Is the degree of carrying angle associated with ulnar nerve instability? A cross-sectional study of high school baseball pitchers

Yuhei Hatori; Tsuyoshi Tajika; Hitoshi Shitara; Koichiro Yanai; Ryosuke Negishi; Ryosuke Miyamoto; Takuma Kachi; Fukuhisa Ino; Tsuyoshi Sasaki; Noritaka Hamano; Masataka Kamiyama; Masaaki Sakamoto; Kenji Takagishi; Hirotaka Chikuda

doi:10.1016/j.xrrt.2026.100724

Is the degree of carrying angle associated with ulnar nerve instability? A cross-sectional study of high school baseball pitchers

JSES Rev Rep Tech. 2026 Mar 20;6(3):100724. doi: 10.1016/j.xrrt.2026.100724. eCollection 2026 Aug.

Affiliations

¹ Department of Orthopaedic Surgery, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan.
² Graduate School of Health Sciences, Gunma University, Maebashi, Gunma, Japan.
³ Department of Physical Therapy, Takasaki University of Health and Welfare, Takasaki, Gunma, Japan.
⁴ Department of Orthopaedic Surgery, Sada Hospital, Fukuoka, Fukuoka, Japan.

Abstract

Background: An increased carrying angle (CA) on the throwing side has been observed in professional pitchers. Elbow alignment is known to be a factor in the strain stress on the ulnar nerve. Ulnar nerve instability (UNI), in which the nerve snaps forward over the medial epicondyle during elbow flexion, is reportedly more common in pitchers than in other players. However, no studies have examined the association between elbow alignment and UNI severity in baseball players. This study assessed the correlation between the CA and UNI severity in high school baseball pitchers.

Methods: A total of 106 high school baseball pitchers who underwent medical checkups during the off-season in 2023 were examined. Ultrasound examinations were conducted to assess the presence or absence of UNI and medial joint space under rest and gravity stress on both sides of the elbow. The participants were divided into the following 3 groups based on the ultrasonographic findings of UNI: no instability (type N), subluxation (type S), and dislocation (type D). Clinical and physical examinations were performed, which included measurement of CA, grip strength, key pinch strength, and a check for ulnar nerve symptoms bilaterally.

Results: The distribution of UNI types on the throwing side was 37%, 31%, and 32% for types N, S, and D, respectively. A similar distribution was found on the nonthrowing side: 36% for Type N, 32% for Type S, and 32% for Type D. Overall, there was no statistically significant difference in the prevalence of these types between the 2 sides. The CA of the throwing arm did not differ significantly between the 3 UNI groups: Type N (13.6° ± 0.4°), Type S (12.7° ± 0.3°), and Type D (12.0° ± 0.3°) (P = .25). On the throwing side, the different UNI types did not show significant differences in the degree of ulnar collateral ligament laxity or in other clinical and physical findings.

Conclusion: This study found no significant difference in bony alignment, as indicated by the CA, between the degrees of UNI among high school baseball pitchers. When categorized by UNI type, no significant differences were observed in the throwing side with respect to ulnar collateral ligament laxity or other clinical and physical findings.

Keywords: Baseball; Carrying angle; Elbow; Instability; Pitcher; Ulnar collateral ligament; Ulnar nerve; Ulnohumeral joint.