title: Humeral Retrotorsion and Glenohumeral Motion in Youth Baseball Players Compared With Age-Matched Nonthrowing Athletes.
abstract: BACKGROUND
  Baseball players exhibit a more posteriorly oriented humeral head in their throwing arm. This is termed humeral retrotorsion (HRT) and likely represents a response to the stress of throwing. This adaptation is thought to occur while the athlete is skeletally immature, however currently there is limited research detailing how throwing activity in younger players influences the development of HRT. In addition, it is presently unclear how this changing osseous orientation may influence shoulder motion within young athletes.
  
  
  OBJECTIVE
  To determine the influence of throwing activity and age on the development of side-to-side asymmetry in HRT and shoulder range of motion (ROM).
  
  
  METHODS
  Cross-sectional study; Level of evidence, 3.
  
  
  METHODS
  Healthy athletes (age range, 8-14 years) were categorized into 2 groups based upon sports participation; throwers (n = 85) and nonthrowers (n = 68). Bilateral measurements of HRT, shoulder external rotation (ER), internal rotation (IR), and total range of motion (TROM) at 90° were performed using diagnostic ultrasound and a digital inclinometer. Side-to-side asymmetry (dominant minus nondominant side) in HRT and in shoulder ER, IR, and TROM were assessed. Statistical analysis was performed with 2-way analysis of variance and Pearson correlation coefficients.
  
  
  RESULTS
  Throwers demonstrated a larger degree of HRT on the dominant side, resulting in greater asymmetry compared with nonthrowers (8.7° vs 4.8°). Throwers demonstrated a gain of ER (5.1°), a loss of IR (6.0°), and no change in TROM when compared with the nondominant shoulder. Pairwise comparisons identified altered HRT and shoulder ROM in all age groups, including the youngest throwers (age range, 8-10.5 years). A positive correlation existed between HRT and ER ROM that was stronger in nonthrowers ( r = 0.63) than in throwers ( r = 0.23), while a negative correlation existed with IR that was stronger in throwers ( r = -0.40) than in nonthrowers ( r = -0.27).
  
  
  CONCLUSIONS
  Throwing activity causes adaptive changes in HRT and shoulder ROM in youth baseball players at an early age. Other factors in addition to HRT influence shoulder motion within this population.
authors.affiliation: Sports Medicine and Performance Center at The Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA.|Department of Physical Therapy, Arcadia University, Glenside, Pennsylvania, USA.
authors.forename: Elliot M
authors.initials: EM
authors.lastname: Greenberg
authors.affiliation: Division of Orthopaedic Surgery, The Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA.|Department of Orthopaedic Surgery, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: J Todd R
authors.initials: JT
authors.lastname: Lawrence
authors.affiliation: Department of Physical Therapy, Nova Southeastern University, Fort Lauderdale, Florida, USA.
authors.forename: Alicia
authors.initials: A
authors.lastname: Fernandez-Fernandez
authors.affiliation: Department of Physical Therapy, Arcadia University, Glenside, Pennsylvania, USA.
authors.forename: Philip
authors.initials: P
authors.lastname: McClure
mesh_terms: D000293:Adolescent; D000367:Age Factors; D001484:Baseball; D060751:Bone Retroversion / Q000000981:diagnostic imaging / Q000209:etiology / Q000473:pathology*; D002648:Child; D003430:Cross-Sectional Studies; D006801:Humans; D058430:Humeral Head / Q000000981:diagnostic imaging / Q000473:pathology*; D008297:Male; D010414:Pennsylvania; D016059:Range of Motion, Articular; D012399:Rotation; D012782:Shoulder / Q000000981:diagnostic imaging / Q000502:physiology; D012785:Shoulder Joint / Q000000981:diagnostic imaging / Q000502:physiology*
keywords: baseball; humeral retrotorsion; injury prevention; shoulder range of motion