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As with any operation, knee replacement surgery has risks as well as benefits. Most people who have a knee replacement do not experience serious complications.
Your anaesthetist and surgeon can answer questions you may have about your personal risks from anaesthetic or the surgery itself.
Complications occur in about one in 20 cases, but most are minor and can be successfully treated. Possible complications include:
In some cases, the new knee joint may not be completely stable and further surgery may be needed to correct it.
Wear and tear through everyday use means your replacement knee will not last forever. However, for most people it will last at least 15-20 years, especially if 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 the artificial knee joint becomes less effective each time it is replaced.
Knee replacement surgery (arthroplasty) is usually necessary when the knee joint is worn or damaged to the extent that your mobility is reduced and you experience pain even while resting.
The knee joint acts as a hinge between the bones of the leg and is effectively 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 covers the ends of the bones, allowing them to slide smoothly over each other. The synovial membrane that covers the other surfaces of the knee joint produces synovial fluid, which lubricates the joint, reducing friction.
If the articular cartilage becomes damaged or worn, the ends of the bones rub or grind together, causing pain and difficulty moving the knee joint.
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 through natural wear and tear. The bones have little or no protection to prevent them rubbing against each other when the knee moves.
The bones may compensate by growing thicker and producing bony outgrowths to try to repair themselves, but this can cause more friction and pain.
Other conditions that may make knee replacement necessary include:
You may be offered knee replacement surgery if:
Read information about how knee replacement surgery is performed.
There are alternative surgeries to knee replacement, but results are often not as good in the long term. These are described below.
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.
A keyhole 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.
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.
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.
A keyhole operation that involves transferring plugs of hard cartilage, together with some underlying bone from another part of your knee, to repair the damaged surface.
You will usually be admitted to hospital on the day of your operation. The surgeon and anaesthetist will usually come and see you to discuss what will happen and answer any questions you have.
A senior-level surgeon, consultant or registrar will perform surgery. 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.
Knee replacement surgery is usually performed either under general anaesthetic (you are asleep throughout the procedure) or under spinal or epidural anaesthetic (you are awake but have no feeling from the waist down).
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 (see below). This will depend on how damaged your knee is. Total knee replacements are the most common.
Read more information about what happens on the day of your operation.
In a total knee replacement (TKR), both sides of your knee joint are replaced. The procedure takes one to three hours:
Total knee replacement is a common procedure and the replacement should last around 15-20 years.
However, you are still likely to have some difficulty moving, especially bending your knee, and kneeling may be difficult because of the scar.
Read more information about recovering from knee replacement surgery.
If only one side of your knee is damaged, you may be able to have a partial (half) knee replacement (PKR). PKR is a smaller operation, which uses a smaller incision, and involves less bone being removed. It is suitable for around one in four people with osteoarthritis.
There are advantages to PKR including a shorter hospital stay and recovery period. Blood transfusions are also rarely needed. PKR often results in more natural movement in the knee and you may be able to be more active than after a total knee replacement.
However, PKR does not always ease pain as well as a total knee replacement and it does not usually last as long, which is likely to mean further surgery at a later date. It is also 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.
In some cases, there may be other types of procedure used. These are described below.
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.
It 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 the tissue, rather than cutting through it. This should lead to a quicker recovery.
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.
This is a more recent advance in knee replacement surgery. A patient-specific alignment guide is created using magnetic resonance imaging (MRI) scans. This helps to create the best fitting technique for each individual patient's implant.
The potential advantage of this procedure is that the implant may last longer due to the most accurate fitting possible. However, as this is a new technique the results and the long term effects are not fully known yet.
Recovery times can vary depending on the individual and type of surgery carried out. It is important to follow advice the hospital gives you on looking after your knee.
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 syphon off blood from the operation site to prevent it collecting inside the wound.
Your wound dressing will be changed regularly until it has healed over.
Read more information about what happens after an operation.
The staff will help you to get up and walk about as quickly as possible. If you have had minimally invasive surgery or are on an enhanced recovery programme, 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 but this can vary depending on the individual.
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 important to follow the physiotherapist's advice to avoid complications or dislocation of your new joint.
It is normal to experience 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.
You will usually be in hospital for six to 10 days, depending on what progress you make and what type of knee replacement you have. Patients who have a half knee replacement usually have a shorter hospital stay.
If you are generally fit and well, the surgeon may suggest an enhanced recovery programme where you start walking on the day of the operation and are discharged within one to three days.
Read more information about getting back to normal after an operation.
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 doctor 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 your physiotherapist gives you are an important part of your recovery. It is essential you continue with them once you are at home. Your rehabilitation will be monitored by a physiotherapist.
You should be able to stop using crutches or walking frame and resume normal leisure activities three to six weeks after surgery. However, it may take up to three months for 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 will heal and muscles will be restored by exercise.
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.
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.
This depends on your job, but you can usually return to work six to 12 weeks after your operation.
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.
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.
You will be given an outpatient appointment to check on your progress, usually six to 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.
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, results are usually good.
Knee replacement surgery (arthroplasty) involves replacing a damaged, worn or diseased knee with an artificial joint.
It's a routine operation for knee pain most commonly caused by arthritis.
Most people who have a total knee replacement are over 65.
For most people, a replacement knee will last for at least 15 to 20 years, especially if the new knee is cared for properly and not put under too much strain.
There are two main types of surgery, depending on the condition of the knee:
Learn more in how knee replacement surgery is performed.
The most common reason for knee replacement surgery is osteoarthritis. Other conditions that cause knee damage include:
A knee replacement is major surgery, so is normally only recommended if other treatments, such as physiotherapy or steroid injections, haven't helped reduce pain or improve mobility.
You may be offered knee replacement surgery if:
Learn more in why knee replacement surgery is used.
Adults of any age can be considered for a knee replacement, although it's typically recommended for older people as young, physically active people are more likely to wear the joint out.
The earlier you have a knee replacement, the greater the chance you will eventually need further surgery. However, there is some evidence that replacing the knee joint before it becomes very stiff leads to a better outcome.
Most total knee replacements are carried out on people between the ages of 60 and 80. You will need to be well enough to cope with both a major operation and the rehabilitation afterwards. Read more about getting ready for knee replacement surgery and recovering from knee replacement surgery.
Knee replacement surgery is a common operation and most people do not experience complications. However, as with any operation, there are risks as well as benefits.
Complications are rare but can include:
In some cases, the new knee joint may not be completely stable and further surgery may be needed to correct it.
Read more about the risks of knee replacement surgery.
Janet Collins has had both her knees replaced and can walk much better than before.
“I have severe arthritis and had been in a lot of pain with my knees for some time. They were very swollen too. I went to the hospital and had an X-ray and the doctor suggested a knee replacement.
"I had my left knee done in 2002 and my right in 2004. I was quite nervous before the first operation, but the consultant came down to greet me and held my hand. The operation went well and the next day the physiotherapist helped me to lift my leg up and bend it slightly. After that, I got up and had a walking frame. I was out of hospital within a week. The operation affected my sciatic nerve, which was very painful at first, but it gradually got better.
“When I had my right knee done, I was in hospital for three weeks because doctors thought I had a blood clot. Thankfully I didn’t. Since then I haven’t looked back. I'm disabled and use a wheelchair or scooter, but I am much more able to go about with just my sticks, whereas before I would have used a frame.
“I can’t kneel on the bed or the floor because it feels strange. They do click, but you get used to that. I exercise for five minutes every morning and evening. I would say my knees are 100% better than they were before. I would recommend the operation to anyone.”
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.
Your local hospital trust website will show which specialists in your area do knee replacement. Your doctor may also have a recommendation, or arrange for you to follow an enhanced recovery programme.
Read more information about preparing for surgery.
Stay as active as you can. Strengthening the muscles around your knee will aid your recovery.
If you can, continue to take gentle exercise, such as walking and swimming, in the weeks and months before your operation.You can be referred to a physiotherapist, who will give you helpful exercises.
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 tests and urine tests), ECGs (electrocardiograms) and X-rays needed to make sure you are healthy enough for an anaesthetic and surgery.
Take a list 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 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.
Read more information about seeing a specialist before an operation.
Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.