Triad in neuropathy from metal on metal hips

The review of the controversy surrounding the articular surface replacement hip prosthesis is timely.1 Such metal on metal prostheses have become popular over the past decade and are now present in many patients who visit their GP for other reasons. At our specialist hospital we have seen many patients with unexpected complications from such prostheses.

It became apparent that many patients came to us by a very convoluted route. Many patients had no pain around their hip but had both central and peripheral neuropathies. The mechanism behind neuropathy is poorly understood but may involve direct neurotoxicity, pressure effects of wear debris, or hypersensitivity reactions.2 3 4 Patients were often referred to us by local neurologists after extensive investigations that took weeks or months.

Delays in presentation undoubtedly lead to a poorer outcome. We have therefore developed a simple diagnostic triad to help recognise the metal on metal bearing as a possible cause of unexplained neurological pathology. This triad consists of:

• Unexplained neurology

• Raised serum cobalt or chromium ion concentrations (or both)

• The presence of a metal bearing hip prosthesis.

If all three factors are present, urgently refer the patient to a specialist orthopaedic surgeon for further investigation and consideration of exchange arthroplasty.