Knee Replacement - Causes

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.

Cross-section of a normal knee joint

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

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:

  • Haemophilia.
  • Sero-negative arthritis.
  • Avascular necrosis.
  • Gout.

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Dr Jacqueline Payne
Peer Reviewer:
Dr Helen Huins
Document ID:
29427 (v1)
Last Checked:
04 July 2017
Next Review:
03 July 2020

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. Patient Platform Limited has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.