title: Glenosphere dissociation after reverse shoulder arthroplasty.
abstract: BACKGROUND
  Reverse shoulder arthroplasty (RSA) is gaining popularity for the treatment of debilitating shoulder disorders. Despite marked improvements in patient satisfaction and function, the RSA complication rate is high. Glenosphere dissociation has been reported and may result from multiple mechanisms. However, few RSA retrieval studies exist.
  
  
  METHODS
  We reviewed our RSA database and identified patients with glenosphere dissociation between 1999 and 2013. Prosthesis type, glenosphere size, and contributing factors to dissociation were noted. Five retrieved implants were available for analysis, and evidence of wear or corrosion on the Morse taper was documented. Further, we biomechanically investigated improper Morse taper engagement that may occur intraoperatively as a potential cause of acute dissociation.
  
  
  RESULTS
  Thirteen patients with glenosphere dissociation were identified (0.5 months to 7 years postoperatively). Glenosphere size distribution was as follows: 32 mm (n = 1), 36 mm (n = 4), 40 mm (n = 6), and 44 mm (n = 2). Incidence of dissociation was correlated to glenosphere size (P < .001). Taper damage was limited to fretting wear, and there was minimal evidence of taper corrosion. Biomechanically, improper taper engagement reduced the torsional capacity of the glenosphere-baseplate interface by 60% from 19.2 ± 1.0 N-m to 7.5 ± 1.5 N-m.
  
  
  CONCLUSIONS
  We identified several mechanisms contributing to glenosphere dissociation after RSA, including trauma and improper taper engagement. Limited evidence of corrosive wear on the taper interface was identified. Although it is rare, the incidence of glenosphere dissociation was higher when 40- and 44-mm glenospheres were implanted compared with smaller glenospheres (32 and 36 mm), probably because of the larger exposed surface area for potential impingement.
authors: Florida Orthopaedic Institute, Shoulder and Elbow Service, Tampa, FL, USA.
authors: Michael C
authors: MC
authors: Cusick
authors: Florida Orthopaedic Institute, Shoulder and Elbow Service, Tampa, FL, USA.
authors: Michael M
authors: MM
authors: Hussey
authors: Florida Orthopaedic Institute, Shoulder and Elbow Service, Tampa, FL, USA.
authors: Brandon M
authors: BM
authors: Steen
authors: Florida Orthopaedic Institute, Shoulder and Elbow Service, Tampa, FL, USA.
authors: Robert U
authors: RU
authors: Hartzler
authors: Foundation for Orthopaedic Research and Education, Phillip Spiegel Orthopaedic Research Laboratory, Tampa, FL, USA.
authors: Rachel E
authors: RE
authors: Clark
authors: Suncoast Orthopaedic Surgery & Sports Medicine, Venice, FL, USA.
authors: Derek J
authors: DJ
authors: Cuff
authors: Foundation for Orthopaedic Research and Education, Phillip Spiegel Orthopaedic Research Laboratory, Tampa, FL, USA.
authors: Andres F
authors: AF
authors: Cabezas
authors: Foundation for Orthopaedic Research and Education, Phillip Spiegel Orthopaedic Research Laboratory, Tampa, FL, USA.
authors: Brandon G
authors: BG
authors: Santoni
authors: Florida Orthopaedic Institute, Shoulder and Elbow Service, Tampa, FL, USA. Electronic address: mfrankle@floridaortho.com.
authors: Mark A
authors: MA
authors: Frankle
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019643:Arthroplasty, Replacement / Q000009:adverse effects*; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D007592:Joint Diseases / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D011474:Prosthesis Design; D012189:Retrospective Studies; D012785:Shoulder Joint / Q000503:physiopathology / Q000601:surgery*
keywords: Morse taper; Reverse shoulder arthroplasty; dissociation