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Blood Metal Ion Levels as Predictors of Hip Implant Failure

Jul 15, 2014

A Finnish research team carried out a study to assess whether blood metal ion levels could predict hip implant failure in patients who received metal-on-metal hip implants.

Five hundred and ninety-seven patients who had received unilateral Articular Surface Replacement devices at least twelve months earlier were recruited for the study, according to The Journal of Bone & Joint Surgery. Blood metal ion levels were compared between the group of patients with failed implants and the group whose implants did not fail. Implant failure was defined as prostheses associated with revision surgery, intention to revise, or poor patient-reported hip function (Oxford Hip Score, <31 of 48).

Patients with failed implants had significantly higher blood cobalt and chromium ion levels than did patients with non-failed implants (p < 0.01), according to the journal. Blood cobalt ion levels were disproportionately raised in patients with failed total hip arthroplasty (8.2 μg/L) compared with patients with failed hip resurfacing (2.5 μg/L) (p = 0.018). The maximum value of either metal ion had good discriminant ability to predict implant failure (area under the curve, 0.76). A 7-μg/L cutoff had a positive predictive value of 0.75 (95% confidence interval, 0.66 to 0.82) and a negative predictive value of 0.82 (95% confidence interval, 0.78 to 0.86). In patients with total hip arthroplasty, for each increase of 1 μg/L there was a 23% (p < 0.001) increase in the odds of them being in the failed group. For patients managed with hip resurfacing, the increase in odds was 5% (p < 0.001).

Metal-on-metal hips have been shown to be prone to early failure, with recipients suffering pain, difficulty walking, soft tissue damage and death, bone loss, and cysts around the joint, as well as elevated metal ion levels. Many of these hip implants have been withdrawn from the market and thousands of lawsuits have been filed against the manufacturers.

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