title: Pseudotumors are common in well-positioned low-wearing metal-on-metal hips.
abstract: BACKGROUND
  Pseudotumors are sterile inflammatory lesions found in the soft tissues surrounding metal-on-metal (MOM) and metal-on-polyethylene hip arthroplasties. In patients with MOM hip arthroplasties, pseudotumors are thought to represent an adverse reaction to metal wear debris. However, the pathogenesis of these lesions remains unclear. Currently, there is inconsistent evidence regarding the influence of adverse cup position and increased wear in the formation of pseudotumors.
  
  
  OBJECTIVE
  We therefore determined whether pseudotumor formation was associated with (1) adverse cup position, (2) raised metal ion levels, and (3) increased wear rates of the retrieved components.
  
  
  METHODS
  We retrospectively reviewed all 352 patients for whom we had retrieved specimens from revisions of a current-generation MOM hip prosthesis between February 2008 and September 2010; of these, 105 met our inclusion criteria. We used multivariate logistic regression analysis to compare acetabular orientation, metal ion levels before revision, and component wear rates between patients with (n = 72) and without (n = 33) pseudotumors, according to findings on metal artifact reduction sequence MRI.
  
  
  RESULTS
  The proportion of patients demonstrating evidence of a pseudotumor in well-positioned hips was similar to those with adverse cup positions (67% and 66%, respectively). Patients revised with pseudotumors had similar whole-blood metal ion levels and component wear rates to those who were not revised.
  
  
  CONCLUSIONS
  Pseudotumors were not associated with increased wear or metal ion levels, suggesting patient susceptibility is likely to be more important.
authors.affiliation: Department of Musculoskeletal Surgery, Imperial College London, London, SW7 2AZ, UK. ashley.matthies09@imperial.ac.uk
authors.forename: Ashley K
authors.initials: AK
authors.lastname: Matthies
authors.forename: John A
authors.initials: JA
authors.lastname: Skinner
authors.forename: Humza
authors.initials: H
authors.lastname: Osmani
authors.forename: Johann
authors.initials: J
authors.lastname: Henckel
authors.forename: Alister J
authors.initials: AJ
authors.lastname: Hart
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000295:instrumentation*; D005260:Female; D006104:Granuloma, Plasma Cell / Q000209:etiology* / Q000473:pathology / Q000601:surgery; D006622:Hip Prosthesis; D006801:Humans; D016015:Logistic Models; D008131:London; D008279:Magnetic Resonance Imaging; D008297:Male; D008670:Metals / Q000097:blood; D008875:Middle Aged; D015999:Multivariate Analysis; D016017:Odds Ratio; D011474:Prosthesis Design; D012086:Reoperation; D012189:Retrospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D008670:Metals