Arthroprosthetic cobaltism associated with metal on metal hip implants

Our initial experience with metal on metal hip implants1 was favourable. But several years later an uncharacteristically high proportion of patients developed progressive, unresolved, or new hip pain, some showing metal debris around the hip with tissue damage. Two patients had remarkably high cobalt concentrations, cognitive decline, cranial neuropathy, and early cardiomyopathy.2

We have just identified a fifth case of probable arthroprosthetic cobaltism in a patient awaiting revision of a Birmingham hip resurfacing arthroplasty. The device functioned well for 15 months, and he remained well. Over the next 23 months he developed pain and noise at the hip, new onset of anxiety and major depression, tinnitus, high frequency hearing loss (audiographically confirmed), peripheral neuropathy, and cognitive decline. Serum cobalt concentrations ranged between 64 and 74 µg/L three years after implantation (normal values <1 µg/L).

Two of our five patients received articular surface replacement and three a Birmingham metal-metal hip. All had a prodrome of depression and anxiety. Four later developed tinnitus, and one had new onset vertigo. Four had notable high frequency hearing loss on audiography. Three had early cardiomyopathy. Two required increased drug treatment for hypertension. Two developed hypothyroidism and one hyperparathyroidism. Four patients had hip noise or pain before new neurological, cardiovascular, or endocrine problems were noted. The other had no hip symptoms but had notable periprosthetic tissue damage at revision surgery.

Four patients received ceramic-plastic hip revision. Histopathology showed metallosis, necrosis, and chronic inflammation. Serum cobalt concentrations fell rapidly in all of them, although values were still toxic (>5 µg/L) in one patient a year later. In the two previously reported cases, neurological and cardiovascular function had improved significantly two years after revision.

Patients with arthroprosthetic cobaltism may present with new neurologic, cardiovascular, or endocrine problems with or without symptoms attributable to their prosthetic hip. Blood cobalt concentrations greater than 10 µg/L would support this suspicion.