The latest developments in Metal-on-Metal Hip Replacements
Despite the fact that there was no evidence of metallic debris in the body, a small number of hip replacement patients reported problems such as dislocation, fractures and infection. Smith & Nephew’s chief medical officer is reported as saying that the decision had been taken following clinical studies which revealed that 1.6% of patients with the optional metal liner, or cup, component of its R3 Acetabular System needed revision surgery each year. This figure is above the 1% guideline set by the National Institute for Health and Clinical Excellence (NICE) and was therefore deemed unsatisfactory.
According to figures released by the MHRA, post-market surveillance data has identified a revision rate of 6.3% at four years for patients implanted with the R3 metal liner. The guidance figure set by NICE is 4% at four years. The MHRA has therefore told surgeons to stop using the metal cup liner and to monitor the 281 patients who have been fitted with these cup liners annually so that any complications can be dealt with at the earliest opportunity.
The MHRA’s Clinical Director of Medical Devices, Dr Susanne Ludgate, released the following statement:
“In the UK, 281 patients have been fitted with this specific R3 metal cup liner. Evidence from post market surveillance data has shown that the revision rate for this implant is high and that is why we have taken action to advise surgeons to stop using this device and to monitor the patients implanted with this cup liner on an annual basis.
“Clinical evidence shows that patients have a small risk of suffering complications from having metal-on-metal hip implants but we believe, after advice from our expert advisory group, that it makes sense for surgeons to annually monitor any patients who are showing any symptoms such as pain or swelling if they have metal-on-metal hip implants. By monitoring patients with symptoms every year, any complications will get picked up and they can be treated earlier.”
Although there is a specific issue with the R3 metal cup liner, news of this recall will fan the flames of the increasing controversy surrounding MoM hip implants. It is recognised that some MoM patients do suffer from problems as a result of the build-up of metallic debris caused by the wearing of the device. This debris can cause inflammation and discomfort in the surrounding area, and over time, cause damage to the bone and muscle. This can lead to the implant becoming loose and causing pain, dislocation or fracture, which will require revision surgery.
There is also concern about the levels of cobalt and chromium ions in the bodies of those with MoM hips, especially where the implants have been worn away. Side effects of cobalt toxicity include nerve damage, nausea, vomiting, thyroid disorders and cardiovascular damage. Chromium can cause problems with the lungs and reproductive system. The US Food and Drug Administration (FDA) recommends that MoM hips should not be fitted into women of child-bearing age.
Regardless of the type of MoM prosthesis, the MHRA’s current advice for patients with symptoms is that they:-
- are checked annually for the life of the implant
- have an ultrasound, MRI or MARS scan
- have a blood test to measure the levels of metal ions present
- have a second blood test three months later if the level was 7ppb or more
- consider revision surgery if the scans or blood tests indicate abnormalities
The same advice applies to those asymptomatic patients who have been fitted with all types of DePuy ASR hip replacements.
For asymptomatic patients with Stemmed MoM total hip replacements with a femoral head diameter of 36mm or greater, the same advice applies except that scans are recommended only if blood metal ion levels are shown to be rising.
For asymptomatic patients with no-stem MoM hip resurfacing, or Stemmed MoM total hip replacements with a femoral head less than 36mm in diameter, imaging and blood tests are not recommended unless there are other health-concerns or the patient develops symptoms. Patient follow-ups will be subject to local regulations.
