Hip replacement

Advice from the NHS on metal-on-metal hip implants, including what to do if you're concerned about your implant and warning signs to look out for.

Patients with a common type of metal hip implant should have regular health checks, according to the UK body for regulating medical devices.

Most people who have a metal-on-metal 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 a hip implant?

Metal-on-metal implants have only been used in a minority of all hip replacement surgeries, 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 signal a problem.

What are the warning signs?

You should contact your doctor if you have:

  • pain in the groin, hip or leg
  • swelling at or near the hip joint
  • a limp or problems walking
  • grinding or clunking from the joint

These symptoms don't necessarily mean your device is failing, but they do need investigating.

Any changes in general health should also be reported, including:

  • chest pain or shortness of breath
  • numbness or weakness
  • changes in vision or hearing
  • fatigue
  • feeling cold
  • weight gain

What are metal-on-metal implants?

As the name implies, metal-on-metal implants feature a joint made of two metal surfaces:

  • a metal "ball" that replaces the ball found at the top of the thigh bone (femur)
  • a metal "cup" that acts like the socket found 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 implants 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 exactly 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.

Data 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 MHRA guidance is designed to detect and treat any complications like this.

Metal ions in the bloodstream

Some news coverage has focused on the MHRA's recommendation to check for the presence of metal ions in the bloodstream.

Ions are electrically charged molecules. Levels of ions in the bloodstream, particularly of the 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 don't lead to sepsis, which is an entirely different type of illness. Talk of this in some of the 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 bloodstream 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 56,000 UK patients have a metal-on-metal hip device implanted.

The majority of these patients have well-functioning hips and a low risk of complications.

How are medical devices regulated?

In the UK, 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.

Further reading

British Orthopaedic Association: metal-on-metal hips

National Joint Registry: metal-on-metal hip implants

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