title: Do cobalt and chromium levels predict osteolysis in metal-on-metal total hip arthroplasty?
abstract: BACKGROUND
  Serum metal ions are part of the regular follow-up routine of patients with metal-on-metal total hip arthroplasties (MoM-THA). Increased cobalt levels have been suggested to indicate implant failure and corrosion.
  
  
  OBJECTIVE
  (1) Is there a correlation between the size of the osteolysis measured on a CT scan and metal ion levels? (2) Can metal ion levels predict the presence of osteolysis in MoM-THA? (3) Are cobalt and chromium serum levels or the cobalt-chromium-ratio diagnostic for osteolysis?
  
  
  METHODS
  CT scans of patients (n = 75) with a unilateral MoM-THA (Birmingham Hip System, Smith & Nephew, TN, USA) implanted by a single surgeon were reviewed to determine the presence of osteolysis. Statistical analysis was performed to detect its association with metal ion levels at the time of the imaging exam.
  
  
  RESULTS
  The incidence of osteolysis was the same in men and women (35.6 vs 35.7 %). The cobalt-chromium-ratio correlates with the size of the osteolysis on the CT scan and the femoral component size in the overall study population (p = 0.050, p = 0.001) and in men (p = 0.002, p = 0.001) but not in women (p = 0.312, p = 0.344). The AUC for the cobalt-chromium-ratio to detect osteolysis was 0.613 (p = 0.112) for the overall population, 0.710 for men (p = 0.021) and 0.453 (p = 0.684) for women. The data suggest that a cut off level of 1.71 for the cobalt-chromium-ratio has a sensitivity of 62.5 % and specificity of 72.4 % to identify male patients with osteolysis.
  
  
  CONCLUSIONS
  The disproportional increase of cobalt over chromium, especially in male patients with large component sizes can not be explained by wear alone and suggests that other processes (corrosion) might contribute to metal ion levels and might be more pronounced in patients with larger component sizes.
authors.affiliation: Hospital for Special Surgery, 535 East 70th Street, New York, NY, 10021, USA.|Department of Orthopedic Surgery, Center for Musculosceletal Surgery, Charite Universitaetsmedizin, Chariteplatz 1, 10117, Berlin, Germany.
authors.forename: Lisa
authors.initials: L
authors.lastname: Renner
authors.affiliation: Department of Orthopedics, University of Muenster, Albert Schweitzer-Campus 1, 48149, Muenster, Germany.
authors.forename: Tom
authors.initials: T
authors.lastname: Schmidt-Braekling
authors.affiliation: Hospital for Special Surgery, 535 East 70th Street, New York, NY, 10021, USA.|Department of Orthopedics and Orthopedic Surgery, University of Ulm, Oberer Eselsberg 45, 89081, Ulm, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Faschingbauer
authors.affiliation: Hospital for Special Surgery, 535 East 70th Street, New York, NY, 10021, USA. boettnerf@hss.edu.
authors.forename: Friedrich
authors.initials: F
authors.lastname: Boettner
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D015415:Biomarkers / Q000097:blood; D002857:Chromium / Q000097:blood*; D003035:Cobalt / Q000097:blood*; D005260:Female; D005858:Germany / Q000453:epidemiology; D006622:Hip Prosthesis; D006801:Humans; D015994:Incidence; D008297:Male; D061825:Metal-on-Metal Joint Prostheses; D008875:Middle Aged; D010014:Osteolysis / Q000097:blood* / Q000175:diagnosis / Q000453:epidemiology; D011183:Postoperative Complications; D014057:Tomography, X-Ray Computed
chemical_list: D015415:Biomarkers; D002857:Chromium; D003035:Cobalt
keywords: CT scan; Metal ions; Metal-on-metal; Osteolysis; Total hip arthroplasty