title: Influence of glenoid component design and humeral component retroversion on internal and external rotation in reverse shoulder arthroplasty: a cadaver study.
abstract: BACKGROUND
  A common disadvantage of reverse shoulder arthroplasty is limitation of the range of arm rotation. Several changes to the prosthesis design and implantation technique have been suggested to improve rotation range of motion (ROM).
  
  
  OBJECTIVE
  Glenoid component design and degree of humeral component retroversion influence rotation ROM after reverse shoulder arthroplasty.
  
  
  METHODS
  The Aequalis Reversed™ shoulder prosthesis (Tornier Inc., Edina, MN, USA) was implanted into 40 cadaver shoulders. Eight glenoid component combinations were tested, five with the 36-mm sphere (centred seating, eccentric seating, inferior tilt, centred with a 5-mm thick lateralised spacer, and centred with a 7-mm thick lateralised spacer) and three with the 42-mm sphere (centred with no spacer or with a 7-mm or 10-mm spacer). Humeral component position was evaluated with 0°, 10°, 20°, 30°, and 40° of retroversion. External and internal rotation ROMs to posterior and anterior impingement on the scapular neck were measured with the arm in 20° of abduction.
  
  
  RESULTS
  The large glenosphere (42 mm) was associated with significantly (P<0.05) greater rotation ROMs, particularly when combined with a lateralised spacer (46° internal and 66° external rotation). Rotation ROMs were smallest with the 36-mm sphere. Greater humeral component retroversion was associated with a decrease in internal rotation and a significant increase (P<0.05) in external rotation. The best balance between rotation ROMs was obtained with the native retroversion, which was estimated at 17.5° on average in this study.
  
  
  CONCLUSIONS
  Our anatomic study in a large number of cadavers involved a detailed and reproducible experimental protocol. However, we did not evaluate the variability in scapular anatomy. Earlier studies of the influence of technical parameters did not take humeral component retroversion into account. In addition, no previous studies assessed rotation ROMs.
  
  
  CONCLUSIONS
  Rotation ROM should be improved by the use of a large-diameter glenosphere with a spacer to lateralise the centre of rotation of the gleno-humeral joint, as well as by positioning the humeral component at the patient's native retroversion value.
authors.affiliation: Université François-Rabelais de Tours, Faculté de Médecine de Tours, CHRU Trousseau, Service d'orthopédie traumatologie 2A, 1C, avenue de la République, 37170 Chambray-les-Tours, France. Electronic address: julien.berhouet@gmail.com.
authors.forename: J
authors.initials: J
authors.lastname: Berhouet
authors.forename: P
authors.initials: P
authors.lastname: Garaud
authors.forename: L
authors.initials: L
authors.lastname: Favard
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019643:Arthroplasty, Replacement / Q000379:methods*; D001696:Biomechanical Phenomena; D060751:Bone Retroversion / Q000503:physiopathology; D002102:Cadaver; D005260:Female; D061165:Glenoid Cavity; D006801:Humans; D006811:Humerus; D007593:Joint Instability / Q000503:physiopathology; D007595:Joint Prosthesis; D008297:Male; D008875:Middle Aged; D011474:Prosthesis Design; D016059:Range of Motion, Articular / Q000502:physiology*; D012399:Rotation; D012785:Shoulder Joint / Q000503:physiopathology* / Q000601:surgery*
keywords: Glenoid component combinations; Humeral component retroversion; Reverse shoulder prosthesis; Rotations