26 July 2017
Metal-on metal (MoM) hip replacements
By Wendy Holden, Arthritis Action’s Medical Advisor
The Medicines and Healthcare products Regulatory Agency (MHRA) who licence all medicines and medical devices in the UK have in June 2017 published new guidelines for healthcare professionals caring for people who have had a commonly known as “metal-on metal” (MoM) hip replacement, where both the new hip socket and “ball” part of the hip joint are made of metal. This type of hip replacement was originally designed for younger people needing a hip replacement, for example sportsmen and women, as metal-on-metal hip replacements tend to last longer than the most common type of joint (made of metal on polyethylene), and therefore do not need replacing so often.
Most people who have MoM hip replacements have absolutely no problems with the new joint and are very happy with the results, but after MoM implants were introduced, especially one called the DePuy device in 2005, some patients started to feel more pain than is usual after a hip replacement. Gradually it was discovered that sometimes the tiny amounts of metal released during normal wear and tear of a MoM implant can trigger a reaction causing soft tissue or bone problems around the new joint. This can cause pain and swelling and sometimes means that the new joint has to be replaced. In 2010 the MHRA first issued an alert about MoM implants warning of possible complications, and suggested additional monitoring of patients having these new joints after surgery. These extra tests may include blood tests to check for levels of the two types of metal in the implant, nickel and chromium, and sometimes scans such as ultrasound or MRI.
Since 2010, the number of people in the UK having MoM implants has reduced significantly. In 2002 a National Joint registry of all patients having joint replacements in England, Wales, Northern Ireland and the Isle of Man was set up, and this looks at the types of surgery and monitors the outcomes. The latest joint registry report showed that in 2015, only 0.4% of people (4 in 1000) in the UK having the most common type of hip replacement had a MoM implant.
The 2017 MHRA guidelines which have updated existing guidelines suggests that people with MoM implants should have follow-up depending on the type of implant they have had (different manufacturers make different types of implant), and whether or not the hip is causing any problems. Some people need to be seen every year for blood test monitoring, and others can be reassured after a number of years if all is well and no further tests may be needed. Some patients may need further investigations, especially x-rays, ultrasound or MRI scans, especially if the new hip is painful, even if the levels of metals in the blood are normal.
If you have already had a MoM hip replacement, the team who performed the operation should be in contact with you and can give you more information. If you are not sure which type of hip replacement you have had, you can contact the hospital where the operation took place and they will be able to let you know.
If you are thinking of having a hip replacement operation and are worried, ask your surgeon for more information on the type of implant that he or she is planning to use and why. As MoM implants are now being used much less often, it is very unlikely that you will be offered this type of joint replacement, but don’t be afraid to ask for more information from your surgeon, especially about the number of similar procedures they perform every year and your surgeon’s own complication rate, as all surgeons should be happy to give you this information.