title: Large fixed-size metal-on-metal total hip arthroplasty: higher serum metal ion levels in patients with pain.
abstract: OBJECTIVE
  Recently, concerns have arisen about metal-on-metal (MoM) total hip arthroplasty (THA). Therefore, the purpose of this cross-sectional cohort study was to describe the incidence of pain, pseudotumours, revisions and the relation between elevated metal ion levels, functional outcome and quality of life after MoM THA.
  
  
  METHODS
  In 351 patients, 377 MoM THA with a fixed-size 38-mm head were evaluated with a mean follow-up of 30 months (range 11-58). Evaluation included pain, serum metal ions, patient-reported questionnaires (Short Form-36 [SF-36], Hip disability and Osteoarthritis Outcome Score [HOOS] and the Oxford Hip Score [OHS]) and radiological imaging. Sixteen patients did not participate in the screening.
  
  
  RESULTS
  One hundred and eighteen (35 %) patients reported pain and showed significantly higher cobalt and chromium levels compared to patients without pain. Median serum cobalt levels were 4.4 μg/l (interquartile range [IQR] 6.6) and chromium levels were 3.6 μg/l (IQR 4.8). Patients with cobalt levels of ≤5 μg/l reported significantly better outcome on the SF-36 and HOOS. Fifty-seven pseudotumours were identified in 227 THAs. A revision rate of 19 % was observed.
  
  
  CONCLUSIONS
  In conclusion, 35 % of the patients experienced pain after MoM THA. These patients showed significantly higher serum metal ion levels. The patient-reported questionnaires indicated significantly better outcome in patients with cobalt levels ≤5 μg/l.
authors.affiliation: Department of Orthopaedics, Leiden University Medical Centre, Leiden, The Netherlands, c.smeekes@lumc.nl.
authors.forename: Christiaan
authors.initials: C
authors.lastname: Smeekes
authors.forename: Bastiaan
authors.initials: B
authors.lastname: Ongkiehong
authors.forename: Bart
authors.initials: B
authors.lastname: van der Wal
authors.forename: Ron
authors.initials: R
authors.lastname: Wolterbeek
authors.forename: Jan-Ferdinand
authors.initials: JF
authors.lastname: Henseler
authors.forename: Rob
authors.initials: R
authors.lastname: Nelissen
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000379:methods*; D002857:Chromium / Q000097:blood*; D003035:Cobalt / Q000097:blood*; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D005260:Female; D005500:Follow-Up Studies; D006104:Granuloma, Plasma Cell / Q000453:epidemiology / Q000209:etiology*; D006622:Hip Prosthesis / Q000009:adverse effects*; D006801:Humans; D015994:Incidence; D008297:Male; D008670:Metals / Q000097:blood* / Q000627:therapeutic use; D008875:Middle Aged; D010146:Pain / Q000453:epidemiology / Q000209:etiology*; D011474:Prosthesis Design; D011788:Quality of Life; D012086:Reoperation / Q000706:statistics & numerical data*; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires; D016896:Treatment Outcome
chemical_list: D008670:Metals; D002857:Chromium; D003035:Cobalt