title: Inter and intra-system size variability of reverse shoulder arthroplasty polyethylene inserts.
abstract: BACKGROUND
  As the incidence of reverse shoulder arthroplasty (RSA) increases, so will the revision burden. At times, the revision surgeon may be faced with a well-fixed component on one side of the joint and revision implants from a different manufacturer. The ability to use glenoid and humeral implants from different manufacturers could simplify the revision procedure. This study hypothesized that across a range of RSA systems, some implants would demonstrate high size compatibility and others would demonstrate low compatibility.
  
  
  METHODS
  Six polyethylene inserts each from eight reverse total shoulder arthroplasty systems were examined (48 total inserts). All inserts were scanned using a laboratory micro-computed tomography scanner at 50 μm isotropic voxel spacing, and their surface geometries were reconstructed. The different implant geometries were co-registered, and the three-dimensional (3D) variability between the articular surfaces of the different implant systems was measured. Intrasystem manufacturing variability was also determined by measuring the 3D variability of inserts from the same system.
  
  
  RESULTS
  The intersystem polyethylene articular surface deviations between same-size systems were not significantly different (P = 0.61) and were a mean maximum of 60 ± 16 μm (range: 30-80 μm). Intrasystem manufacturing variability was equivalent between all but two models, averaging 49 ± 17 μm (range: 23-99 μm).
  
  
  CONCLUSIONS
  Differences in articular geometry between same-size inserts from different systems were on the same scale as intrasystem manufacturing variability, suggesting that different implant systems of the same nominal diameter could potentially be used interchangeably in revision or extenuating circumstances.
  
  
  CONCLUSIONS
  The results of this study suggest that surgeons can theoretically interchange same-sized implant components from the different RSA systems tested when conducting revisions.
authors.affiliation: Department of Surgery, Robarts Research Institute, Western University, London, Ontario, Canada; Department of Medical Biophysics, Robarts Research Institute, Western University, London, Ontario, Canada; Department of Lawson Health Research Institute, Robarts Research Institute, Western University, London, Ontario, Canada.
authors.forename: Matthew G
authors.initials: MG
authors.lastname: Teeter
authors.affiliation: Imaging Research Laboratories, Robarts Research Institute, Western University, London, Ontario, Canada.
authors.forename: Matthew T
authors.initials: MT
authors.lastname: Dawson
authors.affiliation: Department of Surgery, Robarts Research Institute, Western University, London, Ontario, Canada; Department of Roth McFarlane Hand and Upper Limb Centre, St. Joseph's Health Care, London, Ontario, Canada.
authors.forename: George S
authors.initials: GS
authors.lastname: Athwal
keywords: Polyethylene; micro-computed tomography; reverse shoulder arthroplasty; revision; shoulder arthroplasty