Monitoring metal hip replacements

PATIENTS with metal-on-metal (MoM) hip implants should receive regular physical examinations, x-rays and soft tissue imaging. Perform chromium and cobalt blood levels at least once a year and if rising, increase screening frequency to three monthly.1

Refer people who show increasing serum levels of chromium and/or cobalt on serial review to the treating surgeon for further investigation.2 Consistently rising blood levels of chromium or cobalt ions (after the first 18 months, known as the ‘run-in period’) can reflect accelerated wear, and may indicate that the implant is starting to fail.1,2 

There are also concerns that increasing levels of chromium and cobalt ions may cause systemic toxicity. Normal serum levels of cobalt and chromium are 0–20nmol/L and 0–100nmol/L respectively.3 There is no consensus on threshold levels of cobalt and chromium above which systemic toxicity may occur.1

The link between elevated levels of chromium and