title: The 2012 Otto Aufranc Award: The interpretation of metal ion levels in unilateral and bilateral hip resurfacing.
abstract: BACKGROUND
  The interpretation of metal ion concentrations and their role in clinical management of patients with metal-on-metal implants is still controversial.
  
  
  OBJECTIVE
  We questioned whether patients undergoing hip resurfacing with no clinical problems could be differentiated from those with clinical (pain, loss of function) and/or radiographic (component malpositioning, migration, bone loss), problems based on metal ion levels, and if there was a threshold metal level that predicted the need for clinical intervention. Furthermore, we asked if patient and implant factors differed between these functional groups.
  
  
  METHODS
  We retrospectively identified 453 unilateral and 139 bilateral patients with ion measurements at minimum followup of 12 months (mean, 4.3 years; range, 1-12.9 years). Patients were designated as well functioning or poorly functioning based on strict criteria. The acceptable upper levels within the well-functioning group were determined from the 75th percentile plus 1.5× interquartile range. The sensitivity and specificity of these levels to predict clinical problems were calculated.
  
  
  RESULTS
  Well-functioning group ions were lower than the poorly functioning group ion levels. The acceptable upper levels were: chromium (Cr) 4.6 μg/L, cobalt (Co) 4.0 μg/L unilateral and Cr 7.4 μg/L, Co 5.0 μg/L bilateral. The specificity of these levels in predicting poor function was high (95%) and sensitivity was low (25%). There were more males in the well-functioning group and more females and smaller femoral components in the poorly functioning group.
  
  
  CONCLUSIONS
  Metal levels higher than these proposed safe upper limits can predict problems with metal-on-metal resurfacings and are important parameters in the management of at-risk patients.
  
  
  METHODS
  Level II, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.
authors.affiliation: ANCA Medical Centre, Ghent, Belgium. cathvds@telenet.be
authors.forename: Catherine
authors.initials: C
authors.lastname: Van Der Straeten
authors.forename: George
authors.initials: G
authors.lastname: Grammatopoulos
authors.forename: Harinderjit S
authors.initials: HS
authors.lastname: Gill
authors.forename: Alessandro
authors.initials: A
authors.lastname: Calistri
authors.forename: Patricia
authors.initials: P
authors.lastname: Campbell
authors.forename: Koen A
authors.initials: KA
authors.lastname: De Smet
mesh_terms: D000328:Adult; D000368:Aged; D019644:Arthroplasty, Replacement, Hip; D001363:Awards and Prizes; D005260:Female; D005500:Follow-Up Studies; D006621:Hip Joint / Q000601:surgery*; D006622:Hip Prosthesis; D049674:History, 21st Century; D006801:Humans; D008297:Male; D008670:Metals; D008875:Middle Aged; D015207:Osteoarthritis, Hip / Q000601:surgery; D011474:Prosthesis Design; D011475:Prosthesis Failure; D012189:Retrospective Studies
chemical_list: D008670:Metals