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° to 90° to 120° 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.