title: Mid-term changes in blood metal ion levels after Articular Surface Replacement arthroplasty of the hip.
abstract: OBJECTIVE
  Our first aim was to determine whether there are significant changes in the level of metal ions in the blood at mid-term follow-up, in patients with an Articular Surface Replacement (ASR) arthroplasty. Secondly, we sought to identify risk factors for any increases.
  
  
  METHODS
  The study involved 435 patients who underwent unilateral, metal-on-metal (MoM) hip resurfacing (HRA) or total hip arthroplasty (THA). These patients all had one measurement of the level of metal ions in the blood before seven years had passed post-operatively (early evaluation) and one after seven years had passed post-operatively (mid-term evaluation). Changes in ion levels were tested using a Wilcoxon signed-rank test. We identified subgroups at the highest risk of increase using a multivariable linear logistic regression model.
  
  
  RESULTS
  There were significant increases in the levels of metal ions for patients who underwent both MoM HRA (Chromium (Cr): 0.5 parts per billion (ppb); Cobalt (Co): 1.1 ppb) and MoM THA (Cr: 0.5 ppb; Co: 0.7 ppb). In a multivariable model considering MoM HRAs, the change in the levels of metal ions was influenced by female gender (Co: Odds Ratio (OR) 1.42; p = 0.002 and Cr: OR 1.08; p = 0.006). The change was found to be irrespective of the initial level for the MoM HRAs, whereas there was a negative relationship between the initial level and the change in the level for those with a MoM THA (Co: OR -0.43; p < 0.001 and Cr: OR -0.14; p = 0.033).
  
  
  CONCLUSIONS
  The levels of metal ions in the blood increase significantly over the period until mid-term follow-up in patients with both a MoM HRA and those with a MoM THA. We recommend that the levels of metal ions be measured most frequently for women with a MoM HRA. While those with a MoM THA appear to stabilise at a certain level, the accuracy of this trend is not yet clear. Vigilant follow-up is still recommended. Cite this article:Bone Joint J2017;99-B(4 Supple B):33-40.
authors.affiliation: Massachusetts General Hospital, Harris Orthopaedic Laboratory, 55 Fruit St. GRJ 1231, Boston, MA 02114, USA.
authors.forename: V P
authors.initials: VP
authors.lastname: Galea
authors.affiliation: Harvard Medical School, 25 Shattuck St, Boston, MA 02115, USA.
authors.forename: I
authors.initials: I
authors.lastname: Laaksonen
authors.affiliation: Massachusetts General Hospital, Harris Orthopaedic Laboratory, 55 Fruit St. GRJ 1231, Boston, MA 02114, USA.
authors.forename: S J
authors.initials: SJ
authors.lastname: Matuszak
authors.affiliation: Massachusetts General Hospital, Harris Orthopaedic Laboratory, 55 Fruit St. GRJ 1231, Boston, MA 02114, USA.
authors.forename: J W
authors.initials: JW
authors.lastname: Connelly
authors.affiliation: Harvard Medical School, 25 Shattuck St, Boston, MA 02115, USA.
authors.forename: O
authors.initials: O
authors.lastname: Muratoglu
authors.affiliation: Harvard Medical School, 25 Shattuck St, Boston, MA 02115, USA.
authors.forename: H
authors.initials: H
authors.lastname: Malchau
mesh_terms: D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects* / Q000295:instrumentation / Q000379:methods; D002857:Chromium / Q000097:blood*; D003035:Cobalt / Q000097:blood*; D005260:Female; D005500:Follow-Up Studies; D006622:Hip Prosthesis / Q000009:adverse effects*; D006801:Humans; D008297:Male; D061825:Metal-on-Metal Joint Prostheses / Q000009:adverse effects; D008875:Middle Aged; D011446:Prospective Studies; D011474:Prosthesis Design; D012307:Risk Factors; D012737:Sex Factors
chemical_list: D002857:Chromium; D003035:Cobalt
keywords: Hip resurfacing arthroplasty; Metal ion levels; Metal-on-metal; Total hip arthroplasty