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How it is performed
View original article on NHS Choices
You'll 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.
Most people would have seen their surgeon at a pre-assessment clinic and had the chance to the operation.
A senior-level surgeon, consultant or registrar will do the operation. They may be helped by junior doctors. You should be told at your pre-operative assessment who will be doing the operation. Ask if you're not told.
How the operation is done
Knee replacement surgery is usually performed either under general anaesthetic (you're asleep throughout the procedure) or under spinal anaesthetic or epidural (you're awake but have no feeling from the waist down).
The worn ends of the bones in your knee joint are removed and replaced with metal and plastic parts (a prosthesis) which have been measured to fit.
You may have either a total or a partial knee replacement. 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.
Total knee replacement
In a total knee replacement, both sides of your knee joint are replaced. The procedure takes 1 to 3 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 and shin bone are cut away. The ends are precisely measured and shaped to fit the 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 thigh bone is replaced by a curved piece of metal, and the end of your shin bone 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 back of the knee cap may also be replaced, depending on the reasons for replacement.
- The wound is closed with either stitches or clips and a dressing is applied to the wound. In rare cases a splint is used to keep your leg immobile, but you're usually encouraged to move your knee as early as possible.
You're likely to still have some difficulty moving after your operation, especially bending your knee. 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 knee replacement. This is a simpler operation, which involves a smaller cut and less bone being removed. It's suitable for around 1 in 4 people with osteoarthritis.
The advantages of partial knee replacement include a shorter hospital stay and recovery period. Blood transfusions are also rarely needed. This type of joint replacement often results in more natural movement in the knee and you may be able to be more active than after a total knee replacement.
Talk to your surgeon about the type of surgery they intend to use and why they think it's the best choice for you.
In some cases, there may be other types of surgery you can have, including:
If only your kneecap is damaged, an operation called a patellofemoral replacement or patellofemoral joint arthroplasty can be performed. This is a simpler surgery with a faster recovery time. However, the long-term results are still unclear and it's not suitable for most people with osteoarthritis.
This is usually used for partial knee replacements.
The surgeon makes a smaller cut 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.
Read the NICE guidance on mini-incision surgery for total knee replacement.
The surgeon performs this operation using computerised images, which are generated by attaching infrared beacons to parts of your leg and to the operating instruments. 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 don't yet have the equipment to do this and only around 1 in 100 knee replacements are performed in this way.
Patient-specific knee replacement
This is a more recent advance in knee replacement surgery. A guide is created using MRI scans. This helps to create the best fitting prosthesis for each patient.
The potential advantage is that the prosthesis may last longer, as the most accurate fitting is used. However, as this is a new technique, the results and long-term effects aren't fully known yet.