title: The anterior deltoid's importance in reverse shoulder arthroplasty: a cadaveric biomechanical study.
abstract: BACKGROUND
  Frequently, patients who are candidates for reverse shoulder arthroplasty have had prior surgery that may compromise the anterior deltoid muscle. There have been conflicting reports on the necessity of the anterior deltoid thus it is unclear whether a dysfunctional anterior deltoid muscle is a contraindication to reverse shoulder arthroplasty. The purpose of this study was to determine the 3-dimensional (3D) moment arms for all 6 deltoid segments, and determine the biomechanical significance of the anterior deltoid before and after reverse shoulder arthroplasty.
  
  
  METHODS
  Eight cadaveric shoulders were evaluated with a 6-axis force/torque sensor to assess the direction of rotation and 3D moment arms for all 6 segments of the deltoid both before and after placement of a reverse shoulder prosthesis. The 2 segments of anterior deltoid were unloaded sequentially to determine their functional role.
  
  
  RESULTS
  The 3D moment arms of the deltoid were significantly altered by placement of the reverse shoulder prosthesis. The anterior and middle deltoid abduction moment arms significantly increased after placement of the reverse prosthesis (P < .05). Furthermore, the loss of the anterior deltoid resulted in a significant decrease in both abduction and flexion moments (P < .05).
  
  
  CONCLUSIONS
  The anterior deltoid is important biomechanically for balanced function after a reverse total shoulder arthroplasty. Losing 1 segment of the anterior deltoid may still allow abduction; however, losing both segments of the anterior deltoid may disrupt balanced abduction. Surgeons should be cautious about performing reverse shoulder arthroplasty in patients who do not have a functioning anterior deltoid muscle.
authors.affiliation: Department of Orthopaedic Surgery, Northwestern University, Chicago, IL, USA. daniel.g.schwartz@gmail.com
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Schwartz
authors.forename: Sang Hoon
authors.initials: SH
authors.lastname: Kang
authors.forename: T Sean
authors.initials: TS
authors.lastname: Lynch
authors.forename: Sara
authors.initials: S
authors.lastname: Edwards
authors.forename: Gordon
authors.initials: G
authors.lastname: Nuber
authors.forename: Li-Qun
authors.initials: LQ
authors.lastname: Zhang
authors.forename: Matthew
authors.initials: M
authors.lastname: Saltzman
mesh_terms: D000368:Aged; D019643:Arthroplasty, Replacement; D001696:Biomechanical Phenomena; D002102:Cadaver; D057645:Deltoid Muscle / Q000502:physiology*; D005260:Female; D006801:Humans; D007595:Joint Prosthesis; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D012399:Rotation; D012785:Shoulder Joint / Q000502:physiology* / Q000601:surgery*