Sensitivity and specificity of blood cobalt and chromium metal ions for predicting failure of metal-on-metal hip replacement

J Bone Joint Surg Br. 2011 Oct;93(10):1308-13. doi: 10.1302/0301-620X.93B10.26249.

Abstract

Blood metal ions have been widely used to investigate metal-on-metal hip replacements, but their ability to discriminate between well-functioning and failed hips is not known. The Medicines and Healthcare products Regulatory Agency (MHRA) has suggested a cut-off level of 7 parts per billion (ppb). We performed a pair-matched, case-control study to investigate the sensitivity and specificity of blood metal ion levels for diagnosing failure in 176 patients with a unilateral metal-on-metal hip replacement. We recruited 88 cases with a pre-revision, unexplained failed hip and an equal number of matching controls with a well-functioning hip. We investigated the 7 ppb cut-off level for the maximum of cobalt or chromium and determined optimal mathematical cut-off levels from receiver-operating characteristic curves. The 7 ppb cut-off level for the maximum of cobalt or chromium had a specificity of 89% and sensitivity 52% for detecting a pre-operative unexplained failed metal on metal hip replacement. The optimal cut-off level for the maximum of cobalt or chromium was 4.97 ppb and had sensitivity 63% and specificity 86%. Blood metal ions had good discriminant ability to separate failed from well-functioning hip replacements. The MHRA cut-off level of 7 ppb provides a specific test but has poor sensitivity.

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Arthroplasty, Replacement, Hip / instrumentation
  • Biomarkers / blood
  • Case-Control Studies
  • Chromium / blood*
  • Cobalt / blood*
  • Female
  • Hip Prosthesis*
  • Humans
  • Male
  • Middle Aged
  • Prognosis
  • Prosthesis Design
  • Prosthesis Failure / etiology*
  • Reoperation
  • Sensitivity and Specificity
  • Young Adult

Substances

  • Biomarkers
  • Chromium
  • Cobalt