title: Effect of posterior shoulder tightness on internal impingement in a cadaveric model of throwing.
abstract: OBJECTIVE
  Posterior shoulder tightness is common in throwing athletes, especially those with symptomatic shoulder internal impingement. The role of posteroinferior capsular contracture in the pathoetiologies of throwing-related injuries caused by shoulder internal impingement remains unclear. The purpose of this study was to assess effect of posterior shoulder tightness on internal impingement in a cadaveric model of throwing.
  
  
  METHODS
  Seven fresh-frozen cadaveric shoulders were tested with the shoulder abducted to 90° and at maximum external rotation to simulate the late cocking phase of throwing motion. Glenohumeral joint contact pressure and area through internal impingement, humeral head shift, and the maximum humeral rotation angle were measured. Posteroinferior capsular plication was performed to simulate posteroinferior capsular tightness and induce glenohumeral internal rotation deficit.
  
  
  RESULTS
  Following generation of simulated posteroinferior capsular tightness with resultant glenohumeral internal rotation deficit, glenohumeral contact pressure was significantly increased (P < 0.05), the impinged area of rotator cuff tendon was significantly decreased (P < 0.05), and the humeral head shifted posteriorly (P < 0.05) during shoulder internal impingement.
  
  
  CONCLUSIONS
  Excessive posteroinferior capsular tightness can cause forceful internal impingement of the shoulder at maximum external rotation position.
authors: Department of Orthopedic Surgery, Osaka Medical College, 2-7 Daigaku-machi, Takatsuki, Osaka, 569-8686, Japan, tmihata@yahoo.co.jp.
authors: Teruhisa
authors: T
authors: Mihata
authors: Jeffrey
authors: J
authors: Gates
authors: Michelle H
authors: MH
authors: McGarry
authors: Masashi
authors: M
authors: Neo
authors: Thay Q
authors: TQ
authors: Lee
mesh_terms: D001265:Athletic Injuries / Q000503:physiopathology; D001696:Biomechanical Phenomena; D002102:Cadaver; D003286:Contracture / Q000503:physiopathology*; D005260:Female; D006801:Humans; D058430:Humeral Head / Q000503:physiopathology; D017746:Joint Capsule / Q000503:physiopathology; D007593:Joint Instability / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D008953:Models, Anatomic; D011312:Pressure; D016059:Range of Motion, Articular; D012399:Rotation; D019534:Shoulder Impingement Syndrome / Q000503:physiopathology*; D000070599:Shoulder Injuries; D012785:Shoulder Joint / Q000503:physiopathology*