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Other types of knee arthritis


Osteoarthritis is a joint disease caused by "wear and tear." In osteoarthritis, cartilage in the joint breaks down and wears away. As a result, the bones rub together, causing pain, swelling, and stiffness.

Osteoarthritis (OA) is by far the most common cause of knee arthritis. However, other types of arthritis may cause knee pain.

Rheumatoid arthritis

Rheumatoid arthritis (RA) is a long-term disease that causes inflammation of the joints and surrounding tissues. It can also affect other organs.

The exact cause of RA is unknown. It is an autoimmune disease. An autoimmune disease occurs when the body's immune system mistakes healthy tissue for foreign substances. As a result, the body attacks itself, causing symptoms such as joint swelling. Infection, genetic make-up, and hormones also may help cause the disease.

RA often affects joints on both sides of the body equally. It often occurs in both wrists, fingers, knees, feet, and ankles. The course and the severity of the illness can vary. Most RA patients have very swollen joints.

Reactive arthritis

Reactive arthritis is a group of conditions that causes inflammation in the joints, urethra, and eyes. There also may be sores (lesions) on the skin and mucous membranes.

The exact cause of reactive arthritis is unknown. It may follow bacterial infections such as chlamydia, campylobacter, salmonella, or yersinia. Your genetic make-up may make you more prone to reactive arthritis.

Urinary or gastrointestinal symptoms usually appear within days or weeks of an infection. Low-grade fever, inflammation of the conjunctiva of the eye (conjunctivitis), and arthritis develop over the next several weeks.

It happens most commonly in men before the age of 40. Reactive arthritis is rare in younger children but may occur in adolescents. In most people, reactive arthritis goes away in about 12 months.

Psoriatic arthritis

Psoriatic arthritis is a condition that affects some people with psoriasis of the skin. The arthritis may be mild and occur in only a few joints, such as those at the end of the fingers or toes. In some people, the disease may be severe and affect many joints, including the spine. When psoriatic arthritis occurs in the spine, the symptoms are stiffness, burning, and pain, most often in the lower spine and sacrum (part of the tail bone).

People who also have psoriatic arthritis usually have the skin and nail changes that occur in psoriasis. Often, your skin will get worse at the same time as your arthritis.

Infection in the knee joint

Septic arthritis (infection in the knee joint) is inflammation of a joint due to an infection. The infection can be caused by one or many different types of bacteria or fungus. Septic arthritis can develop when the infection spreads through the bloodstream to a joint. It may also occur when the joint is infected with bacteria due to an injury or during surgery. These infections need to be taken care of urgently. Please make sure your doctor know about your symptoms. The most common sites for this type of infection are the knee and hip.

People with artificial knee joints are also at risk for infections. Symptoms may include:

  • Bone pain
  • Fever and chills, along with sweating
  • General discomfort, uneasiness, or ill-feeling (malaise)
  • Swelling, redness, and warmth in or near the knee joint
  • Nausea
  • Difficulty walking because of increased pain in the joint
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Review Date: 8/9/2018

Reviewed By: C. Benjamin Ma, MD, Professor, Chief, Sports Medicine and Shoulder Service, UCSF Department of Orthopaedic Surgery, San Francisco, CA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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