Poster 207: Chronic Adaptations of the Ulnar Nerve in Professional Baseball Pitchers

OBJECTIVES: The presence of ulnar neuropathy in baseball pitchers is a poor prognostic factor of successful return to play and may adversely impact outcomes after ulnar collateral ligament reconstruction (UCLR). Screening programs to identify negative ulnar nerve adaptations in throwing athletes can help minimize injury risk, individualize treatment programs, and optimize rehabilitation. Ultrasound provides the advantage of viewing structural adaptations prior to the onset of symptoms, an important factor in identifying potential injuries in advance. However, it is currently unclear how the ulnar nerve adapts chronically in professional baseball pitchers. Therefore, the primary purpose of this study was to compare ulnar nerve ultrasound characteristics between the throwing (dominant) and non- throwing control (non-dominant) elbows in professional pitchers, with a secondary purpose of comparing ultrasound characteristics between subluxing and non-subluxing ulnar nerves. The authors hypothesized that ulnar nerve area and echogenicity (i.e. brightness) would be increased in the throwing elbow. METHODS: All healthy professional baseball pitchers from a single organization underwent bilateral ultrasound examination at the beginning of the 2022 Minor League Baseball spring training. Ultrasound examination was done by a musculoskeletal radiologist (**) for imaging and subsequent quantification of the ulnar nerve properties, as well as to identify ulnar nerve subluxation. ImageJ software was utilized to measure ulnar nerve area, echogenicity (i.e. brightness), and circularity by one investigator (**) who was blinded to subluxation findings and arm dominance. Comparison of ulnar nerve ultrasound characteristics were performed between: dominant vs. non-dominant elbows, subluxing vs. non- subluxing dominant elbows, and between all (dominant and non-dominant) subluxing vs. non-subluxing elbows. RESULTS: Overall, 74 male professional baseball pitchers (age: 22.5 ± 2.4 years; professional experience: 1.7 ± 1.5 years) were enrolled. There was a trend toward statistical significance for echogenicity bilaterally (dominant: 137 optical density vs. non-dominant: 128 optical density, p=0.053), while area (0.2 mm(2) vs. 0.2 mm(2), p=0.767) and circularity (0.67 vs. 0.69, p=0.165) did not differ bilaterally (Table 1). There were no demographic differences between pitchers with subluxing vs. non-subluxing dominant ulnar nerves, including similar years of professional experience and similar Beighton hypermobility scores between groups (Table 2). Echogenicity was significantly lower in subluxing dominant ulnar nerves compared to non-subluxing dominant ulnar nerves (128 optical density vs. 142 optical density, p=0.020). Echogenicity remained significantly lower in subluxing ulnar nerves after evaluating all subluxing vs. non-subluxing elbows (121 optical density vs. 138 optical density, p=0.001) (Table 3). Ulnar nerve area and circularity did not differ based on ulnar nerve subluxation. CONCLUSIONS: There was a trend towards the ulnar nerve of the throwing elbow having increased echogenicity relative to the non-throwing elbow, suggesting that echogenicity may play a role in the chronic adaptations of the ulnar nerve. Nerve echogenicity also differed based on ulnar nerve subluxation, however further research is necessary to determine why this difference exists and the potential direction of causality.