title: Wear simulation of reverse total shoulder arthroplasty systems: effect of glenosphere design.
abstract: BACKGROUND
  Although early results with reverse total shoulder arthroplasty (rTSA) have been promising, concern exists about the high reported rates of scapular notching and the potential for catastrophic failure of glenoid component fixation. Generation of polyethylene wear debris may also contribute to notching and osteolysis of the scapula. A testing model for polyethylene wear is currently unavailable for reverse shoulder prostheses. The goal of this study was to develop a testing protocol using a commercially available hip simulator. Component design may also influence the generation of polyethylene debris. It is hypothesized that increased polyethylene wear occurs in glenospheres with holes in the articulating surface.
  
  
  METHODS
  Custom fixtures were fabricated to simulate both glenohumeral abduction and flexion on a 12-station hip wear simulator. Loading profiles for both abduction and flexion were alternated every 250,000 cycles for a total of 5 million cycles. Gravimetric analysis of humeral cups throughout the test was used to characterize wear. Lubricant fluid was collected throughout the test and digested for polyethylene particle analysis.
  
  
  RESULTS
  Comparisons of volumetric wear rates and total volume loss between glenospheres with and without holes and between flexion and abduction loading profiles showed similar results. Particle analysis displayed fibrillar particles with an equivalent circle diameter of 0.3 ± .1 μm and an aspect ratio of 2.5 ± 1.4.
  
  
  CONCLUSIONS
  This study represents the first wear simulation and particle characterization of reverse shoulder systems. No significant difference in wear was reported between glenospheres with and without holes.
authors.affiliation: Department of Orthopaedic Surgery, Beaumont Health System, Royal Oak, MI 48073, USA.
authors.forename: Zachary M
authors.initials: ZM
authors.lastname: Vaupel
authors.forename: Kevin C
authors.initials: KC
authors.lastname: Baker
authors.forename: Michael D
authors.initials: MD
authors.lastname: Kurdziel
authors.forename: J Michael
authors.initials: JM
authors.lastname: Wiater
mesh_terms: D019643:Arthroplasty, Replacement / Q000379:methods*; D019544:Equipment Failure Analysis; D006801:Humans; D007595:Joint Prosthesis; D008422:Materials Testing / Q000379:methods*; D011474:Prosthesis Design; D011475:Prosthesis Failure; D016059:Range of Motion, Articular; D012785:Shoulder Joint / Q000601:surgery*