Device Type, Blood Cobalt Levels Could Signal MoM Hip Failure

Elevated concentrations of cobalt in the blood and device type may predict early failure of metal-on-metal (MoM) hip replacements, according to British researchers.

“The results suggest that elevated blood metal ion concentrations are associated with early failure of [metal-on-metal] MoM devices secondary to adverse reactions to metal debris,” David J. Langton, M.R.C.S., and colleagues wrote in a recently published study.

Investigators performed a retrospective analysis of 299 resurfacings in 278 patients who underwent Articular Surface Replacement ([ASR] DePuy, Leeds, United Kingdom) and Birmingham Hip Resurfacing ([BHR] Smith & Nephew plc, Warwick, United Kingdom). The patients reported complications possibly related to metal wear debris and had “slight/occasional pain.” Harris Hip Scores were 95 or greater at the time of venesection. The researchers instituted a blood metal ion screening protocol, ultrasound scanning and joint aspiration to determine the blood cobalt concentration.

The patients followed up with their doctors on an annual basis unless their symptoms became to difficult to bear. Mean postoperative follow-up was 70 months and the mean follow-up post-venesection was 36 months.

Langton and colleagues found blood cobalt concentration and device to be significant risk factors for hip joint failure. They discovered females with high cobalt blood concentration and an ASR device had the highest failure risk while patients with the BHR device experienced an 89 percent reduced risk of revision.

“Cobalt concentrations greater than 20 μg/L are frequently associated with metal staining of tissues and the development of osteolysis,” the researchers wrote. “Development of soft tissue damage appears to be more complex with females and patients with ASR devices seemingly more at risk when exposed to equivalent doses of metal debris.”