title: Two-year serum metal ion levels in minimally invasive total conservative hip resurfacing: preliminary results of a prospective study.
abstract: BACKGROUND
  Metal-on-metal (MoM) hip resurfacings have been associated with the potential development of metallic debris and its associated pathology. Serum cobalt and chromium levels are a reliable surrogate marker of wear rates in MoM bearings. The aim of the study was to examine the trend in serum metal ion levels in the initial 2-year post-operative period following implantation of the minimally invasive total conservative hip MoM hip resurfacing and to determine whether head size, acetabular component orientation, clinical outcome scores or post-operative range of movement would affect these levels.
  
  
  METHODS
  In this prospective cohort study, serum cobalt and chromium ion levels were measured pre- and post-operatively in 25 patients who underwent minimally invasive total conservative hip MoM hip resurfacing. The results were correlated with acetabular component orientation, head size, outcome scores and post-operative range of movement.
  
  
  RESULTS
  The mean serum cobalt and chromium levels at 2 years were 1.2 ppb (0.4-4.4 ppb) and 2.1 ppb (0.7-5.7 ppb). The mean cup inclination was 43° (30°-60°) and anteversion was 18° (1°-47°). There was no clear relationship between serum ions and acetabular component orientation, outcome scores or range of movement. Patients with a head size ≤52 mm had significantly higher metal ion levels (cobalt P = 0.02, chromium P = 0.045).
  
  
  CONCLUSIONS
  Our preliminary results show all patients had cobalt and chromium levels below those indicating a high-risk implant, suggesting successful early outcome from minimally invasive total conservative hip resurfacing surgery.
authors.affiliation: Mater Clinic, Specialist Orthopaedic Group, Sydney, New South Wales, Australia.
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Tai
authors.forename: Natascha
authors.initials: N
authors.lastname: Millard
authors.forename: Selin
authors.initials: S
authors.lastname: Munir
authors.forename: Amir R
authors.initials: AR
authors.lastname: Jenabzadeh
authors.forename: Leonard R
authors.initials: LR
authors.lastname: Walter
authors.forename: William L
authors.initials: WL
authors.lastname: Walter
mesh_terms: D000328:Adult; D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation* / Q000379:methods; D015415:Biomarkers / Q000097:blood; D002857:Chromium / Q000097:blood*; D003035:Cobalt / Q000097:blood*; D005500:Follow-Up Studies; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D061825:Metal-on-Metal Joint Prostheses; D008875:Middle Aged; D015207:Osteoarthritis, Hip / Q000601:surgery*; D011446:Prospective Studies; D011475:Prosthesis Failure; D016896:Treatment Outcome
chemical_list: D015415:Biomarkers; D002857:Chromium; D003035:Cobalt
keywords: chromium ion level; cobalt ion level; hip arthroplasty; metal-on-metal joint prosthesis