What is the knee joint?
There are four bones around the area of the knee joint: the thigh bone (femur), the main shin bone (tibia), the outer shin bone (fibula) and the kneecap (patella). The main movements of the knee joint are between the femur, the tibia and the patella.
Each knee joint also contains an inner and outer meniscus (a medial and lateral meniscus). The menisci (plural of meniscus) are thick rubbery pads of cartilage tissue. The menisci act like shock absorbers to absorb the impact of the upper leg on the lower leg. They also help to make the knee movements smooth and help to make the knee stable.
Your knee doesn't just bend and straighten like a hinge: just before you fully straighten your knee, there is a little twist of your thigh bone (femur) onto your shin bone (tibia).
What are the main causes of needing a knee replacement?
The main reason for needing to have a knee replacement is arthritis in your knee:
Osteoarthritis (OA) of the knee is the most common reason for a knee replacement. It can be primary or secondary:
- Primary osteoarthritis:
- Is not caused by previous damage or injury to the joint.
- It is more common in people who have a close relative, particularly a brother or sister, with osteoarthritis.
- It is more common as you get older and in people who are obese.
- Secondary osteoarthritis:
Rheumatoid arthritis (RA) is a less common cause and knee replacements for this reason are reducing. This is because the treatments for rheumatoid arthritis have improved.
Any condition that can cause damage to the cartilage of the knee might result in needing a knee replacement, such as:
- Sero-negative arthritis.
- Avascular necrosis.
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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