In knee replacement surgery (arthroplasty), a damaged, worn or diseased knee is replaced with an artificial joint.
Knee replacement is a routine operation for knee pain when the knee joint has been severely damaged, most commonly by arthritis.
There are two main types of surgery, depending on the condition of the knee: total knee replacement and partial (half) knee replacement.
More than 70,000 knee replacements are carried out in England and Wales each year, and the number is rising. Most people who have a total knee replacement are over 65, and just over half of all patients are women.
Candidates for knee replacement surgery need to be well enough for both a major operation and the rehabilitation afterwards.
Wear and tear through everyday use means that your replacement knee will not last forever. However, for most people it will last for at least 15-20 years, especially if the new knee is cared for properly and not put under too much strain.
Revision knee replacement surgery (replacing the replacement knee) is usually more complicated and a longer procedure than the original surgery. There is no set limit to the number of times you can have revision surgery, but it is widely accepted that the artificial knee joint becomes less effective each time it is replaced.
Research has also shown that patients become less satisfied with their artificial knee each time it is replaced. This is one reason why knee replacement is less likely to be recommended for younger patients.
Why knee replacement is necessary
Knee replacement surgery (arthroplasty) is usually necessary when a health condition or injury disrupts the normal working of the knee joint so that:
- your mobility is severely reduced
- you experience pain even while resting
How the knee should work
The knee joint acts as a hinge between the bones of the leg. It is really two joints. The major joint is between the thigh bone of the upper leg (femur) and the shin bone of the lower leg (tibia). The smaller joint is between the kneecap (patella) and the upper leg (femur).
A smooth, tough tissue called articular cartilage usually covers the ends of the bones within the knee joint. This protects the ends of the bones and allows them to slide smoothly over each other without pain or too much effort.
The synovial membrane that covers the other surfaces of the knee joint produces synovial fluid, which lubricates the joint, reducing friction to further help movement.
Replacing a damaged knee
Pain and difficulty moving the knee joint are common when the articular cartilage has become damaged or worn away. The ends of the bones start to rub or grind together, instead of smoothly sliding over each other.
Replacing the damaged knee joint with an artificial one can help reduce pain and increase mobility.
The most common reason for knee replacement surgery is osteoarthritis.
Osteoarthritis in the knee occurs when the articular cartilage becomes damaged or wastes away through natural wear and tear. The bones have little or no protection to prevent them rubbing against each other when the knee moves, causing pain.
The bones may compensate by growing thicker and producing bony outgrowths to try to repair themselves, but this can cause more friction and pain. See Osteoarthritis.
Surgical alternatives to a knee replacement
There are alternative surgeries to knee replacement, but results are not as good in the long term.
Arthroscopic washout and debridement
An arthroscope (tiny telescope) is inserted through small incisions in the knee. The knee is washed out with saline and any bits of bone or cartilage are cleared away. It is not recommended if you have severe arthritis.
This is a keyhole (minimally invasive) operation in which small holes are made in the surface layer of bone with a small, sharp ‘pick’. This allows cells from the deeper, more blood-rich bone beneath to come to the surface and stimulate cartilage growth. It can be a good option if you have just a small area of damaged cartilage. However, the benefits are not well proven and the results are not as good as knee replacement for severe arthritis.
This is an open operation in which the surgeon cuts the shin bone and realigns it so that weight is no longer focused on the damaged part of the knee. It is sometimes used for younger people with limited arthritis, where it may enable a knee replacement to be postponed. However, you will usually need a knee replacement at a later date, and the operation may make knee replacement surgery more difficult if it is needed.
Autologous chondrocyte implantation (ACI)
This is when new cartilage from your own cells is grown in a test tube and introduced into the damaged area. It is usually used for accidental injury to the knee rather than arthritis. As yet, ACI is only available as part of a clinical trial.
Mosaicplasty (cartilage replacement)
This is a keyhole (minimally invasive) procedure that involves transferring plugs of hard cartilage, together with some underlying bone from another part of your knee, to repair the damaged surface. Currently, it is only available as part of a clinical trial.
Non-surgical treatment options
Non-surgical options include:
- physiotherapy to improve the flexibility, mobility and strength of your knee joint
- painkillers to reduce pain in your joint so movement is easier
- anti-inflammatory medicines to reduce swelling within the joint, increasing mobility
- steroid injections into your joint to help relieve pain and swelling
- temporarily losing excess weight to reduce the strain on your knees, thereby reducing pain and improving mobility
- using walking aids, such as a cane or crutch
When it should be done
You will normally be offered a knee replacement if you have severe pain, swelling and stiffness in your knee joint and your ability to move the joint is significantly reduced.
A knee replacement is major surgery, so is normally only recommended if non-surgical options have not helped reduce pain or improve mobility.
Knee replacement may be considered for adults of all ages, although young, physically active people are more likely to wear out their replacement joint. As a result, knee replacement is typically recommended for older, less active people as the replacement joint is less likely to wear out and need to be replaced.
Most people who have a total knee replacement are between the ages of 60 and 80. They need to be well enough to cope with both a major operation and the rehabilitation afterwards.
The earlier you have a knee replacement, the greater the chance you will eventually need further surgery. However, there is some evidence that having treatment before the knee becomes very stiff leads to a better surgical outcome.
If you are having a knee replacement because of arthritis and also need a hip replacement, the hip should be replaced first as you will need a flexible hip to do the exercises that are necessary after a knee replacement operation.
You may want to consider surgery if:
- your knee pain is so severe that it interferes with your quality of life and sleep
- medication and other treatment have not worked or cause severe side effects
- everyday tasks, such as shopping or getting out of the bath, are difficult or impossible
- you are feeling depressed because of the pain and lack of mobility
- you cannot work or have a normal social life
Before the operation
What should I look for in a specialist?
Choose a specialist who performs knee replacement regularly and can discuss their results with you.
This is even more important if you are having a second or subsequent knee replacement, known as revision knee replacement, which is more difficult to perform. Look for a specialist who will work with you to find the best treatment.
Your local hospital trust website will show which specialists in your area do knee replacement. Your GP may also be able to recommend someone.
How can I prepare for going into hospital?
- Get informed. Find out as much as you can about what is involved in your operation. Your hospital may provide written information or videos.
- Arrange help. Arrange for a friend or relative to help you at home for a week or two after you come out of hospital.
- Sort out transport. Arrange for someone to take you to and from the hospital.
- Prepare your home. Before you go for your operation, put your TV remote control, radio, telephone, medications, tissues, address book and a glass on a table next to where you will spend most of your time when you come out of hospital.
- Stock up. Buy food that is easy to prepare, such as frozen ready meals, cans and staples such as rice and pasta, or freeze meals and reheat them during your recovery.
- Clean up. Before going into hospital, have a long bath or shower, cut your nails (take off any nail polish) and wash your hair. Put on freshly washed clothes. This helps prevent unwanted bacteria coming into hospital with you and complicating your care.
How can I prepare for the operation?
Stay as active as you can. Strengthening the muscles around your knee will aid your recovery. You can be referred to a physiotherapist, who will give you helpful exercises. If you can, continue to gently exercise, such as walking and swimming, in the weeks and months before your operation.
What will happen before the operation?
A couple of weeks before the operation, you will usually be asked to attend a preoperative assessment clinic to meet your surgeon and other members of the surgical team.
They will take a medical history, examine you and organise any tests (such as blood and urine tests), ECG and X-rays needed to make sure you are healthy enough for an anaesthetic and surgery. They will also give you advice on how to prepare for surgery and will ask you about your home circumstances so your discharge from hospital can be planned. If you live alone, have a carer or feel you need extra support, tell the surgical team so that any help or support can be arranged before you go into hospital.
Take a list or packets of any medication you are taking. Some rheumatoid arthritis medications suppress the immune system, which can affect healing. For this reason, you may be asked to stop taking your medication before surgery. Your surgeon can advise you on alternative medications. There may be leaflets, booklets and videos to look at or take away that can give you more information about the operation.
Use this time before surgery to ask any questions you have.
How it is performed
You will usually be admitted to hospital the day before your operation. The surgeon and anaesthetist will usually come and see you to discuss what will happen. Discuss any anxieties you have with them.
What will happen?
You will not be allowed to eat or drink for approximately six hours before your operation. The ward staff will help you take a bath or shower and put on a surgical gown. You will have to remove make-up, nail polish and jewellery, except wedding rings. If you wear glasses or false teeth, these can be removed in the anaesthetic room. You will then be escorted to theatre by a nurse.
Who will do the operation?
The operation will be performed by a senior-level surgeon, consultant or registrar. They may be helped by junior doctors. You should be told at your preoperative assessment who will be doing the operation. If you are not told, do not be afraid to ask.
How is the operation carried out?
Modern knee replacements involve removing the worn ends of the bones in your knee joint and replacing them with metal and plastic parts (a prosthesis).
You may have either a total or a half-knee replacement. This will depend on how damaged your knee is. Total knee replacements are the most common.
Total knee replacement
In a total knee replacement, both sides of your knee joint are replaced. The procedure takes one to three hours:
- Your surgeon makes a cut down the front of your knee to expose your kneecap. This is then moved to the side so the surgeon can get to the knee joint behind it.
- The damaged ends of your thigh bone (femur) and shin bone (tibia) are carefully cut away. The ends are precisely measured and shaped to fit the appropriately sized prosthetic replacement. A dummy joint is positioned to test that the joint is working properly. Adjustments are made, the bone ends are cleaned, and the final prosthesis is fitted.
- The end of your femur is replaced by a curved piece of metal, and the end of your tibia is replaced by a flat metal plate. These are fixed using special bone ‘cement’, or are treated to encourage your bone to fuse with the replacement parts. A plastic spacer is placed between the pieces of metal. This acts like cartilage, reducing friction as your joint moves.
- The wound is closed with either stitches or clips. A dressing is applied to the wound, and sometimes a splint is used to keep your leg immobile.
- It is long lasting. Typically, a new knee lasts about 15 years.
- It is a tried and tested treatment that has stood the test of time.
- It is a longer operation than partial knee replacement, involving a bigger incision, and more bone needs to be removed.
- A longer hospital stay is necessary and the recovery period is longer.
- A blood transfusion is sometimes needed.
- You may be aware of clicking or clunking in the knee.
- You are still likely to have some difficulty moving, especially bending your knee, and kneeling may be difficult because of the scar.
Partial (half) knee replacement
If only one side of your knee is damaged, you may be able to have a partial (half) knee replacement. This is suitable for around one in four people with osteoarthritis.
- It is a smaller operation, involving a smaller incision, and less bone is removed.
- It requires a shorter hospital stay and recovery period.
- Blood transfusions are rarely needed.
- It results in better movement in the knee, which feels more like a natural knee. You may be able to be more active than after a total knee replacement.
- It is not quite as reliable as a total knee replacement in eliminating pain.
- It does not usually last as long as a total knee replacement, which is likely to mean further surgery is necessary at a later date.
- It is less suitable for a young, active person.
Talk to your surgeon about the type of surgery they intend to use and why they think it is the best choice for you.
If only your kneecap is damaged, an operation called a patellofemoral replacement or patellofemoral joint arthroplasty can be performed. This involves less major surgery with a faster recovery time. However, the long-term results are still unclear and it is not suitable for most people with osteoarthritis.
Mini-incision surgery (MIS)
This new technique can be used for either total or half knee replacements, but is currently more commonly used for half knee replacements.
The surgeon makes a smaller cut over the front of the knee than in standard knee replacement surgery. Specialised instruments are then used to manoeuvre around much of the tissue, rather than cutting through it. This should lead to a quicker recovery.
The National Institute for Health and Clinical Excellence (NICE) has looked at the MIS technique compared with the standard technique for total knee replacements. It compared how well joints from the two different techniques worked and the safety of the patients. From the studies examined so far, the MIS technique may give patients better mobility in the short-term, but the longer-term effects are not yet known. Not many studies on the safety of the MIS technique have been carried out.
NICE has decided that there are still uncertainties about the benefits and risks of this new technique to patients. More information needs to be collected.
If you are considering MIS for your knee replacement, discuss these issues with your doctor. If you do go ahead with it, you may be asked if your details can be used to help gather more information.
The surgeon performs this operation using computerised images, which are generated by attaching infrared beacons to parts of your leg and to the operating tools. These are tracked on infrared cameras in the operating theatre. Results so far suggest that this may enable the new knee joint to be positioned more accurately. Most hospitals do not yet have the equipment to do this and only around 1% of knee replacements are performed in this way.
Risks of surgery
As with any operation, knee replacement surgery has 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.
Your anaesthetist and surgeon can answer any questions you may have about your personal risks from anaesthetic and the surgery itself.
- Infection of the wound. This will usually be treated with antibiotics, but occasionally the wound can become deeply infected and require further surgery. Very occasionally, it requires replacement of the artificial knee joint.
- Fracture in the bone around the artificial joint during or after surgery. Treatment will depend on the location and extent of the fracture.
- Excess bone forming around the artificial knee joint and restricting movement of the knee. Further surgery may be able to remove this and restore movement.
- Excess scar tissue forming and restricting movement of the knee. Further surgery may be able to remove this and restore movement.
- The kneecap becoming dislocated. Surgery can usually repair this.
- Numbness in the area around the wound scar.
- Allergic reaction. You may have an allergic reaction to the bone cement if this is used in your procedure.
- Unexpected bleeding into the knee joint.
- Ligament, artery or nerve damage in the area around the knee joint.
- Blood clots or deep vein thrombosis (DVT). Clots may form in the leg veins as a result of reduced movement in the leg during the first few weeks after surgery. They can be prevented by using special support stockings, starting to walk or exercise soon after surgery, and by using anticoagulant medicines.
In some cases, the new knee joint may not be completely stable and further surgery may be needed to correct it.
Recovering from a knee replacement
In the surgical ward, you may be given a switch that enables you to self-administer painkillers at a safe rate. You may also be given oxygen through a mask or tubes. If necessary, you will be given a blood transfusion.
You will have a large dressing on your knee to protect your wound. Various drains will siphon off blood from the operation site to prevent it collecting inside the wound.
Back in the ward, the team will continue to monitor you carefully. You may be allowed to have a drink about an hour after returning to the ward and, depending on your condition, you will also be allowed to have food. You will need help moving position and using a bed pan.
Your wound dressing will be changed regularly until it has healed over.
How soon will I be up and about?
The staff will help you to get up and walk about as quickly as possible. If you have had minimally invasive surgery, you may be able to walk on the same day as your operation.
Walking with a frame or crutches is encouraged. Most people are able to walk independently with sticks after about a week.
During your stay in hospital, a physiotherapist will teach you exercises to help strengthen your knee. You can usually begin these the day after your operation. It is very important that you follow the physiotherapist’s advice to avoid complications or dislocation of your new joint.
It is normal to experience some initial discomfort while walking and exercising, and your legs and feet may be swollen.
You may be put on a passive motion machine to restore movement in your knee and leg. This support will slowly move your knee while you are in bed. It helps to decrease swelling by keeping your leg raised and helps improve your circulation.
When can I go home?
You will usually be in hospital for 6 to 10 days, depending on what progress you make and what type of knee replacement you have had. Patients who have had a half knee replacement usually have a shorter hospital stay.
If you are generally fit and well, the surgeon may suggest an accelerated rehabilitation programme where you start walking on the day of the operation and are discharged within one to three days.
How will I feel when I get home?
Do not be surprised if you feel very tired at first. You have had a major operation and muscles and tissues surrounding your new knee will take time to heal. Follow the advice of the surgical team and call your GP if you have any particular worries or queries.
You may be eligible for a home help and there may be aids that can help you. You may also want to arrange for someone to help you out for a week or so.
The exercises that your physiotherapist gives you are an important part of your recovery. It is essential that you continue with them once you are at home.
Your rehabilitation will be monitored by a physiotherapist when you attend your appointments at the outpatient physiotherapy department.
You may be given some specific exercises to do. You may also be given advice on taking short walks and carrying out normal household activities, such as walking up and down stairs. These exercises will help restore your movement and strengthen your new knee.
How long will it be before I feel normal?
You should be able to stop using your crutches or walking frame and resume normal leisure activities three to six weeks after surgery. However, it may take up to three months for your pain and swelling to settle down.
Your new knee will continue to recover up to two years after your operation. During this time, scar tissue heals and the muscles are restored by exercise, so it is important to take care and look out for problems such as stiffness, pain or infection.
Even after you have recovered, it is best to avoid extreme movements or sports where there is a risk of falling, such as skiing or riding a bicycle. Your doctor or a physiotherapist can advise you.
When can I drive again?
You can resume driving when you can bend your knee enough to get in and out of a car and control the car properly. This is usually around four to six weeks after your surgery, but check with your physiotherapist or doctor whether it is safe for you to drive.
When can I go back to work?
This depends on your job, but you can usually return to work 6-12 weeks after your operation.
When can I do housework?
For the first three months, you should be able to manage light chores, such as dusting and washing up. Avoid heavy household tasks such as vacuuming and changing the beds. Do not stand for long periods as this may cause ankle swelling and avoid stretching up or bending down for the first six weeks.
How will it affect my sex life?
You may find that having the operation gives your sex life a boost. Your surgeon can advise when you can have sex again. As long as you are careful, it should be fine after six to eight weeks. Avoid vigorous sex and kneeling positions.
Will I have to go back to the hospital?
You will be given an outpatient appointment to check on your progress, usually 6-12 weeks after your knee replacement. The surgeon will want to see you again a year later, and every five years after that to X-ray your knee and make sure it is not beginning to loosen.
Will I need another new knee?
The knee can be replaced as often as necessary, although results tend to be slightly less effective each time. Recovery may take longer, but once you have recovered, the results are usually good.