Patients with a common type of metal hip implant should have regular annual health checks.
Most people who have a metal-on-metal (MoM) implant have well-functioning hips and are thought to be at low risk of developing any serious problems.
But compared with other hip replacements, some metal-on-metal hip devices have been found to wear down more quickly in some patients.
This potentially causes damage and deterioration in the bone and tissue around the hip, which medical checks will monitor.
In 2017, the Medicines and Healthcare products Regulatory Agency (MHRA) published updated guidelines on monitoring patients with all types of metal-on-metal hip implants.
Check-ups are a precautionary measure to reduce the small risk of complications and monitor patients who have had the devices implanted for a long time.
What should I do if I have this type of hip implant?
Metal-on-metal (MoM) implants have only been used in a minority of all hip replacement surgeries. They are done on very few people now, so this may not affect you.
If you're not sure what type of implant you have or you have any concerns about your hip, you can consult your doctor for advice.
If you do have a metal-on-metal implant, make sure you attend any follow-up appointments you're invited to.
You should also be aware of the warning signs that could show there's a problem.
What are the warning signs?
You should contact your doctor if you have:
- pain in your groin, hip or leg
- swelling at or near your hip joint
- a limp or problems walking
- grinding or clunking from the joint
These symptoms do not necessarily mean your device is failing, but they do need to be investigated.
Any changes in your general health should also be reported, including:
- chest pain or shortness of breath
- numbness or weakness
- changes in vision or hearing
- feeling cold
- weight gain
What are metal-on-metal implants?
As the name implies, metal-on-metal implants are a joint made of two metal surfaces:
- a metal "ball" that replaces the ball at the top of the thigh bone (femur)
- a metal "cup" that acts like the socket in the pelvis
What does monitoring involve?
Patients who have metal-on-metal implants should be monitored regularly for the life of the implant and have tests to measure levels of metal particles (ions) in their blood.
Patients with these types of implant who have symptoms may be investigated with MRI or ultrasound scans, and patients without symptoms should have a scan if the level of metal ions in their blood is rising.
What is the problem with metal-on-metal implants?
Wear and tear
All hip implants wear down over time as the ball and cup slide against each other during movements, including walking and running.
Although many people live the rest of their lives without needing a replacement implant, some people may eventually need surgery to remove or replace its components.
Evidence suggests that certain types of metal-on-metal implant wear down at a faster rate than other types.
As friction acts upon their surfaces, it can cause tiny metal particles to break off and enter the space around the implant.
People are thought to react differently to the presence of these metal particles, but they can trigger inflammation and discomfort in the area around the implant in some people.
If not caught early, this can cause damage and deterioration in the bone and tissue surrounding the implant and joint over time. This in turn may cause the implant to become loose and cause painful symptoms, meaning further surgery is required.
The Medicines and Healthcare products Regulatory Agency (MHRA) guidance is designed to detect and treat any complications like this.
Metal ions in the blood
Some news coverage has focused on the MHRA's recommendation to check for the presence of metal ions in the blood.
Ions are electrically charged molecules. Levels of ions in the blood, particularly of cobalt and chromium used in the surface of the implants, may therefore indicate how much wear there is to the artificial hip.
These ions in the blood are not blood poisoning and do not lead to sepsis, which is an entirely different type of illness. Talk of this in some news reports is very misleading and completely wrong.
There has been no definitive link between ions from metal-on-metal implants and illness, although there has been a small number of cases in which high levels of metal ions in the blood have been associated with symptoms or illnesses elsewhere in the body, including effects on the heart, nervous system and thyroid gland.
How many people are affected?
Approximately 71,000 UK patients have had a metal-on-metal hip device implanted or had metal-on-metal resurfacing.
The majority of these patients have well-functioning hips and a low risk of complications.
Because of the problems with this type of implant, they are rarely used now.
How are medical devices regulated?
In the UK, the MHRA is the government agency responsible for ensuring medical devices work and are safe. MHRA audits the performance of private sector organisations that assess and approve medical devices.
Once a product is on the market and in use, MHRA has a system for receiving reports of problems with these products and will issue warnings if these problems are confirmed through its investigations.
It also inspects companies that manufacture products to ensure they comply with regulations.
National Joint Registry: metal-on-metal hip implants
Page last reviewed: 23 December 2019
Next review due: 23 December 2022