In some people, it may be necessary to have surgery to replace a joint that has become severely damaged as a result of AS. The medical term for joint replacement surgery is arthroplasty. The most common types of joint replacement surgery are hip and knee replacement. Other, less common, types of joint replacement include ankle, shoulder and elbow replacement.

Joint replacement should help to:

• Relieve pain
• Improve mobility

There are two main types of hip replacement operation, but a variety of different components and surgical techniques that may be used.

Total hip replacement

In a total hip replacement, part of the thigh bone (femur) including the ball (head of the femur) is removed and a new, artificial ball is securely fixed onto the rest of the thigh bone. The surface of the existing socket in the pelvis (the acetabulum) is roughened to accept a new artificial socket that will join up (articulate) with the ball component.

Many artificial joint components are fixed into the bone with acrylic cement. However, sometimes, especially in more active patients, one part (usually the socket) or both parts may be inserted without cement. If cement is not used, the surfaces of the implants are roughened or specially treated to encourage bone to grow onto them. Bone is a living substance and, as long as it is strong and healthy, it will continue to renew itself over time and provide a long-lasting bond.

The replacement parts can be plastic (polyethylene), metal or ceramic, and are used in different combinations. The harder materials allow better lubrication of the joint, which means that the components should wear more slowly.

• Metal-on-plastic (a metal ball with a plastic socket) is the most widely used combination
• Ceramic-on-plastic (a ceramic ball with a plastic socket) or ceramic-on-ceramic joints are sometimes used in younger, more active patients.
• A metal or ceramic socket is most likely to be used in very active patients. These sockets are thinner than plastic ones, which means that a larger ball component can be used. This gives a greater range of movement and reduces the risk of the dislocation, allowing more vigorous exercise.

Metal-on-metal (MOM) hip resurfacing

With this type of surgery less bone is removed than in a total hip replacement. Instead of removing the head of the thigh bone and replacing it with an artificial ball, a hollow metal cap is fitted over the head of the thigh bone. The socket part of the joint is also resurfaced with a metal component.

People who have this type of operation usually recover more quickly, and the risk of dislocation is lower, allowing the patient to take part in more vigorous sports.

MOM resurfacing isn't suitable for people with low bone density or osteoporosis where the bones are weakened.

Little is known about the long-term performance of these joints as the technique has not been in use for as long as total hip replacements. However, experience so far suggests that resurfacing gives the best results in younger, more active men.

Success of hip replacement surgery

Hip joint replacements are usually very successful operations . How long a new hip joint will last will depend on the type of procedure used and your age and lifestyle, so discuss this with your doctor. You should also discuss how your AS will impact on the time your new hip joint will last. We know that overall, more 8 in 10 of all cemented hips should last for 20 years or longer before a replacement (revision surgery) is needed. However we do not have any figures specifically for hip replacement surgery among people with AS.

The success of surgery will also depend in part on how well you look after your joint. Remember that you will have to exercise your new joint to keep the muscles around it strong, but be very careful not to overstrain your joint.

 When an artificial hip needs to be replaced this is called revision surgery. This type of surgery has made significant advances in recent years. Where revision surgery takes place, more than 8 in 10 of all patients report success for 10 years or more.  Again, these are overall statistics and we don't have the figures specifically for people with AS. The hip can be revised almost as often as needed, although the results are slightly less good each time.

Risks of hip replacement surgery

Joint replacement is major surgery and all major surgery carries risks, which can sometimes be fatal. Risks vary according to your general health and you should discuss the risks and benefits with your surgeon. Although it's important to be aware of the risks, it's also important to keep them in perspective. Many thousands of joint replacements are carried out without complications each year.

When problems with hip replacement surgery do occur, most are treatable. Possible problems include:

Loosening of the joint

The most common problem that can arise with a hip replacement is loosening of the joint. This can be caused by the shaft of the artificial hip becoming loose in the hollow of the thigh bone.  If the loosening is bad, you may need another operation. New developments to improve the outcomes are being developed all the time.

Wear and tear

Some wear and tear can be found in all joint replacements. Too much wear and tear may help cause loosening. In some cases particles that have worn off the artificial joint surfaces can be absorbed by surrounding tissue causing loosening of the joint as bone tends to melt away if this happens.

Infection

Areas in the wound or around the new joint may get infected. To reduce the risk of infection, specially ventilated 'clean air' operating theatres are often used and patients are often given a short course of antibiotics at the time of surgery. 

Minor infections in the wound are usually treated with drugs. Deep infections may need a second operation to treat the infection or replace the joint. It's estimated that a deep infection will only occur in around 1 in 200 patients.

Blood clots

After hip surgery blood clots can sometimes form in the deep veins of the leg. This is called deep vein thrombosis (DVT). Doctors aim to reduce the chances of this happening by using special stockings, medications and exercises. If swelling, redness, or pain occurs in your leg after you leave the hospital, it is very important that you seek medical advice straight away. The danger of DVT is that clots can leave the leg and move into the heart and lungs, which threatens your breathing. It is a rare cause of death after surgery.

Dislocation

In a small number of cases the artificial hip can come out of the socket. It can be replaced under anaesthetic, but repeated problems require further surgery.

Member experience of hip replacement surgery

We have a NASS members experience of hip replacement surgery on the Your stories page if you would like to read a personal account.

In knee replacement surgery, a damaged knee is replaced by an artificial joint. There are two main types of knee surgery:

• Total knee replacement where both sides of your knee are replaced
• Partial (half) knee replacement

It's very important to talk to your surgeon well in advance about the type of surgery they intend to use and why they think it's the best choice for you.

In a total knee replacement, both sides of your knee joint are replaced. The procedure takes 1-3 hours.

The advantages of a total knee replacement are that it is long lasting, typically lasting about 15 years, and that it's a tried and tested treatment that has stood the test of time.

The disadvantages are that it's a longer and more invasive operation than partial knee replacement, meaning a longer stay in hospital and a longer recovery time. A blood transfusion is sometimes needed. Afterwards you may be aware of some clunking or clicking in the knee and you are likely to still have some difficulty moving, especially when bending your knee.

If only one side of your knee is damaged your surgeon may think you could have a partial knee replacement. This is a smaller, less invasive operation, requiring a shorter hospital stay and recovery time. Blood transfusions are very rarely needed. This type of surgery results in better movement in the knee so it feels more like a natural knee.

On the downside, partial knee replacement is not quite as reliable as a total knee replacement in eliminating pain. It also doesn't usually last as long as a total knee replacement.

As with any surgery, knee replacement carries risks as well as benefits. Most people who have a knee replacement have no problems at all. Complications occur in about 1 in 20 cases, but most of these are minor and can be successfully treated.

Risks include:

• Infection of the wound
• Fracture in the bone around the artificial joint during or after surgery
• Excess bone forming around the artificial knee joint and restricting movement of the knee
• Excess scar tissue forming and restricting movement of the knee
• Dislocation of kneecap
• Allergic reaction to the bone cement
• Unexpected bleeding into the knee joint
• Ligament, artery or nerve damage around the knee joint
• Blood clots or deep vein thrombosis