title: Relationship of plasma metal ions and clinical and imaging findings in patients with ASR XL metal-on-metal total hip replacements.
abstract: BACKGROUND
  Plasma metal ion levels are commonly used in the postoperative follow-up evaluation of patients who have had a metal-on-metal hip arthroplasty. However, the relationship between these levels and clinical and imaging findings is not well known.
  
  
  METHODS
  We evaluated 156 consecutive patients who received a unilateral ASR XL total hip replacement. Patients presented, regardless of symptoms, in response to a voluntary recall of the hip replacement by the manufacturer and were assessed with regard to the presence and type of symptoms and plasma cobalt-chromium levels. In addition, radiographic and magnetic resonance imaging studies were performed and analyzed.
  
  
  RESULTS
  Eighty patients were asymptomatic, and seventy-six patients were symptomatic. The median cobalt level was 1.8 ppb, and the median chromium level was 1.0 ppb (at or below measurement threshold). Pseudotumors that could be detected on magnetic resonance imaging were seen in 69% (107) of 156 patients, and radiographic osteolysis was evident in 7% (eleven patients). At a threshold of 5 ppb, no association was detected between abnormal metal ion levels and patient symptoms, prosthetic femoral head size, or acetabular cup inclination. An abnormal cobalt level was significantly associated with the presence of periprosthetic lucency on radiographs and pseudotumor on magnetic resonance imaging (p < 0.05). An abnormal chromium level showed a similar pattern, but the relationships did not reach significance. Both abnormal plasma cobalt and chromium levels were associated with larger sizes of pseudotumor when present (p < 0.05).
  
  
  CONCLUSIONS
  In our sample, with a threshold of 5 ppb, abnormal plasma metal ions were associated with larger sizes of pseudotumors when present, but were not predictive of patient symptoms. Abnormal plasma cobalt levels have a significant association with periprosthetic lucency and presence of pseudotumor. Plasma chromium shows a similar pattern of association with lucency and presence of pseudotumor, although the relationships were not significant. Metal ion analysis should be used in conjunction with clinical and imaging evaluation and not as a sole indirect screening test when evaluating patients following metal-on-metal hip arthroplasty.
authors.affiliation: VA San Diego Healthcare System, 3350 La Jolla Village Drive, San Diego, CA 92161.
authors.forename: Eric Y
authors.initials: EY
authors.lastname: Chang
authors.forename: James L
authors.initials: JL
authors.lastname: McAnally
authors.forename: James R
authors.initials: JR
authors.lastname: Van Horne
authors.forename: James G
authors.initials: JG
authors.lastname: Van Horne
authors.forename: Tanya
authors.initials: T
authors.lastname: Wolfson
authors.forename: Anthony
authors.initials: A
authors.lastname: Gamst
authors.forename: Christine B
authors.initials: CB
authors.lastname: Chung
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip; D001672:Biocompatible Materials; D002857:Chromium / Q000097:blood*; D003035:Cobalt / Q000097:blood*; D005260:Female; D006104:Granuloma, Plasma Cell / Q000175:diagnosis*; D006615:Hip / Q000000981:diagnostic imaging*; D006622:Hip Prosthesis; D006801:Humans; D007477:Ions / Q000097:blood; D008279:Magnetic Resonance Imaging; D008297:Male; D008670:Metals; D008875:Middle Aged; D011474:Prosthesis Design; D011475:Prosthesis Failure; D011859:Radiography
chemical_list: D001672:Biocompatible Materials; D007477:Ions; D008670:Metals; D002857:Chromium; D003035:Cobalt