The knee is divided into three compartments: the medial (inner), the lateral (outer) and the patello-femoral. Any of these compartments can be replaced, without replacing the entire knee joint.

Knee replacement is sometimes the only surgical option available to patients with knee conditions such as arthritis that cause damage to the knee joint, resulting in problems carrying out everyday activities. The aim of the operation is to relieve pain and improve mobility by replacing the worn-out parts of the arthritic knee with specially designed metal and plastic components.

Most knee replacement surgery is carried out on older people, although it can be offered to patients of any age. In most cases, a replacement knee will last over 20 years.

While knee replacement may be the answer for some people, for others – particularly if you are a younger patient, an athlete, or an older patient who is still very active – removing the knee joint, which also means taking away a great deal of healthy tissue, may not be the best option. In some cases, you may be offered knee realignment surgery (osteotomy) instead; this new procedure can significantly delay, or in some cases even avoid, the need for knee replacement surgery.

You are more likely to need total or partial knee replacement surgery if you have:

• Wear and tear arthritis is by far the most common indication.
• Rheumatoid arthritis
• Psoriatic arthritis
• Haemophilia
• Gout
• Arthritis caused by a previous knee injury
• Deformity of bones in the knee
• Bone death due to poor blood supply (avascular necrosis)

There are two types of knee replacement surgery:

• Total knee replacement (TKR) where both sides of your knee joint are replaced
• Partial (half) knee replacement (PKR) where one part of the joint is replaced

In some cases, your consultant may advise that you have an examination of the knee joint under an anaesthetic using keyhole surgery to decide on the option that is best for you.

Total knee replacement (TKR)

 This operation, first carried out in 1968, is now very common and involves replacing all the surfaces of your worn-out knee with metal and plastic components. It’s offered when lifestyle modifications, painkillers and physiotherapy haven’t relieved your pain or mobility problems.

Damaged cartilage, along with some bone, is removed and replaced with metal parts to form a new joint surface. These are fixed with specially designed cement. The underside of the kneecap is cut and the surface replaced with a plastic component. A spacer is placed between the metal parts to enable the joint to glide smoothly.

More than 90% of people who have TKR surgery have much less knee pain and find it significantly easier to carry out their everyday activities afterwards.

Even with normal use, the replacement knee will eventually wear out but it should last for at 15 if not 20 years. However, putting excessive stress on the new joint can make it loose and painful.

You should be able to walk as much as you want, swim, play golf, drive, cycle, and take part in low-impact sports.

You’ll be advised not to take part in high-impact sports including team sports, running, jogging or jumping for the first 6 months. After this period these activities may put some extra strain on the artificial joint, however, no study has so far shown that there is an increased revision rate in runners. Some patients have returned to ultra-marathons after a knee replacement. Generally, it is considered that joints may wear out due to a combination of activity type, body weight and whether you are an experienced or newly active athlete.

• The time it takes to recover from TKR will depend on may factors including your age, health, severity of initial arthritis and general wellbeing coming into surgery as well as your commitment to follow your rehabilitation programme once you return home after surgery. It is normal to have some pain after surgery and this will gradually reduce with time. Generally, you will be able to do most normal activities between three months and a year before you get back to normal. Papers have reported continual improvement up to 2 years after a knee replacement if targeted exercises continue.
• To achieve the best possible outcome, it’s important to follow your exercise plan which includes gradually increasing walking, and other low-impact exercises. It’s important to avoid falling or injuring your new knee.
• Let your dentist know that you’ve had a knee replacement as you may need to take antibiotics before certain dental procedures to avoid the chance of an infection in the joint, although in most circumstances no additional antibiotic cover is needed.
• It is safe to drive again usually around 4-6 weeks after surgery. However, you should check with your insurance company and ensure you are able to perform all manoeuvres safely.

This operation is offered if only one of the three knee compartments is damaged. In most cases, this is the medial (inner) compartment. As the procedure involves replacing just one part of the knee, the scar tends to be smaller, recovery is faster with less pain, and the range of movement remains better than with a TKR.

A small incision is made and damaged cartilage in one part of the knee, along with some bone, is removed and replaced with metal parts to form a new joint surface.

There is a smaller wound and a shorter procedure than with TKR, meaning a quicker recovery, less blood loss and less pain afterwards. Because much of the knee is preserved, you are likely to retain a greater range of movement than you would after a TKR.

You may need to have total knee replacement surgery in the future if arthritis causes problems in other compartments of the knee. Having said this the outcome of partial knee replacement is very similar to that for total joint surgery.

• The time it takes to recover from PKR is generally slightly shorter than TKR, however, it will depend on many factors including how closely you follow your rehabilitation programme once you return home after surgery.
• You’ll be able to get up and walk shortly after surgery and will be given physiotherapy exercises to carry out at home, but it’s important to avoid falling or injuring your knee.
• You should also let your dentist know that you’ve had a PKR as you may need to take antibiotics before certain dental procedures to avoid the chance of an infection in the joint, although in most circumstances no additional antibiotic cover is needed.
• Most people can get back to their normal everyday activities after about six weeks.
• It is safe to drive again usually around 4-6 weeks after surgery. However, you should check with your insurance company and ensure you are able to perform all manoeuvres safely.

If your previous knee replacement hasn’t been successful, you can have a second procedure where some or all of the artificial components in the knee are replaced with new ones. Problems with previous surgery may be due to wear and tear or loosening of the new knee joint, instability due to ligament damage, stiffness, a fracture or, in some cases, infection.

Revision surgery tends to take longer, and is often more complex, than the original knee replacement, with extensive planning and rehabilitation needed to achieve a good recovery. You will be advised about your surgical options and help you decide which is likely to have the best outcome.