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Arthritis health centre

Knee RA (rheumatoid arthritis of the knee)

Rheumatoid arthritis is a serious type of inflammatory arthritis that affects over 580,000 people in England and Wales according to the NHS. RA affects more women than men. RA can affect people of any age, even very young children.

Unlike osteoarthritis (OA), the "wear-and-tear" arthritis, RA is a chronic autoimmune disease. RA usually occurs in a symmetrical pattern, affecting the hands, knees, ankles, feet, hips, elbows or shoulders on both sides of the body.

RA causes severe joint swelling, joint pain, stiffness and deformity. It can also affect other tissues and organs such as the heart, skin and lungs. RA can also cause fever, fatigue, weight loss and flu-like symptoms.

Getting dressed, tying shoelaces or walking to the car may be painful with knee arthritis. However, with early and aggressive medical treatment, most cases of knee RA can be managed.

What is knee RA?

Rheumatoid arthritis of the knee causes the joints to become tender, warm and swollen. Although knee osteoarthritis causes pain and stiffness, joint pain with knee RA is usually more severe.

Normally, a small pouch covered with a thin tissue called synovium lies between the two pieces of joint cartilage. Cartilage is a material that covers the ends of joint bones. Cartilage helps to keep bones from rubbing against each other during movement.

The synovium secretes a liquid. This liquid helps keep joints lubricated. When joints are well lubricated, they move smoothly and painlessly. Inflammation of the synovium leads to damage and permanent destruction of the joint.

What are the signs and symptoms of knee RA?

With knee RA, you may feel the following:

  • Pain
  • Swelling, inflammation
  • Stiffness
  • Warmth around the knee joints
  • Fever
  • Flu-like symptoms
  • Fatigue


What causes knee RA?

The actual causes of RA are not understood. We know that RA occurs when the body's immune system doesn't function properly.

RA may be linked to genetics. Environmental factors also may be involved, but experts are unsure of the exact cause.

How is knee RA diagnosed?

Your GP can diagnose knee RA. He or she will do a physical examination, talk to you about your personal and family medical history and arrange blood tests.

  • Blood tests for RA may be positive for the following:
  • Anaemia (low red blood cell count)
  • Rheumatoid factor (RF), found in about 70% to 80% of those with RA
  • High erythrocyte sedimentation rate (ESR), which indicates inflammation
  • Antibodies to cyclic citrullinated peptides (CCP)
  • High levels of C-reactive protein (CRP)

Your doctor may order an X-ray of the joints. An MRI scan may also be used to detect evidence of joint damage or destruction.

You may have a sample of joint fluid (synovial fluid) taken to analyse. People with RA usually have joint fluid that's filled with inflammatory material.

WebMD Medical Reference

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