Lesions of the anterior interosseous nerve in the forearm are rare and often misdiagnosed as tendon injuries. A consecutive series of 13 patients with this condition referred for electrodiagnosis is reviewed. Only three had originally a correct clinical diagnosis and three were initially considered to have tendon ruptures.

Five cases were of mechanical origin and seven due to ‘neuritis’. All showed electrophysiological abnormalities, most commonly involving the pronator quadratus. Late spontaneous recovery was common, and only one case had surgical exploration.

Twenty-two patients with ulnar nerve palsy at the elbow, confirmed by electromyography, were treated by a night splint which prevented flexion of the elbow beyond 60 degrees. The splint was worn all night regularly for at least six months. At a mean follow-up of 11.3 months, 17 patients had clinical and electromyographic assessment and five were contacted by telephone. There was improvement in the symptoms in every patient, including three who had failed to respond to surgical decompression. There was electromyographic improvement in 16 of the 17 patients re-examined at follow-up. The mean improvement in motor nerve conduction velocity was 6.5 m/s and in sensory nerve conduction velocity 9.5 m/s. The efficacy of this treatment suggests that nocturnal elbow flexion is an important cause of ulnar nerve lesions at the elbow.