title: Differences in humeral retroversion in dominant and nondominant sides of young baseball players.
abstract: BACKGROUND
  The relationship between the disabled throwing shoulder and humeral retroversion has recently attracted a great deal of attention. However, none of the previous studies clarified when the side-to-side difference of humeral retroversion in young baseball players would start. This study aimed to clarify when the difference of humeral retroversion in the dominant and nondominant sides appeared in baseball players.
  
  
  METHODS
  The bicipital-forearm angle in bilateral shoulders of 172 elementary school baseball players was measured by ultrasound. The bicipital-forearm angle was defined as an angle between the perpendicular line to the bicipital groove and the ulnar long axis with the elbow flexed at 90°. The correlation between the bicipital-forearm angle and the grade and the difference of the bicipital-forearm angle between the dominant and nondominant sides were analyzed.
  
  
  RESULTS
  In the nondominant shoulders, the bicipital-forearm angle increased with the grade in school (r = 0.32, P < .0001), but this was not observed in the dominant shoulders. In the fourth to sixth graders, the bicipital-forearm angles were significantly smaller in the dominant shoulders than in the nondominant shoulders.
  
  
  CONCLUSIONS
  Our findings indicated that humeral retroversion decreased with age in the nonthrowing side but not in the throwing side and that the side-to-side difference of humeral retroversion in the baseball players became obvious from the fourth grade. We assume that the repetitive throwing motion restricts the physiologic humeral derotation process and the difference became apparent from the fourth grade when the growth spurt begins in boys.
authors.affiliation: Department of Sports Medicine and Orthopaedic Surgery, Tohoku Rosai Hospital, Sendai, Japan; Department of Orthopaedic Surgery, Tohoku University School of Medicine, Sendai, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Kurokawa
authors.affiliation: Department of Orthopaedic Surgery, Tohoku University School of Medicine, Sendai, Japan.
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Yamamoto
authors.affiliation: Department of Physical Medicine and Rehabilitation, Tohoku University School of Medicine, Sendai, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Ishikawa
authors.affiliation: Department of Orthopaedic Surgery, Kurihara Central Hospital, Kurihara, Miyagi, Japan.
authors.forename: Hideaki
authors.initials: H
authors.lastname: Nagamoto
authors.affiliation: Department of Orthopaedic Surgery, Kesen-numa City Hospital, Kesen-numa, Miyagi, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Takahashi
authors.affiliation: Department of Orthopaedic Surgery, Kurihara Central Hospital, Kurihara, Miyagi, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Muraki
authors.affiliation: Department of Sports Medicine and Orthopaedic Surgery, Tohoku Rosai Hospital, Sendai, Japan.
authors.forename: Minoru
authors.initials: M
authors.lastname: Tanaka
authors.affiliation: Department of Sports Medicine and Orthopaedic Surgery, Tohoku Rosai Hospital, Sendai, Japan.
authors.forename: Katsumi
authors.initials: K
authors.lastname: Sato
authors.affiliation: Department of Orthopaedic Surgery, Tohoku University School of Medicine, Sendai, Japan. Electronic address: itoi-eiji@med.tohoku.ac.jp.
authors.forename: Eiji
authors.initials: E
authors.lastname: Itoi
mesh_terms: D000293:Adolescent; D001484:Baseball / Q000502:physiology*; D016022:Case-Control Studies; D002648:Child; D006801:Humans; D006811:Humerus / Q000000981:diagnostic imaging*; D008297:Male; D016059:Range of Motion, Articular / Q000502:physiology*; D012189:Retrospective Studies; D012574:Schools; D012785:Shoulder Joint / Q000000981:diagnostic imaging / Q000502:physiology*; D014463:Ultrasonography
keywords: Humeral retroversion; Little League shoulder; baseball player; growth period; throwing athlete; ultrasonography