Why is the humeral retroversion of throwing athletes greater in dominant shoulders than in nondominant shoulders?

• DOI: 10.1016/j.jse.2005.06.009
• Publication Date: 2006-09-15T12:14:11Z
• Authors: Nobuyuki Yamamoto; Eiji Itoi; Hiroshi Minagawa; Masakazu Urayama; Hidetomo Saito; Nobutoshi Seki; Takenobu Iwase; Shinji Kashiwaguchi; Tetsuya Matsuura
• Keywords: Male; Time Factors; Adolescent; Shoulder Joint; Age Factors; Humerus; Baseball; Adaptation, Physiological; Biomechanical Phenomena; 03 medical and health sciences; 0302 clinical medicine; Athletic Injuries; Elbow Joint; Humans; Range of Motion, Articular; Shoulder Injuries; Child; Ultrasonography

A rotation angle of the proximal humerus relative to the elbow (bicipital-forearm angle) was measured by use of ultrasonography to determine the relationship between humeral retroversion and growth in dominant and nondominant shoulders of 66 elementary and junior high school baseball players. The subjects were aged 12 years on average. The bicipital-forearm angle was significantly smaller in dominant shoulders than in nondominant shoulders. This indicated that the retroversion angle was greater in dominant shoulders than in nondominant shoulders. Furthermore, there was a moderately positive correlation between age and the bicipital-forearm angle in both dominant and nondominant shoulders. From these data, we conclude that the humeral retroversion angle decreases with age, and the decrease is much smaller in dominant shoulders. We assume that the repetitive throwing motion does not increase the retroversion of the humeral head but rather restricts the physiologic derotation process of the humeral head during growth.