0.1 ms (+/- 0.1). The amplitude of the potentials recorded was 3.1 mV (+/- 0.8); a difference in amplitude of 11.4% (+/- 7.7%) between extremities was seen. Although duration measurements were obtained, the frequent presence of biomodal peaks made interpretation difficult. This bimodal pattern was felt to represent either two heads of the pronator quadratus or another muscle innervated by the anterior interosseous nerve. The technique in the present study is easy to perform, allows better assessment of the compound muscle action potentials obtained and provides for side-to-side comparisons of latency and amplitude. This technique aids the electromyographer in evaluation of suspected cases of injury to the anterior interosseous nerve, particularly in unilateral cases.