title: Instability after reverse total shoulder replacement.
abstract: BACKGROUND
  Despite advances in technique and implant design, instability after reverse total shoulder arthroplasty remains a challenging postoperative complication.
  
  
  METHODS
  We examined our institutions' first 57 reverse total shoulder arthroplasties performed during a 3-year period (2004-2006). There were 9 cases of instability, all occurring within the first 6 months after surgery.
  
  
  RESULTS
  All 9 patients had compromise of the subscapularis tendon at the time of initial reverse total shoulder implantation. With regard to implant positioning, 2 patients had superiorly inclined metaglenes and 3 had metaglenes positioned superior to the inferior glenoid. Each patient with a dislocation had at least 1 revision surgery, and 4 patients had underlying infection. At most recent follow-up, only 3 patients had a concentrically reduced reverse total shoulder arthroplasty in place whereas 3 remained explanted, 2 chronically dislocated, and 1 chronically subluxated.
  
  
  CONCLUSIONS
  Early instability after reverse total shoulder arthroplasty can be related to inadequate soft tissue, inadequate deltoid tension, malpositioned implants, and/or infection, and outcomes of treatment of early instability are generally poor.
authors.affiliation: Bone and Joint Institute, Milton S. Hershey Medical Center, Pennsylvania State University College of Medicine, Hershey, PA, USA.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Gallo
authors.forename: Seth C
authors.initials: SC
authors.lastname: Gamradt
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Mattern
authors.forename: Frank A
authors.initials: FA
authors.lastname: Cordasco
authors.forename: Edward V
authors.initials: EV
authors.lastname: Craig
authors.forename: David M
authors.initials: DM
authors.lastname: Dines
authors.forename: Russell F
authors.initials: RF
authors.lastname: Warren
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019643:Arthroplasty, Replacement / Q000009:adverse effects* / Q000379:methods*; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000209:etiology*; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012785:Shoulder Joint / Q000601:surgery*; D016896:Treatment Outcome