title: Sensitivity and specificity of blood cobalt and chromium metal ions for predicting failure of metal-on-metal hip replacement.
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.
authors.affiliation: Imperial College London, Department of Musculoskeletal Surgery, Charing Cross Hospital Campus, Fulham Palace Road, London W6 8RF, UK. a.hart@imperial.ac.uk
authors.forename: A J
authors.initials: AJ
authors.lastname: Hart
authors.forename: S A
authors.initials: SA
authors.lastname: Sabah
authors.forename: A S
authors.initials: AS
authors.lastname: Bandi
authors.forename: P
authors.initials: P
authors.lastname: Maggiore
authors.forename: P
authors.initials: P
authors.lastname: Tarassoli
authors.forename: B
authors.initials: B
authors.lastname: Sampson
authors.forename: J
authors.initials: J
authors.lastname: A Skinner
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation; D015415:Biomarkers / Q000097:blood; D016022:Case-Control Studies; D002857:Chromium / Q000097:blood*; D003035:Cobalt / Q000097:blood*; D005260:Female; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D011474:Prosthesis Design; D011475:Prosthesis Failure / Q000209:etiology*; D012086:Reoperation; D012680:Sensitivity and Specificity; D055815:Young Adult
chemical_list: D015415:Biomarkers; D002857:Chromium; D003035:Cobalt