What is involved in a knee replacement operation?
The operation usually takes between 1 and 2 hours. The surgeon will make a cut down the front of your knee and then cut away the damaged surfaces of the ends of the thigh bone (femur) and shin bone (tibia) along with a little bit of the underlying bone. The two surfaces that have been removed are then replaced with specially shaped artificial surfaces. The new surface that covers the top of the shin bone (tibia) is usually made of metal and plastic. Sometimes it is only made of metal and a separate piece of plastic is inserted; this is called a mobile-bearing knee replacement. The plastic, whether separate or part of the covering of the shin bone (tibia), allows the two ends of the bones to glide over each other smoothly. Your knee cap (patella) may also be given a new surface, although sometimes it's left alone.
Some surgeons are using minimally invasive techniques - sometimes called keyhole surgery. This means that they make just one or two very small cuts instead of one long cut and use specially designed surgical instruments and telescopes. Your surgeon will discuss with you if this is available.
You will be able to go home once you are eating and drinking normally and are mobile enough to be safe where you are going after you leave hospital.
Are there different types of knee replacements?
Knee replacements can be divided into two types:
Total knee replacement (total knee arthroplasty):
- Most knee replacement operations involve replacing the surface of the bottom end of your thigh bone (femur) and the upper surface of your shin bone (tibia)
- A total knee replacement may also involve replacing your knee cap (patella) with a dome-shaped plastic one.
Unicompartmental (partial) knee replacement:
- If your arthritis only affects one side of your knee (usually the inner side) you may be offered a partial knee replacement.
- A partial knee replacement involves less of your knee being operated on and the recovery is usually quicker.
- It is more likely that a partial knee replacement can be done using minimally invasive techniques.
Whether total or partial, the replacement parts are made of a combination of metal and plastic; the metal parts replace the surfaces of the thigh bone (femur) and shin bone (tibia) and the plastic replaces the meniscus or menisci. (See 'causes' section for more information about the anatomy of the knee joint).
The metal parts may be fixed in place using special cement (cemented) or they may not be fixed (uncemented) but designed so that the your bone grows over them and fixes them in place that way.
Complex or revision knee replacement
This may be needed if arthritis has damaged more than the usual amount of bone or when a previous knee replacement has to be re-done (revised). Sometimes, in very complex situations such as following surgery for bone cancer, the components will be designed specifically to fit in your knee.
Which type should I have?
Your surgeon will discuss this with you. It will depend on how much of your knee is affected by arthritis - it may not be possible to know this until your surgeon has started your operation.
If you have a partial knee replacement it is more likely that you will need to have it done again, than if you have a total knee replacement (TKR). Sometimes the reason for choosing to have a partial knee replacement is that it leaves the option to have a TKR at a later date. However it's also more likely that you will need to have your total knee replacement re-done, if you had a partial knee replacement done before having your total knee replacement.
There are over 150 different designs of knee replacement and some of the differences between all of the different types and makes of knee replacement parts aren't known, particularly how they perform in the long term. In many countries, registries have been set up so that anyone who has had a knee replacement is entered into the register. The information collected is used to monitor how their replacement is performing. In the UK patients also enter information about their health and quality of life before and after their operation.
Did you find this information useful?
- Mini-incision surgery for total knee replacement; NICE Interventional Procedures Guidance, May 2010
- Carr AJ, Robertsson O, Graves S, et al; Knee replacement. Lancet. 2012 Apr 7 379(9823):1331-40. doi: 10.1016/S0140-6736(11)60752-6. Epub 2012 Mar 6.
- Hofstede SN, Nouta KA, Jacobs W, et al; Mobile bearing vs fixed bearing prostheses for posterior cruciate retaining total knee arthroplasty for postoperative functional status in patients with osteoarthritis and rheumatoid arthritis. Cochrane Database Syst Rev. 2015 Feb 4 (2):CD003130. doi: 10.1002/14651858.CD003130.pub3.
- Ferket BS, Feldman Z, Zhou J, et al; Impact of total knee replacement practice: cost effectiveness analysis of data from the Osteoarthritis Initiative. BMJ. 2017 Mar 28 356:j1131. doi: 10.1136/bmj.j1131.
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