Topic Reliability

Executive Summary

Systemic cobalt toxicity from total hip arthroplasty. Review of a rare condition part 2: Measurement, risk factors, and step-wise approach to treatment.

Authors
M.G. Zywiel, J.J. Cherian, S. Banerjee, A.C. Cheung, F. Wong, J. Butany, C. Gilbert, C. Overgaard, K. Syed, J.
J. Jacobs, M. A. Mont – Rubin Institute for Advanced Orthopedics, Baltimore, USA
Journal
Bone & Joint Journal 2016; 98-B(1): 14-20
Level of Evidence
Level IV: unsystematic review of case series.

Summary

Zywiel et al reviewed the literature to examine the use of Co-alloys in THA and methods of measuring circulating cobalt levels to define a level, which is considered pathological, as well as review the pathophysiology, risk factors and treatment of cobalt toxicity. They identified 18 published cases in THA. Most of these cases reported systemic toxic reactions at cobalt levels greater than 100μg/L.

Cobalt ion levels can be measured from whole blood, serum or erythrocytes. However, the values cannot be used interchangeably. Different units are used for cobalt levels, which are easily convertible: 1ppb = 1μg/L = 1ng/ml; which is approx. 16.97nmol/L. The natural level of Co in serum is believed to be about 0.1 ppb. The authors were not able to define a pathological Co ion level since it is highly likely that the systemic risks from
Co ion release is complicated by patient-specific factors that increase or decrease susceptibility.

From the eighteen cases of systemic Co toxicity described with elevated Co levels and multisystem effects, eight were related to the use of metal-on-polyethylene (MoP) bearings in revision THA for ceramic fracture, one even fatal. The other ten cases were judged to be potentially malfunctioning MoM bearings. In all cases serum Co levels decreased after revision. Based on their review the authors state that drawing conclusions about the relationship between elevated Co levels and systemic symptoms is limited.

Study Limitations

Key Messages

Commentary

The case reports extracted from the literature were insufficient to determine a cause and effect between Co levels and the patient’s reported symptoms. Although the paper is only a summary of case reports, it shows the risk of using CoCr femoral heads in revisions for ceramic fracture.

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