Strain on the ulnar nerve at the elbow and wrist during throwing motion

Background: It is well known that cubital tunnel syndrome frequently occurs in throwing athletes. The cause of cubital tunnel syndrome is considered to be mechanical stimuli on the ulnar nerve in the cubital tunnel. The hypothesis of the present cadaveric study was that the ulnar nerve is subjected to longitudinal strain in the cubital tunnel during the throwing motion. Methods: Four phases of throwing (stance, wind-up, middle cock-up, and early acceleration) were passively simulated in seven fresh-frozen transthoracic cadaveric specimens that were fixed in an upright position to allow free arm movement. In each throwing phase, the elbow was sequentially flexed from 45 degrees to 90 degrees to 120 degrees to maximum flexion. The longitudinal movement of and strain on the ulnar nerve were measured with use of a caliper and a strain gauge at the proximal aspects of both the cubital tunnel and the canal of Guyon. Results: The movement of the ulnar nerve at the proximal aspect of the cubital tunnel was significantly increased during all throwing phases with increased elbow flexion (p < 0.05). An average maximum movement of 12.4 +/- 2.4 mm was recorded during the wind-up phase with maximum elbow flexion. The movement at the proximal aspect of the canal of Guyon was approximately two-thirds of that at the proximal aspect of the cubital tunnel. The strain on the ulnar nerve at the proximal aspect of the cubital tunnel was significantly increased with elbow flexion in the stance, wind-up, and middle cock-up phases (p < 0.05). An average maximum strain of 13.1% +/- 6.1% was recorded during the early acceleration phase with maximum elbow flexion. The strain at the proximal aspect of the canal of Guyon was approximately half of that at the proximal aspect of the cubital tunnel. Conclusions: In the present study, the maximum strain on the ulnar nerve during the acceleration phase was found to be close to the elastic and circulatory limits of the nerve. Clinical Relevance: The results of the present in vitro cadaveric study suggest that acute and repetitive strain on the ulnar nerve produced by frequent throwing motion may be sufficient to injure the structure and microcirculation of the nerve.