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.

MRI Predicts ALVAL and Tissue Damage in Metal-on-Metal Hip Arthroplasty

“…We found sensitivity and specificity of 94% and 87%, respectively, for detecting ALVAL and 90% and 86%, respectively, for quantifying tissue damage. These values are a major improvement on the predictive ability of blood cobalt and chromium ion levels for identifying a failing hip implant, which have sensitivity and specificity of 63% and 86%, respectively [9]. Other groups have used MRI to study soft tissue lesions around MOM hip implants, but none has used quantitative, reproducible MRI features and none has compared findings between groups formed on a histologic diagnosis [5,8,11,27,30,35].…”

The Surgical Options and Clinical Evidence for Treatment of Wear or Corrosion Occurring With THA or TKA

“…Many of the studies we identified also mentioned the use of metal level testing. Currently, there are efforts focusing on management of patients with MoM implants that include guidelines for the use and importance of metal levels that will help surgeons counsel patients and use the levels as one of many tools to help determine when to intervene [22,26]. Lastly, the one case series on corrosion is interesting because it highlights the relative increase in cobalt levels compared to chromium levels in situations where corrosion is the process driving particle generation and failure [10].…”

Diagnosis of adverse local tissue reactions following metal-on-metal hip arthroplasty

“…While there are no studies directly defining the exact correlation of elevated metal ion levels and increased risk ALTR, several reports have shown that elevated metal ion levels are associated with increased wear rates and failed MOM prostheses [20, 16•, 11, 19]. Several studies have shown that cobalt levels above 7 parts-per-billion (ppb) [16•, 20, 11] are a reasonable threshold for increased concern and closer clinical follow-up, while other studies suggest cobalt levels of 4.5 ppb [18,19]. Therefore, the results of metal ion levels are best used as another data point in the context of a risk stratification model, rather than absolute numbers [11•, 16•, 18].…”