title: Evaluation of the role of glenosphere design and humeral component retroversion in avoiding scapular notching during reverse shoulder arthroplasty.
abstract: BACKGROUND
  Scapular notching is a common observation during radiological follow-up of reverse shoulder arthroplasty. The purpose of this study was to evaluate the effect of glenosphere design and humeral component retroversion on movement amplitude in the scapular plane and inferior scapular impingement.
  
  
  METHODS
  The Aequalis Reversed Shoulder Prosthesis (Tornier) was implanted into 40 cadaver shoulders. On the glenoid side, 8 different combinations were tested: 36-mm glenosphere: centered (standard), eccentric, with an inferior tilt, or with the center of rotation (COR) lateralized by 5 or 7 mm; and 42-mm centered glenosphere: used alone or with the COR lateralized by 7 or 10 mm. The humeral component was positioned in 0°, 10°, 20°, 30°, and 40° of retroversion. Maximum adduction and abduction were measured when inferior impingement and superior impingement, respectively, were detected.
  
  
  RESULTS
  The average increase in abduction amplitude was 10° and inferior impingement occurred 18° later with a 42-mm glenosphere, especially when it was lateralized by 10 mm, relative to a 36-mm centered glenosphere (P < .05). These 2 combinations provided a 28° increase in the movement amplitude in the scapular plane. Positioning of the humeral component in 10° or 20° of retroversion or in anatomical retroversion was most effective at avoiding inferior impingement but had less effect on abduction range of motion (except with the 42-mm glenosphere).
  
  
  CONCLUSIONS
  Our study confirmed published results with various glenosphere designs but was unique in describing the effect of humeral retroversion on scapular impingement. Inferior scapular notching can be most effectively prevented by using large-diameter glenospheres with lateralized COR and by making sure to replicate the patient's native humeral retroversion.
authors.affiliation: François Rabelais University, Trousseau Hospital, Tours University Hospital Center, Orthopaedics and Trauma Department, Chambray-les-Tours, France. Electronic address: julien.berhouet@gmail.com.
authors.forename: Julien
authors.initials: J
authors.lastname: Berhouet
authors.affiliation: François Rabelais University, Trousseau Hospital, Tours University Hospital Center, Orthopaedics and Trauma Department, Chambray-les-Tours, France.
authors.forename: Pascal
authors.initials: P
authors.lastname: Garaud
authors.affiliation: François Rabelais University, Trousseau Hospital, Tours University Hospital Center, Orthopaedics and Trauma Department, Chambray-les-Tours, France.
authors.forename: Luc
authors.initials: L
authors.lastname: Favard
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019643:Arthroplasty, Replacement / Q000295:instrumentation / Q000379:methods*; D002102:Cadaver; D005260:Female; D006801:Humans; D006811:Humerus / Q000601:surgery*; D007595:Joint Prosthesis; D008297:Male; D008875:Middle Aged; D011474:Prosthesis Design; D011859:Radiography; D016059:Range of Motion, Articular; D012540:Scapula / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D012782:Shoulder / Q000601:surgery; D012785:Shoulder Joint / Q000601:surgery*
keywords: Basic Science Study; Biomechanics; Cadaver Model; Reverse shoulder arthroplasty; glenoid modularity; humeral version; scapular notching