title: Spontaneous dissociation of offset, face-changing polyethylene liners from the acetabular shell: a report of four cases.
abstract: BACKGROUND
  Dissociation of the polyethylene liner from the acetabular shell is an uncommon event. Offset, face-changing polyethylene liners theoretically increase femoral head coverage, allow for larger heads with smaller cup diameters, and offer improved stability without risk of impingement. However, we present four cases of liner dissociations from the acetabular shell that necessitated revision hip surgery.
  
  
  METHODS
  Four patients with spontaneous dissociations of offset, face-changing polyethylene acetabular liners underwent revision hip arthroplasty between January 2007 and June 2010. All patients were women with an average age of fifty-three years. All cases involved the combination of a Pinnacle acetabular component with an offset, face-changing polyethylene liner. We reviewed the presenting signs and symptoms associated with liner dissociations and analyzed the radiographs for the acetabular component position.
  
  
  RESULTS
  All cases of liner dissociation occurred without direct trauma and were associated with squeaking sounds reported by the patient. The average cup abduction angle was 55° (range, 51° to 60°) and the average anteversion was 21.5° (range, 17° to 24°). Examination of the dissociated liners at the time of revision surgery revealed plastic deformation of the polyethylene liner rim posterosuperiorly at the eleven o'clock position on the right hip and the one o'clock position on the left hip.
  
  
  CONCLUSIONS
  The combination of a vertically positioned acetabular component and an offset, face-changing liner resulted in impingement and dissociation of the liner from the shell in four patients. Proper acetabular component positioning, rather than the routine use of uniquely designed polyethylene liners, is critical to maximizing implant stability in total hip arthroplasty.
authors.affiliation: Penn Presbyterian Medical Center, Philadelphia, Pennsylvania, USA.
authors.forename: Chancellor F
authors.initials: CF
authors.lastname: Gray
authors.forename: Ryan E
authors.initials: RE
authors.lastname: Moore
authors.forename: Gwo-Chin
authors.initials: GC
authors.lastname: Lee
mesh_terms: D000328:Adult; D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects* / Q000295:instrumentation*; D005260:Female; D006622:Hip Prosthesis / Q000009:adverse effects*; D006801:Humans; D008875:Middle Aged; D015207:Osteoarthritis, Hip / Q000601:surgery*; D020959:Polyethylene; D011474:Prosthesis Design; D011475:Prosthesis Failure; D012086:Reoperation
chemical_list: D020959:Polyethylene