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Metal-on-metal hip replacement Q & A

Answers provided by John Skinner, consultant orthopaedic surgeon at Royal National Orthopaedic Hospital, Stanmore, UK, and Alister Hart, professor of orthopaedic surgery at UCL and Royal National Orthopaedic Hospital, London, UK.

What are the concerns about metal-on-metal hips?

When they work well, metal-on-metal (MoM) hip resurfacing and total hip replacements give years of trouble-free use with very low levels of wear. However, some MoM implants can fail, increasing the amount of wear and producing small amounts of debris. This debris is particles (ions) of cobalt and chromium that make up the implant. This debris can trigger a response in your body, which can cause erosion of bone, damage to muscle and loosening of the implants.

The National Joint Registry 13th annual report, published in 2016, states that 17.65% of MoM hip implants fail after 10 years – this is approximately three times greater than for other hip types. However, there is considerable variation in the failure rate of MoM hips with poorer results in the ASR hip, particularly with smaller sizes and in women.

In most people the metal ions are absorbed into the bloodstream, then filtered by the kidneys and passed out in the urine. By measuring the concentration of these ions in the blood we can discover how the hip is wearing. These levels are very low and are measured in parts per billion (ppb) or nmol/L, and are typically 2 ppb or approximately 30 nmol/L in a well functioning hip. However, the concentration of metal ions in the fluid around the hip joint can be much higher. It's thought that these higher local concentrations of metal ions may cause damage to the tissues, either by direct toxicity or by your body's response as it tries to clear them.

While all types of debris generated by hip implants can cause some reaction in the nearby tissues, in some people it can cause extensive tissue damage including to the muscles, tendons, nerves and bones.

Which hip implants have been recalled?

In 2010, the UK Medicines and Healthcare Regulatory Agency (MHRA) issued three safety alerts, one for all MoM hips and two for ASR (Articular Surface Replacement) hips. The Australian and UK National Joint Registries also reported high failure rates for ASR hip replacements and all large-diameter MoM bearing total hip replacements. DePuy International then recalled all their ASR hip resurfacings and ASR XL total hip replacements.

In 2012, the British Hip Society (BHS) advised against the use of all large-diameter (meaning femoral head diameter of 36mm or above) MoM hip replacements. This advice was largely adopted worldwide. In the same year the MHRA issued a medical device alert on MoM hips that recommended closer follow-up and more investigations for patients with these implants.

In 2015, following a recall by the manufacturer, the MHRA advised against the use of hip resurfacing in all females and for men with femoral head diameters of 47mm or less. The use of hip resurfacing has reduced from a peak of 11% of hips used in the UK in 2008 to less than 1% in 2016.

Anyone who has had an DePuy ASR or ASR XL hip replacement and has any outstanding questions should contact the ASR helpline on 0800 279 4865 or 01908 303195 or go to http://asrrecall.depuy.com/ukpatient

Does this apply to hip-resurfacing and total hip replacement?

Yes, it applies to both types of MoM hip; however, evidence suggests that the problem may be greater for large-diameter MoM total hip replacements.

What is the difference?

A hip resurfacing keeps the ball part of the ball-and-socket hip joint and puts a metal cap over the surface of it. There's also a metal cup on the pelvis side. In a total hip replacement, the ball on top of the thigh bone (the femoral head) is removed and a stem is fixed into the shaft of the thigh bone using either bone cement or uncemented technology (this means the prosthesis is fixed without using cement to 'glue' the implant in). A ball is then fixed onto a spigot on this stem. Both types involve a metal ball rubbing against a metal cup.

How do I know if I have a metal-on-metal hip?

All hip resurfacing operations use MoM bearing hip. Most total hip replacements are not MoM bearings and use other materials including ceramic and high-density polyethylene. Your hospital will always have a record of your operation and what implants were used. You can contact the hospital directly if your operation was done recently and you’re still under the care of the surgeon. Most hospitals will have tried to contact you already if you have a metal-on-metal hip. Otherwise you can contact your GP and they can help put you back in contact.

If you signed a consent form for details of your operation to be sent to the National Joint Registry, you can contact them directly and they can tell you details of your implant. Tel: 0845 345 9991 or email: health_servicedesk@northgate-is.com

If I have a metal-on-metal hip, should I contact my GP or orthopaedic surgeon?

Most hospitals that have put in a number of metal-on-metal hips will have a system to advise patients. You can try contacting them directly, or your GP can help you and refer you to your orthopaedic surgeon.

If you develop pain or start to limp you should tell your doctor straight away, who will arrange for referral or investigations. Another warning sign is a mechanical noise from the joint – grating, grinding, squeaking or clunking. 

Should I be receiving regular check-ups if I have a metal-on-metal hip?

The MHRA recommends follow-up for certain groups of patients. All MoM hips require follow-up for as long as the device is in place. There are two groups that are considered to be at low risk for problems based on current evidence:

  • asymptomatic males with hip resurfacing who have a femoral head diameter of 50mm or greater
  • those with small head diameter (less than 36mm) MoM total hip replacements.

The British Orthopaedic Association recommends follow-up of all hip replacements according to their rating quantified by the Orthopaedic Device Evaluation Panel (ODEP):

  • For implants with an ODEP 10A rating, follow-up should be at 1 and 7 years and then every 3 years.
  • For all others, follow-up should be annually for the first 5 years, then every 2 years until 10 years post-operative, and then every 3 years.

What should these check-ups involve?

Follow-up involves:

  • functional assessment (Oxford hip score) in all cases
  • blood metal ion measurement in most cases
  • MRI or ultrasound in patients with deteriorating function or rising blood metal ion levels.

Functional assessment can be done by a telephone conversation or questionnaire. This will usually be carried out by your surgeon or another healthcare professional from the hospital where you had the surgery.

What will happen if there's damage to the hip?

Not all pains and problems are due to your body's reaction to metal debris. Other causes of pain that can affect all types of hip replacement include loosening, wear and infection. If there's damage to your hip, or a strong likelihood that damage will develop, then you’ll need revision surgery in which the metal-on-metal implants will be removed and new ones inserted. This may also involve fitting a femoral stem to fix the ball onto (in a total hip replacement). If you already have a stem in place and it’s well fixed and undamaged, then this can often be saved. Your surgeon will discuss this with you.

Who regulates the use of hip devices in the UK?

According to the medical device directive of the European Union, the safety and performance of a medical device must be established. For a manufacturer to legally sell a medical device in the European market, the requirements of the directive must be met and a CE mark awarded by a notified body. A notified body is an organisation that has been accredited to assess whether a product meets certain pre-ordained standards.

Once approved for use in the European Union, the UK national regulator takes over the surveillance of the use of the device. The UK regulator is called the Medicines and Healthcare Products Regulatory Agency (MHRA). All failures should be reported to the MHRA.

How would I find out when a type of hip has been recalled?

Medical Device Alerts are the MHRA's way of communicating safety information, including recalls. Alerts are sent out to healthcare professionals and are also published in print and online. The MHRA has an excellent website where you can check for yourself if you’re worried (www.mhra.gov.uk).

Do I need to report any side-effects to the MHRA as well as my doctor?

Anyone can submit a problem with a medical device (such as a hip implant) to the MHRA. This includes clinicians, healthcare workers, carers, patients and members of the public. By law, manufacturers do have to inform the MHRA when they know of failures that have been revised. This, along with NJR data, ensures that the MHRA can keep abreast of problems.

Should I get legal advice if I have a hip that has been recalled?

You should first see your doctor to check if there’s a clinical problem. Your health must come first if there are problems.

With the ASR and ASR XL implants, the manufacturers are – in most cases – paying for all investigations and treatment to put things right. However, these hips are the subject of legal proceedings worldwide so you should get legal advice to see if you're entitled to compensation.

Apart from the recent recall, are there any long-term risks associated with the procedure?

There hasn't been much research done on the long-term effects of these hips on either the tissues around the hip or on tissues elsewhere in the body. There are concerns regarding the high levels of heavy metals (cobalt and chromium) in the blood; however, there are very few reports of actual clinical problems.

Are metal-on-metal implants still being used?

Yes, but only in certain situations. It's the only way to perform a resurfacing operation where the thigh bone is simply capped. The MHRA recommends that only males with a predicted femoral head diameter of 50mm or greater can be considered for hip resurfacing. The 2014 NICE technology appraisal guidance 304 (26th February 2014) recommends that patient activity is considered so that hip resurfacing can be used for those patients who are likely to outlive a conventional primary total hip replacement.

What are the advantages of metal-on-metal hip implants?

It allows hip resurfacing and can allow much larger diameter femoral heads to be used in total hip replacement. Larger heads can also allow a greater range of movement of the hip and give greater stability, making dislocation less likely.

When they're designed and made well, working well, positioned well and lubricated well by joint fluid, MoM implants show some of the lowest wear rates of any materials used in hip replacement. This is what made them so popular. However, if any of these factors aren't right, then the wear can be extremely high and this leads to the problems caused by metal debris.

How do surgeons decide what type and material of hip replacement to use?

Most surgeons find two types of hip replacement that they're happy with. This is usually one for young and active patients and one for the much larger group of older patients (those more likely to need the operation). There are many good hip replacement options that have good follow-up and excellent results published in medical literature.

How can I find out what type and material of hip replacement would be best for me?

Research is constantly being carried out to try to answer this question. All materials have advantages and disadvantages, but most modern materials are showing excellent results and it’s likely that more than one type may be equally effective for you.

How do I make sure I have a good, experienced surgeon?

Your GP is likely to have seen other patients who need hip surgery in your area so they’ll have a very good idea of who to recommend to you. If you have friends, family or other patients who've had hip surgery, they can also give you a 'customer view'.

Where can I get more information?

Your doctor and your surgeon in particular will be able to discuss all matters related to your hip and hip surgery with you. The websites of the British Hip Society and the British Orthopaedic Association will also be helpful. You can also contact the Arthritis Care on freephone 0808 800 4050 or email Helplines@arthritiscare.org.uk for more support.

Hip replacement surgery

Hip replacement

During hip replacement surgery, the surgeon replaces the damaged joint surfaces with artificial parts. It can reduce pain and improve your mobility.

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