title: Effects of tilt and glenosphere eccentricity on baseplate/bone interface forces in a computational model, validated by a mechanical model, of reverse shoulder arthroplasty.
abstract: OBJECTIVE
  Reverse shoulder arthroplasty is being used with greater frequency for patients with severe rotator cuff deficiency. There are several commercially available reverse shoulder devices, each with different glenosphere options. The purpose of this study was to determine: (1) forces at the baseplate-bone interface in glenospheres with centers of rotation located concentrically and eccentrically to the center of the baseplate; and (2) if baseplate-bone forces can be optimized by altering tilt of the baseplate.
  
  
  METHODS
  A validated computer model was used to compare concentric glenospheres with neutral offset to eccentrically offset glenospheres (6 mm inferior or 6 mm lateral) in 3 baseplate tilts: 15° inferior, neutral, or 15° superior. A baseplate, simulated bone, screws, and humeral component were modeled, and forces underneath the baseplate were calculated as the arm was abducted through 90° of glenohumeral motion.
  
  
  RESULTS
  For lateral and concentric glenospheres, inferior tilt provides the most even distribution of forces (mean difference in force between superior and inferior portions of baseplate: 11.3 N and 24.7 N, respectively) and superior tilt provides the most uneven distribution of forces (109.3 N and 78.7 N, respectively). For inferior eccentric glenospheres, inferior tilt provides the most uneven distribution of forces (58.7 N) and neutral tilt provides the most even distribution of forces (27.7 N).
  
  
  CONCLUSIONS
  This is the first study to investigate force distribution under the baseplate in inferior eccentric glenospheres. Although inferior tilting of the baseplate is recommended for concentric and laterally offset glenospheres, this same recommendation may be detrimental to inferiorly offset glenospheres and warrants further investigation.
authors.affiliation: The Phillip Spiegel Orthopaedic Research Laboratory at the Foundation for Orthopaedic Research and Education, Tampa, FL, USA.
authors.forename: Sergio
authors.initials: S
authors.lastname: Gutiérrez
authors.forename: Matthew
authors.initials: M
authors.lastname: Walker
authors.forename: Matthew
authors.initials: M
authors.lastname: Willis
authors.forename: Derek R
authors.initials: DR
authors.lastname: Pupello
authors.forename: Mark A
authors.initials: MA
authors.lastname: Frankle
mesh_terms: D019643:Arthroplasty, Replacement / Q000295:instrumentation*; D001696:Biomechanical Phenomena; D003198:Computer Simulation; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology / Q000601:surgery*; D007595:Joint Prosthesis; D011474:Prosthesis Design; D016059:Range of Motion, Articular; D012785:Shoulder Joint / Q000503:physiopathology / Q000601:surgery*