Summary A loss of functional motor axons in the median and ulnar nerves occurred in half of thirty-three patients with rheumatoid arthritis. Weakness of small hand muscles may predispose to the development of ulnar deviation of the fingers in patients with joint disease at the radio-ulnar and metacarpophalangeal joints. There is no evidence that spasm of small hand muscles is a significant cause of ulnar deviation of the fingers in rheumatoid arthritis. Ulnar deviation of the fingers in rheumatoid arthritis is not due to selective impairment of the ulnar nerve or the deep palmar branch of the ulnar nerve even though ulnar deviation of the fingers can occur in association with such lesions and in the absence of joint disease.
