title: Effect of humeral component version on impingement in reverse total shoulder arthroplasty.
abstract: OBJECTIVE
  Reverse shoulder arthroplasty is growing in popularity for patients with deficient rotator cuffs; however, the phenomenon of scapular notching continues to be a concern. This study examined the effects of humeral component version in the Aequalis Reversed Shoulder Prosthesis (Tornier, Edina, MN) on impingement of the humeral prosthesis against the scapula to test the hypothesis that the mechanical contact of the humeral component with the scapular neck is influenced by the version of the humeral component.
  
  
  METHODS
  Seven shoulders from deceased donors were tested after the Aequalis Reversed Shoulder was implanted. The deltoid, pectoralis major, and latissimus dorsi were loaded based on physiologic cross-sectional area. The degree of internal and external rotation when impingement, subluxation, or dislocation occurred was measured at 0°, 30°, and 60° glenohumeral abduction in the scapular plane. Testing was performed with the humeral component placed in 20° of anteversion, neutral version, 20° of retroversion, and 40° of retroversion.
  
  
  RESULTS
  Maximum external rotation at 0° abduction was -1° ± 4° at 20° anteversion, 15° ± 3° at neutral, 28° ± 4° at 20° retroversion, and 44° ± 5° at 40° retroversion (P < .05). Maximum internal rotation at 0° abduction was 128° ± 9° at 20° anteversion, 112° ± 9° at neutral, 99° ± 8° at 20° retroversion, and 83° ± 8° at 40° retroversion (P < .05). Maximum external rotation at 30° abduction was 70° ± 6° at 20° anteversion, 84° ± 7° at neutral, 97° ± 6° at 20° retroversion, and 110° ± 5° at 40° retroversion (P < .05). There was no limitation to internal rotation at 30° abduction. No impingement occurred at 60° abduction.
  
  
  CONCLUSIONS
  Version of the humeral component plays a role in range of motion and impingement in reverse total shoulder arthroplasty. Anteversion can significantly decrease the amount of external rotation achievable after reverse total shoulder surgery.
  
  
  CONCLUSIONS
  Placing the Aequalis Reversed Shoulder humeral component at between 20° and 40° of retroversion more closely restores a functional arc of motion without impingement.
authors.affiliation: University of Southern California Department of Orthopaedic Surgery, Los Angeles, CA, USA.
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Stephenson
authors.forename: Joo Han
authors.initials: JH
authors.lastname: Oh
authors.forename: Michelle H
authors.initials: MH
authors.lastname: McGarry
authors.forename: George F
authors.initials: GF
authors.lastname: Rick Hatch
authors.forename: Thay Q
authors.initials: TQ
authors.lastname: Lee
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019643:Arthroplasty, Replacement / Q000009:adverse effects / Q000379:methods*; D005260:Female; D006801:Humans; D006811:Humerus / Q000503:physiopathology*; D007595:Joint Prosthesis; D008297:Male; D008422:Materials Testing; D008875:Middle Aged; D011183:Postoperative Complications / Q000517:prevention & control; D016059:Range of Motion, Articular; D012399:Rotation; D012540:Scapula / Q000473:pathology; D019534:Shoulder Impingement Syndrome / Q000209:etiology / Q000503:physiopathology* / Q000517:prevention & control; D012785:Shoulder Joint / Q000503:physiopathology* / Q000601:surgery*; D013314:Stress, Mechanical