title: Do ion levels in hip resurfacing differ from metal-on-metal THA at midterm?
abstract: BACKGROUND
  Metal-on-metal Birmingham hip resurfacing (MOM-BHR) is an alternative to metal-on-metal total hip arthroplasty (MOM-THA), especially for young and/or active patients. However, wear resulting in increased serum ion levels is a concern.
  
  
  OBJECTIVE
  We asked whether (1) serum chromium (Cr), cobalt (Co), and molybdenum (Mo) concentrations would differ between patients with either MOM-BHR or MOM-THA at 5 years, (2) confounding factors such as gender would influence ion levels; and (3) ion levels would differ at 2 and 5 years for each implant type.
  
  
  METHODS
  Ions were measured in two groups with either MOM-BHR (n = 20) or MOM-THA (n = 35) and a mean 5-year followup, and two groups with either MOM-BHR (n = 15) or MOM-THA (n = 25) and a mean 2-year followup. Forty-eight healthy blood donors were recruited for reference values.
  
  
  RESULTS
  At 5 years, there were no differences in ion levels between patients with MOM-BHR or MOM-THA. Gender was a confounding factor, and in the MOM-BHR group at 5 years, Cr concentrations were greater in females compared with those of males. Mean ion levels were similar in patients with 2 and 5 years of followup for each implant type. Ion levels in patients were sevenfold to 10-fold higher than in controls.
  
  
  CONCLUSIONS
  As the metal ion concentrations in the serum at 5 years were in the range reported in the literature, we do not believe concerns regarding excessive metal ion levels after MOM-BHR are justified.
  
  
  METHODS
  Level III, therapeutic study. See the Guidelines for Authors for a complete description of level of evidence.
authors.affiliation: Department II of Orthopaedics and Traumatology, Bologna University, Rizzoli Orthopaedic Institute, Via G C Pupilli 1, 40136 Bologna, Italy. a.moroni@ior.it
authors.forename: A
authors.initials: A
authors.lastname: Moroni
authors.forename: L
authors.initials: L
authors.lastname: Savarino
authors.forename: M
authors.initials: M
authors.lastname: Hoque
authors.forename: M
authors.initials: M
authors.lastname: Cadossi
authors.forename: N
authors.initials: N
authors.lastname: Baldini
mesh_terms: D000328:Adult; D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000295:instrumentation* / Q000379:methods; D002857:Chromium / Q000097:blood; D003035:Cobalt / Q000097:blood; D003430:Cross-Sectional Studies; D005260:Female; D006622:Hip Prosthesis; D006801:Humans; D007558:Italy; D008297:Male; D008670:Metals / Q000097:blood*; D008875:Middle Aged; D008982:Molybdenum / Q000097:blood; D011474:Prosthesis Design; D012189:Retrospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D012737:Sex Factors; D013997:Time Factors; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D008670:Metals; D002857:Chromium; D003035:Cobalt; D008982:Molybdenum