TP6.1 Outcome-Validated Cobalt Surveillance Thresholds for Metal-on-Metal Hip Resurfacing: Defining Normal Bearing Function

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ID: 331044
2026
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Abstract
Abstract Introduction Whole blood cobalt testing is central to the surveillance of metal-on-metal (MoM) hip resurfacing arthroplasty (HRA). However, no validated cobalt reference ranges exist for well-functioning MoM implants; standard laboratory normals apply to implant-free individuals and systematically misclassify modest elevations as abnormal, leading to unnecessary patient anxiety and premature revision in otherwise well-functioning patients. Adverse wear-related failure (AWRF) and trunnion corrosion failure (TCF) have distinct ion profiles, yet no large outcome-correlated dataset has defined diagnostic thresholds. This study provides an evidence base for cobalt surveillance in the post-resurfacing patient. Methods Whole blood cobalt levels obtained 1–5 years postoperatively were retrospectively analysed from a prospectively maintained single-surgeon database of MoM hip arthroplasties. Cohorts of HRA and total hip arthroplasty (THA) patients with confirmed implant survivorship at 10 and 15 years provided outcome-correlated reference values. These were compared against patients who experienced AWRF, TCF, or other failure modes. Activity-stratified analyses evaluated whether physical activity level influenced early cobalt levels. Results In over 1000 well-functioning HRAs at 10–15 years, mean early cobalt was 1.2 ± 1.2 μg/L (unilateral); all remained below 14 μg/L. THA cohorts had comparable levels, all below 14 μg/L. TCF cases showed intermediate cobalt (mean 5.3 ± 2.0 μg/L) overlapping with the successful range. All AWRF cases had cobalt ≥15 μg/L (mean 71.7 ± 47.9 μg/L; range 15.0–152.6 μg/L), with no overlap with successful implants. High- and low-activity patients showed no significant difference in early cobalt levels. Conclusion Cobalt below 14 μg/L confirms normal MoM HRA bearing function; cobalt ≥15 μg/L reliably identifies AWRF with no false negatives in this series. TCF cannot be diagnosed by cobalt alone and requires clinical and imaging correlation. For preservation surgeons managing the post-resurfacing patient (who are often young and active), these outcome-validated thresholds provide more applicable metal ion ranges for surveillance. Routine cobalt testing around two years postoperative may serve as a useful screening tool to confirm appropriate bearing function and improve diagnosis of abnormal wear failure.
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Authors Dani Gaillard-campbell, Thomas Gross
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Journal Journal of hip preservation surgery
Year 2026
DOI
10.1093/jhps/hnag043.164
URL
https://doi.org/10.1093/jhps/hnag043.164
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