It is not always certain why arthritis of the knee develops. The knee may become affected by almost any form of arthritis, including those related to mechanical damage of the structures of the knee (osteoarthritis, and post-traumatic arthritis), various autoimmune forms of arthritis (including; rheumatoid arthritis, juvenile arthritis, and SLE-related arthritis, psoriatic arthritis, and ankylosing spondylitis), arthritis due to infectious causes (including Lyme disease-related arthritis), gouty arthritis, or reactive arthritis. Osteoarthritis of the knee The knee is one of the joints most commonly affected by osteoarthritis. Cartilage in the knee may begin to break down after sustained stress, leaving the bones of the knee rubbing against each other and resulting in osteoarthritis. Nearly a third of US citizens are affected by osteoarthritis of the knee by age 70. Obesity is a known and very significant risk factor for the development of osteoarthritis. Risk increases proportionally to body weight. Obesity contributes to OA development, not only by increasing the mechanical stress exerted upon the knees when standing, but also leads to increased production of compounds that may cause joint inflammation. Parity is associated with an increased risk of knee OA and likelihood of knee replacement. The risk increases in proportion to the number of children the woman has birthed. This may be due to weight gain after pregnancy, or increased body weight and consequent joint stress during pregnancy. Flat feet are a significant risk factor for the development of osteoarthritis. Additionally, structural deformities, advanced age, female sex, past joint trauma, genetic predisposition, and certain at-risk occupations may all contribute to the development of osteoarthritis in general. Lyme disease-related arthritis of the knee The knee is often the first joint affected in Lyme disease. Systemic lupus erythematosus Arthritis is a common symptom of SLE. Arthritis is often symmetric and more often involves small joints. Though almost any joint may be affected, the knees and joints of the hands are most often involved in SLE. In larger joints (including the knee), avascular necrosis is a possible complication, leading to further pain and disability. Reactive arthritis Reactive arthritis often presents with lower limb oligoarthritis, including that of the knee. Gout Arthritis of a single joint of the lower extremities with rapid onset is highly suggestive of gouty arthritis. The knee may sometimes be affected. In cases of gouty arthritis of the knee, skin symptoms occur less often, however pain and swelling may be particularly intense. Rheumatoid arthritis RA most often first manifests as inflammation of particular finger or toe joints, however, pain and swelling of larger joints, including the knees, may also be the first sign.
Knee arthritis
Knee effusion
Shoulder arthritis
Sacroiliitis
Osteochondritis
Knee dislocation
Septic arthritis
Ankle flare