The different types of hip replacement: your options

The options: how do you decide which hip replacement to have?

The first thing to decide is whether you need a traditional Total Hip Replacement (THR) or whether you might be a candidate for resurfacing, a relatively new operation that emerged in the mid 1990s.

There are many different types of hip replacement. But fortunately it isn’t up to you to pick one out of the nearly 100 on the market. Your surgeon will, with their experience, know which model is best for your situation. As well as the exact model of hip replacement, you and your surgeon will need to discuss which type of replacement would be best for you.

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Choosing the right hip replacement

There are many different types of hip replacement. But fortunately it isn’t up to you to pick one out of the nearly 100 on the market. Your surgeon will, with their experience, know which model is best for your situation.

As well as the exact model of hip replacement, you and your surgeon will need to discuss which type of replacement would be best for you.

Most hip replacements are total hip replacements (THR). With this operation the surgeon will remove part of the femur (thigh bone), and the ball-shaped part at the top of the bone (the head of the femur).

They will then fit an artificial ball, smaller than the original one, to the rest of the thighbone. The surgeon then roughens up the inner surface of the socket into which the new ball joint will be fitted. This is so that the artificial socket can be fitted securely in place. The artificial ball and socket should then work together in the same way as the natural hip-and-thigh joint does.

Often the two parts of the joint are attached to the bone socket with acrylic (a special form of plastic) cement. However, a different technique is becoming more popular, especially for people who lead active lives. Rather than using cement, the surgeon roughens or uses a special treatment on the surfaces of the implants. This helps bone to grow onto and bond with them. If only one part of the new joint is fixed using cement it’s known as a hybrid hip replacement.

The replacement parts for your hip would usually be made of metal, plastic or ceramic. These are used in a variety of combinations, but a metal ball fitting into a plastic socket – metal-on-plastic - is the most common. A metal ball with a metal socket is used sometimes, usually in people who are younger and more active. However, there are concerns about the use of metal on metal MoM replacements, which are now subject to updated guidelines.

Total hip replacement (THR)

A total hip replacement is what most people will end up with, but there are still myriad options.

In a THR, the surgeon is essentially replacing the hip's natural ball and socket joint with an artificial one. First he removes the top part of the thigh bone (femur) and inserts a long shaft with a ball at the top end. He then hollows out the hip socket and puts in an artificial socket. The two parts – the ball and socket – then slot in to each other.

For a start, there are many types of artificial joints (prostheses), which vary in shape and design (the most common are the Charnley and Exeter hips), and also in material, which can be plastic, ceramic or metal. A study carried out on hip replacement implants found that for older people there was no evidence that newer and more expensive implants would be better. For those under 65 there was a possibility that a more recently designed type of implant could be more cost-effective.

The most widely used combination is a metal ball with a plastic socket (doctors call this “metal-on-plastic”).

Increasing numbers of surgeons, especially in private hospitals, are using cementless THRs, where the bone grows into the replacement parts, or a ‘hybrid’, where one part is cemented in but not the other.

Whether to use cement to fix the hip replacement

The next decision is whether to use cement to fix the replacement parts in place. A THR with cement is the traditional choice, and still the most popular; it accounts for 50% of all hip operations.

In a cementless THR, the surface of the replacement part is roughed up and sometimes a coating is applied to encourage the bone to grow through it, but no adhesive is used.

The surgeon needs to hammer the new joint in place very firmly. Non-cemented hips are thought to last longer, but the downside is that it is more difficult to remove the new joint if there is a problem.

As research has shown that orthopaedic surgeons who do the most operations of a particular type get the best results, it's often best to stick with their recommendation.

“We do get patients who have read about the latest developments on the Internet and want to find out more, which is fine,” says John Hodgkinson, consultant orthopaedic surgeon at the Wrightington Hospital, where Sir John Charnley pioneered total hip replacements in 1962.

“There are theoretical advantages and disadvantages for all of the options. For example, with a plastic socket, you get tiny fragments of plastic collecting around the hip joint in a kind of sludge. But with metal, although it is harder and will theoretically last longer, there is the risk of tiny metal particles entering the bloodstream. Patients can look on the internet and find evidence to support any position.”

Like Mr Hodgkinson, the Government's National Institute for Health and Clinical Excellence is a fan of the THR with cement because it is the tried and tested option.

Its guidance says doctors should choose a hip that has been proved to last more than 10 years, and if they opt for a newer type, it should have three years’ evidence and be on target to meet the 10-year benchmark.

There is now a National Joint Registry, set up to collect data on all hip (and knee) replacements in England and Wales, in both NHS and independent hospitals.

You can download the NJR’s annual report at www.njrcentre.org.uk, for information on prostheses used, techniques and outcomes.

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Are you eligible for resurfacing?

Resurfacing now accounts for 5-10% of all hip operations, although it's usually only offered to younger patients. Because there is less risk of dislocating a resurfaced hip, it can be useful for those who still want to do sports like skiing and mountaineering.

With resurfacing, the surgeon doesn't need to remove as much of the thigh bone. Instead he fits a metal cap over the top of the bone and resurfaces the hip socket with metal, so the two parts move together.

“Resurfacing is only really suitable for younger patients, generally women aged up to 55 or 60, and men aged up to 60 or 65,” says Graham Keene, consultant orthopaedic surgeon at BUPA Cambridge Lea Hospital.

“As we get older, our bones become weaker and the risk of a fracture with resurfacing is thought to be too high.”

Resurfacing is just as major an operation as a total replacement, and recovery times are similar.

Doctors agree not enough is known about the side effects of resurfacing, which include the theoretical risk of metal contamination. 

What is metal-on-metal hip resurfacing?

This is a different approach to hip replacement. In this case instead of removing the top section of the thighbone surgeons fit a hollow metal cap over the head of the thighbone. They also resurface the socket part of the joint with metal.

The advantage of this type of implant (known as MoM) has been that your risk of having a dislocated hip is lower, and if you enjoy sports and exercise you may be able to carry on with these (but this isn’t guaranteed). However this type of resurfacing isn’t appropriate for people who have low bone density, or whose bones are weakened because of osteoporosis, as you may have read in the news. It has also come under increasing scrutiny because of other health issues.

Metal-on-metal (MoM) hip implants have caused some concern over recent years. The Medicines and Healthcare products Regulatory Agency (MHRA), is the body that regulates medicines and medical devices in the UK. In the past it has published guidance to healthcare professionals working with patients who have had MoM hip implants. This guidance was to make sure that the 56,000* people in the UK who have had these implants are monitored for known problems.

Following further concerns about this type of implant, in June 2017 the MHRA published updated guidance for doctors and healthcare professionals involved with patients who have had MoM hip replacements. This guidance includes:

• Putting updated systems in place for following-up and investigating all patients who have had MoM hip replacements.
• Giving more weight to the results of MARS, MI or ultrasound scans than to isolated blood metal levels alone, when making treatment decisions.
• Rising blood metal levels may be a sign that there may be a reaction in the patient’s soft tissue in the future.
• After revision surgery to a patient’s hip doctors would expect to see a drop in the levels of chromium and/or cobalt, and an improvement in the patient’s symptoms.
• If the symptoms persist your surgeon or doctor should carry out further investigation for possible causes. These can include loosening of the components, instability and infection.
• Any decisions to make a revision to a patient’s replacement hip will take into account the patient in the case, the implant type and positioning, and their blood metal levels.

Phillipa Williams, Head of Communications at Arthritis Research UK, comments:

‘Joint replacements are a key treatment for people with osteoarthritis, offering a lifeline to millions of people who are living in pain every day. But they are not perfect, do not last forever and success is not guaranteed’ she explains.

‘A small percentage of all hip replacements in the UK are metal-on-metal and in some cases, these replacements can fail. As part of their standard process, the Medicines and Healthcare products Regulatory Agency (MHRA) have reissued their advice encouraging all healthcare professionals to contact patients for a review.

The advice for people with joint replacements has not changed. If you are in pain or experiencing symptoms that could relate to joint replacement surgery, we advise that you contact your surgeon.”

Potential problems caused by metal-on-metal implants

These problems can include the failure of some of these implants, which means they are subjected to higher levels of wear.

When this happens it tends to create debris made up of particles (ions) of the cobalt and chromium that are in the implant. In most cases these ions end up in your bloodstream, and eventually pass through your kidneys and out of your body in your urine.

Your body can react to high concentrations of these ions, particularly if they are at high levels in one area – around your hip, for instance. This reaction can mean that the bone around your implant can wear away, and muscles, tendons and nerves around your hip can be damaged, with the result that the implant may become loose and unstable.

In the National Joint Registry’s annual report (published in 2016), it states that 17.65% of MoM hip implants fail after 10 years. This is about three times more often than with other types of replacement hip.

Articular Surface Replacement (ASR) hips are more likely to be affected than other types. And they are more likely to have problems when the smaller sizes are used, and when they are fitted in women. (These have now been recalled by their manufacturer, so are no longer available for implantation.)

These implants have been found to wear down more quickly in some patients. This may cause damage to the bone and inflammation in the tissues nearby.

Another concern is that traces of metal from the worn implants could get into the blood stream. This is known as debris, and consists of ions (particles) of the metals cobalt and chromium that are used to make your hip implant. This can cause inflammation in some people. However, this doesn’t apply to all metal-on-metal replacements, only those with a large head. (These are often known as large head metal-on-metal.) The MHRA has stated that anyone with this type of implant should be monitored and have blood tests as long as the implant is in place.

In 2015 the Medicines and Healthcare products Regulatory Agency (MHRA) advised that hip resurfacing shouldn’t be carried out on any women, or on men who have femoral head (the highest part of your upper leg bone) diameters of 47mm, or less than this.

If you are concerned about your hip replacement, or have pain in your groin, hip or leg, swelling in the area, grinding in the joint, problems walking and changes to your general health, you should see your doctor, or contact the surgeon who carried out the operation.

Symptoms to watch out for after metal-on-metal hip replacement

The friction that’s caused when two metal surfaces move against each other, as happens in MoM implants, can create ions, the miniscule metal particles that can come away from the main part of the metal surface of your hip implants, through wear.

These don’t always cause problems, but in some people they can cause inflammation – and pain – in the immediate area. In some cases this can lead to bone erosion in the area, which can then lead to your hip implants becoming looser, and as a result, less reliably stable.

According to the National Joint Registry around 3% of hip implants tend to become looser after nine years. When added to other causes of failure, this means that about 1% of hip implants fail each year.

It’s helpful to know exactly what to watch out for. Symptoms can include:

• swelling around your hip joint
• feelings of grinding in your hip joint
• pain, (which can be in the joint itself), and in your hip, or the affected leg

The debris in your body that comes from a hip replacement doesn’t usually cause sudden serious problems, however some people can have more extreme reactions, such as tissue damage.

It’s important to pay attention to your general health. While the link to your hip replacement may not seem obvious, you should see your doctor if you have symptoms such as:

• gaining weight
• feeling cold more often than usual
• finding it harder to breath and having chest pain

If the friction in your hip joint continues for some time, it can have more serious effects on the joint and the area around it. This can include damage to the hip bones and joint and the immediate area around the joint. If this problem carries on, your hip implant may become unstable, and painful. At this point you may need to have an operation to repair the damage and prevent further pain.

If you are having symptoms that you feel may be related to your MoM hip replacement – pain in your hip for instance - or are concerned that it may be causing damage that you aren’t aware of yet, contact the surgeon who carried out your operation.

You should be able to contact your surgeon through the hospital where your operation was carried out, or directly, at their practice or office. Anyone who has had a hip replacement where the ‘head’ of the artificial hip measures 36 millimetres or more, should be checked every year that this artificial hip is in place.

Finding the right surgeon

It’s important to have your operation carried out by an experienced surgeon – someone who has performed the operation many times before, and has expertise in this area. They will talk through the options open to you, regarding your hip operation.

It’s important that you and your surgeon talk about what you are hoping for from the operation. Are you happy gardening, and taking gentle walks, or do you plan to run a marathon? Let your surgeon know what you’d like to be doing once you’ve recovered from the operation.

If you have had a hip replacement, or are going to have one, you can find out more about the surgeon who is going to, carry out your operation by going to: surgeonprofile.njrcentre.org.uk/

Recovering well from hip surgery

Useful websites

Versus Arthritis - www.versusarthritis.org/
National Joint Registry for England and Wales - www.njrcentre.org.uk
NHS Choices - www.nhs.uk

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