Is ulnar nerve instability associated with medial elbow injury and dysesthesia in the ulnar nerve distribution in young baseball players?

To clarify the relationship between UNI and medial elbow injuries and dysesthesia in young baseball players. To clarify the relationship between UNI and medial elbow injuries and dysesthesia in young baseball players.

Ultrasonographic image of the ulnar nerve was obtained in 141 young baseball players (aged 9-15 years) in the following positions: 1) elbow extension position, 2) maximum elbow flexion position, and 3) shoulder in 90° abduction, maximum external rotation, and elbow maximum valgus position (maximum valgus position). UNI was defined as displacement of the ulnar nerve onto or anteriorly to the tip of the medial epicondyle in the elbow flexion or maximum valgus positions. The participants completed a questionnaire investigating their age, height, weight, elbow pain, and dysesthesia in the ulnar nerve distribution. Furthermore, the participants were divided into 2 groups according to their ultrasonographic abnormalities of the medial elbow joint. The presence or absence of UNI for the injury and noninjury groups were compared using a chi-square test. Additionally, in all participants, the relationship between the UNI and dysesthesia in the ulnar nerve distribution were examined using a Fisher exact test.

Of the 141 young baseball players, 64 (45.4 %; injury group) had ultrasonographic abnormalities of the medial elbow joint. In the injury group, 17 (26.6%) had UNI in the maximum flexion position and 11 (17.2%) had UNI in the maximum valgus position. In the noninjury group, 21 (27.3%) had UNI in the maximum flexion position, and 7 (9.1%) had UNI in the maximum valgus position. No significant difference was found in the flexion position (P = 1) and maximum valgus position (P = 0.238) between the 2 groups. Of the participants with UNI in the maximum flexion and maximum valgus positions, 3/38 (7.9%) and 3/18 (16.7%) had dysesthesia in the ulnar nerve distribution. There was no significant association between UNI and the medial elbow dysesthesia (P = 0.387) in the flexion position. However, in the maximum valgus position, there was a significant association between UNI and the dysesthesia (P = 0.045).

UNI was not associated with medial elbow injuries in young baseball players. Moreover, there was no significant association between UNI in the flexion position and dysesthesia in the ulnar nerve distribution. However, young baseball players with UNI in the maximum valgus position had dysesthesia in the ulnar nerve distribution.

Dysesthesia in the ulnar nerve distribution may be due to instability in the maximum valgus position during pitching. Therefore, evaluation of the UNI in maximum valgus position may be useful when identifying young baseball players at risk for sustaining dysesthesia in the ulnar nerve distribution.