Relationship Between Humeral Retroversion and Length of Baseball Career Before the Age of 16 Years

Abstract

Background: Humeral retroversion physiologically decreases during growth. However, in throwing athletes, the external forces caused by repetitive throwing are thought to increase humeral retroversion on the dominant side compared with that on the nondominant side. Purpose: To investigate the correlation between humeral retroversion and length of baseball career before age 16 years. Study Design: Cross-sectional study; Level of evidence, 3. Methods: A total of 112 high school baseball players (32 pitchers and 80 position players) with a mean age of 15.6 years (range, 15-16 years) were enrolled in the study. All participants completed questionnaires regarding their player position and the age when they started baseball and were given physical examinations. Shoulder range of motion and humeral retroversion were assessed on the dominant and nondominant sides. Humeral retroversion (rotation angle of the proximal humerus relative to the distal humerus) was measured ultrasonographically. Results: Humeral retroversion was significantly greater on the dominant side than on the nondominant side in both pitchers ( P < .0001) and position players ( P = .0005). The side-to-side difference in humeral retroversion in pitchers (13.9° ± 11.2°) was significantly greater than that in position players (9.0° ± 11.1°, P = .0361). In pitchers, there was a significant negative correlation between humeral retroversion and the age at which the players had started baseball ( P = .033, β = −2.494). Conclusion: These results suggest that humeral retroversion increases with decreasing age at commencement of a baseball career before age 16 years in pitchers.