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Number of total knee replacements performed in the United States - primarily for arthritis - according to the American Academy of Orthopaedic Surgeons, in 2004.
*Source: Centers for Disease Control and Prevention

Knee Arthritis Overview

Arthritis is a general term that describes inflammation and deterioration in joints. It results from damage to the coating or gliding surface in the knee called the articular cartilage.

Knee arthritis can make ordinary activities like walking and climbing stairs difficult and painful. Damage from arthritis to the knee joint cartilage and underlying bone might also result in deformities, such as knock-knee or bow-legs, and unusual knee sounds, called crepitus, might become more obvious.

Types of Arthritis

There are two common forms of arthritis.

  • Osteoarthritis occurs when the cartilage in the knee that acts as a cushion for the bones thins and wears away. This, in turn, allows the bones to rub together causing pain and stiffness. Osteoarthritis usually occurs in patients over 50 years old, who often have a family history of arthritis.
  • Rheumatoid arthritis is a systemic disease in which there is thickening and inflammation of the synovial membrane, the tissue that produces a lubricant to help the knee move smoothly. Over time this chronic inflammation can cause cartilage damage, leading to pain and stiffness.


A number of factors interact to cause knee deterioration, including:

  • Heredity
  • Developmental abnormalities of knee formation
  • Major or minor repetitive injures
  • Certain occupations
  • Serious knee injury

While being overweight does not necessarily cause arthritis, it can contribute to early and more rapid progression of knee problems.


Different types of arthritis have different symptoms which can range in severity from person to person. Osteoarthritis generally does not cause any symptoms outside the joint. Symptoms of rheumatoid arthritis might include fatigue, fever, a rash, and the signs of joint inflammation, which include:

  • Pain
  • Swelling
  • Stiffness
  • Tenderness
  • Redness
  • Warmth

Risk Factors

Risk factors for arthritis include:

  • Age - The risk of developing arthritis, especially osteoarthritis, increases with age.
  • Gender - In general, arthritis occurs more frequently in women than in men.
  • Weight - Being overweight puts extra stress on weight-bearing joints, increasing wear and tear and the risk of arthritis.
  • Work factors - Some jobs that require repetitive movements or heavy lifting can cause stress in the joints and/or cause an injury, which can lead to arthritis.