title: Why is the humeral retroversion of throwing athletes greater in dominant shoulders than in nondominant shoulders?
abstract: 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.
authors.affiliation: Division of Orthopedic Surgery, Department of Neuro and Locomotor Science, Akita University School of Medicine, Akita, Japan.
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Yamamoto
authors.forename: Eiji
authors.initials: E
authors.lastname: Itoi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Minagawa
authors.forename: Masakazu
authors.initials: M
authors.lastname: Urayama
authors.forename: Hidetomo
authors.initials: H
authors.lastname: Saito
authors.forename: Nobutoshi
authors.initials: N
authors.lastname: Seki
authors.forename: Takenobu
authors.initials: T
authors.lastname: Iwase
authors.forename: Shinji
authors.initials: S
authors.lastname: Kashiwaguchi
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Matsuura
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000293:Adolescent; D000367:Age Factors; D001265:Athletic Injuries / Q000503:physiopathology; D001484:Baseball / Q000293:injuries*; D001696:Biomechanical Phenomena; D002648:Child; D004551:Elbow Joint; D006801:Humans; D006811:Humerus / Q000000981:diagnostic imaging; D008297:Male; D016059:Range of Motion, Articular / Q000502:physiology*; D000070599:Shoulder Injuries; D012785:Shoulder Joint / Q000000981:diagnostic imaging / Q000503:physiopathology*; D013997:Time Factors; D014463:Ultrasonography