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.

Should You Run After A Hip Resurfacing?

Osteoarthritis is the gradual degradation of a joint. It can lead to pain, stiffness and swelling. One of the most common joints to be affected is the hip. In 1940 Dr Austin Moore performed the first total hip replacement (THR) and the technique was later refined by Dr John Charnley. Modern replacements consist of a metal stem and head that is inserted into the top of the femur. It fits into a plastic cup which is cemented into the pelvis. Post surgery, patients usually experience less pain and enjoy greater range of motion. However, several studies have shown that the prosthesis wears and loosens prematurely if excessive running and impact activities are undertaken. This can lead to another operation to revise the THR with the associated risk of complications.

More recently, hip resurfacing was developed by Dr Derek McMinn as an alternative to THRs. It requires less of the femur to be removed. A metal cap is placed over the head of the femur and a metal cup is placed in the socket. The advantages of a hip resurfacing compared to a THR are numerous: bone preservation, less chance of dislocation, less leg length inequality, better lower limb alignment and easier revision to a THR if necessary.

A recent article in Reuters has quoted work done by Dr Julien Girard in France. Hip resurfacings were performed on 40 physically active patients. Their average age was 51 years. After surgery, 90% of the patients returned to running. Three years later 33 out of 40 were still running albeit they had decreased their mileage from 24 miles per week to 16 miles per week. The study didn’t look at the long-term effects of running on the implant.

An article in today’s Medical News Today summarises research presented at the 2012 Annual Meeting of the Academy of Orthopaedic Surgeons.  Over 10 years, 445 patients (average age of 49 years) who had undergone a hip resurfacing were monitored. A correlation between higher activity scores and revision of surgery was found and it was concluded that impact activities such as running and tennis were harmful to long-term success.

In conclusion, although a return to running and impact sports is possible after a hip resurfacing…even to high level competitive sport…it does bear risks…such as the untimely wear and deterioration of the prosthesis. This would require further surgery…and possibly a total hip replacement. With that in mind, my advice for anyone with a hip resurfacing, wondering how much they can or can’t do…would be to stick to non-impact exercise such as cycling, rowing, cross-training, etc. That doesn’t mean that you shouldn’t run at all…I wouldn’t want you to miss that train…but it should remain occasional.