Anterior translation and morphologic changes of the ulnar nerve at the elbow in adolescent baseball players

The effect of repetitive throwing on the ulnar nerve is not clear. There are no published imaging studies regarding this issue in adolescent baseball players. The purpose of this cross-sectional ultrasonographic study was to use 5- to 10-MHz frequency ultrasonography to define the anterior translation and flattening of the ulnar nerve in different elbow positions. We divided 39 adolescent baseball players into two groups, 19 pitchers and 20 fielders, according to the amount of throwing. Twenty-four non-athlete junior high school students were also included as controls. We ultrasonographically examined each participant's ulnar nerve in the cubital tunnel with the elbow extended and at 45°, 90° and 120° of flexion. Anterior translation and flattening of the ulnar nerve occurred in all groups. Pitchers had larger-scale anterior translation than did controls. In pitchers, the ulnar nerve exhibited more anterior movement on the dominant side than on the non-dominant side. The anterior subluxation of the ulnar nerve occurred in players without ulnar nerve palsy and was not correlated with elbow pain. In addition to the known musculoskeletal adaptations of pitchers' elbows, ultrasonography revealed new changes in the ulnar nerve, anterior translation and subluxation, after repetitive throwing. These changes might also be physiologic adaptations of throwing elbows.