title: Cobalt serum levels differ in well functioning Birmingham resurfacing and Birmingham modular THA.
abstract: BACKGROUND
  Metal-on-metal (MoM) bearings are known to release metal ions secondary to wear and corrosion. This may cause local reactions (adverse soft tissue reactions and osteolysis) and systemic effects. Little is known about the exact pattern and the differences between large head MoM total hip replacements (THA) and resurfacings (HR).
  
  
  OBJECTIVE
  (1) Is there a difference in metal ion concentrations between HR and MoM-THR using the same bearing design (Birmingham Hip Resurfacing System, Smith & Nephew, Inc. Memphis, TN, USA)? (2) Are metal ion levels changing over time in MoM-THA or HR? (3) Do acetabular inclination angle and femoral component size influence cobalt and chromium levels? Is there a correlation between clinical outcome and metal ion levels?
  
  
  METHODS
  A retrospective analysis was conducted in 77 well functioning unilateral Birmingham HR and 42 well functioning unilateral modular Birmingham MoM-THA (Smith & Nephew, Inc. Memphis, TN, USA) operated on between 2007 and 2012. Blood samples were taken at a minimum of 13 months and subsequent during annual follow-ups.
  
  
  RESULTS
  (1) Cobalt levels were significantly higher in MoM-THA compared to HR (p < 0.001). There was no significant difference in chromium levels (p = 0.313). (2) Cobalt is increasing over time in MoM-THA (p = 0.030) whereas metal ions remain stable in HR. (3) Metal ion levels were not affected by acetabular inclination angle and femoral component size in MoM-THA. Chromium levels correlate with the femoral component size (r = -0.240; p = 0.037), the UCLA activity score (r = -0.344; p = 0.003) and the VAS (r = 0.263; p = 0.38) in HR.
  
  
  CONCLUSIONS
  Considering that HR and MoM-THA used the same MoM bearing design, increased cobalt levels may be related to trunnion wear or corrosion. Elevated cobalt levels should raise concern for corrosion related failure in MoM-THA.
authors.affiliation: Hospital for Special Surgery, 535 East 70th Street, New York, NY, 10021, USA.|Department of Orthopedic Surgery, Center for Musculoskeletal Surgery, Charite Universitaetsmedizin, Chariteplatz 1, 10117, Berlin, Germany.
authors.forename: Lisa
authors.initials: L
authors.lastname: Renner
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: Department of Orthopedic Surgery, University Hospital Muenster, Albert-Schweitzer-Campus 1, 48149, Münster, 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. boettnerf@hss.edu.
authors.forename: Friedrich
authors.initials: F
authors.lastname: Boettner
mesh_terms: D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000295:instrumentation*; D002857:Chromium / Q000097:blood; D003035:Cobalt / Q000097:blood*; D005260:Female; D006622:Hip Prosthesis / Q000009:adverse effects*; D006801:Humans; D007477:Ions / Q000097:blood; D008297:Male; D008875:Middle Aged; D011183:Postoperative Complications / Q000097:blood; D011474:Prosthesis Design; D012189:Retrospective Studies; D013997:Time Factors
chemical_list: D007477:Ions; D002857:Chromium; D003035:Cobalt
keywords: Cobalt; Metal ions; Metal-on-metal; Resurfacing; Total hip arthroplasty