Metal On Metal Total Hip Replacements Unsafe?

A BBC Newsnight and British Medical Journal investigation has prompted a lot of discussion regarding metal on metal total hip replacements. Lately, a study has found that the metal components rub against each other causing small particles to break away into surrounding tissues. This leads to elevated blood levels of metal ions such as cobalt and chromium. The clinical significance of this is still unknown. The Medicines and Healthcare products Regulatory Agency (MHRA) have stated that annual blood tests should be conducted to check levels of cobalt and chromium. If levels are high, an MRI scan should be carried out to see if the prosthesis requires revision.

A recent technology overview conducted by the American Academy of Orthopaedic Surgeons (AAOS) has concluded that metal on metal implants are at greater risk of revision than replacements with different bearing surface combinations. This has come as a bit of a surprise as it was hoped that sturdy metal on metal implants would outlast metal on plastic implants. It was also noted that larger femoral head components are at higher risk than smaller ones and older patients also incur a greater likelihood of requiring another operation.

A previous technology review had found that hip resurfacing is more likely to need revising than total hip arthroplasties (THA). The size of the head is inversely related to the risk of revision. However, the Australian registry has suggested that younger men have less risk of revision with resurfacing than they do with THAs. This is interesting because research published in this month’s The Journal of Bone & Joint Surgery (British Volume) shows that the 10 year survival rate for a Birmingham hip resurfacing (BHR) is 89.1% for women and 97.5% for men. Mr AJ Shimmin et al. conclude that “BHR provides good functional outcome and durability for men, at a mean follow-up of ten years. We are now reluctant to undertake hip resurfacing in women with this implant”.

All this definitely provides food for thought and it’s well worth doing some research and having a long chat with your surgeon before deciding what sort of hip prosthesis to have.