Metal-on-metal hip replacement Q and A

The answers here are 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.

When they work well, metal-on-metal hip resurfacing and total hip replacements give years of trouble-free use with very low levels of wear. However, some metal-on-metal 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 and loosening of the implants. The National Joint Registry states that 3% of implants loosen after 9 years. However, implants fail for other reasons too, so the overall failure rate is about 1% per year.

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). However, the concentration of metal ions in the fluid around the hip joint can be much higher. It's these high local concentrations of metal ions that cause damage to the tissues, either by local toxicity or by your body's response as it tries to get rid of them.

While all hip debris causes some reaction in the nearby tissues, often with no major problems, in some people it can cause extensive tissue damage and in some rare cases death of tissue cells, including those of the muscles, tendons, nerves and bones.

In 2010, the UK Medicines and Healthcare Regulatory Agency (MHRA) issued three safety alerts, one for all metal-on-metal 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 metal-on-metal bearing total hip replacements. DePuy International then recalled all their ASR hip resurfacings and ASR XL total hip replacements.

The MHRA has advised that all metal-on-metal hips are followed up for 5 years and all ASR / ASR XL hips be followed up for the life of the implant. This is to regularly check how much wear has taken place and therefore how likely you are to need revision surgery. Approximately 100,000 of the ASR hips have been implanted worldwide since 2004 and approximately 10,000 in the UK.

Anyone who has had an DePuy ASR or ASR XL hip replacement and has any outstanding questions should contact the ASR helpline on 0800 2794865 or 01908 303 195.

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

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

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.

All hip resurfacing operations use a metal-on-metal bearing hip. Most total hip replacements are not metal-on-metal 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. Email: enquiries@njrcentre.org.uk

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.

Yes, since the safety alerts and recalls the MHRA are advising that all patients with metal-on-metal hips should be followed up annually for 5 years and that all ASR or ASR XL hips (those models that have been withdrawn) should be followed up for the life of the implant. Patients with hip replacements with head diameter of 36 millimetres or more need to be monitored every year for the life of the hip replacement. Even if you don't need to be formally followed up, if you develop pain or start to limp you should tell your doctor straight away, who will arrange for referral or investigations.

These can take many forms, and if you aren’t having any problems then an annual telephone conversation or questionnaire may be all that's needed. This will usually be carried out by your surgeon or another practitioner from where you had surgery. You’ll need a more detailed assessment if you're in pain, if you have an ASR component or if an x-ray shows signs that the implant has caused problems. This assessment may include physical examination, blood tests to measure the concentration of metal in your blood and possibly ultrasound or MRI examinations.

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 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.

A national regulator called the Medicines and Healthcare Products Regulatory Agency (MHRA) is in charge of classifying medical devices in the UK.

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.

Visit www.gov.uk for more information.

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.

You first need to 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.

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.

Yes. It's the only way to perform a resurfacing operation where the thigh bone is simply capped. There’s some clinical evidence that in younger men (under 55 years) or men who are very active, some metal-on-metal hip resurfacing replacements give equal or slightly better results than total hip replacements. However, overall the use of metal-on-metal hips has reduced very sharply in the last two years.

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, metal-on-metal 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.

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.

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.

Your GP is likely to have seen other patients who need hip surgery in your area so they’ll have a very good idea 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'.

Your doctor and your surgeon in particular will be able to discuss all matters related to your hip and hip surgery with you. The British Hip Society and the British Orthopaedic Association can also be helpful.