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

Context: Screening programs to identify negative ulnar nerve adaptations in throwing athletes can help minimize injury risk and individualize treatment programs prior to the onset of symptoms. However, it is currently unclear how the ulnar nerve structurally adapts chronically in professional baseball pitchers. Objective: To compare ulnar nerve ultrasound structural characteristics between the throwing (dominant) and non-throwing control (non-dominant) elbows in professional pitchers, with a secondary purpose of comparing ultrasound structural characteristics between subluxating and non-subluxating ulnar nerves. Design: Cross-sectional study. Setting: The beginning of the 2022 Minor League Baseball spring training of a single professional baseball organization. Participants: All asymptomatic professional baseball pitchers from a single organization. Main Outcome Measures: Bilateral elbow ultrasound examinations by a musculoskeletal radiologist for subsequent image quantification of ulnar nerve properties (echogenicity, area, circularity), as well as to identify ulnar nerve subluxation. Results: Overall, 67 male professional baseball pitchers were enrolled. No significant bilateral differences in ulnar nerve cross-sectional area (dominant: 0.2 cm2 vs. non-dominant: 0.2 cm2, p=0.4), echogenicity (137 pixel intensity vs. 128 pixel intensity, p=0.07), or circularity (0.67 vs. 0.69, p=0.4) were observed. Ulnar nerve echogenicity was significantly lower in subluxating dominant ulnar nerves compared to non-subluxating dominant ulnar nerves (127 pixel intensity vs. 143 pixel intensity, p=0.006), while no significant differences in ulnar nerve area (0.2 mm2 vs. 0.2 mm2, p=0.1) or circularity (0.68 vs. 0.66, p=0.4) were observed between groups. Conclusions: The ulnar nerve of the throwing elbow had similar cross-sectional area, echogenicity, and circularity compared to the non-dominant ulnar nerve. Nerve echogenicity was significantly decreased in subluxating ulnar nerves, however further research is necessary to determine why this difference exists and the potential direction of causality.