Inflammatory diseases, injury, infection and surrounding bone loss may all affect the health of the knee joint. Diseases affecting the knee are typically chronic and progressive, with cartilage damage, pain, swelling and mobility worsening over time. With early treatment, many knee joint diseases can be treated to reduce inflammation and pain and slow the process of joint erosion.
Arthritis
According to the American Academy of Orthopaedic Surgeons (AAOS), there are three types of arthritis that can affect the knee joint--osteoarthritis, rheumatoid arthritis and post-traumatic arthritis. Osteoarthritis is the most common form of arthritis. It is a condition that progresses slowly, characterized by a wearing away of knee joint cartilage. Rheumatoid arthritis is a chronic inflammatory disease that attacks the joints of the body. It is less common than osteoarthritis and typically occurs in people over the age of 40, according to the Dartmouth-Hitchcock Medical Center (DHMC). It generally affects both knees and, like osteoarthritis, it affects the knees by damaging joint cartilage. Post-traumatic arthritis develops after injury to the knee(s) such as a fracture, ligament damage or a meniscus tear. It is similar to osteoarthritis and often does not cause symptoms until years after an injury has occurred.
Although acute onset is possible, arthritic joint diseases generally develop slowly, causing progressive symptoms that include stiff and swollen joints, problems straightening or bending the knee, pain that worsens after periods of inactivity (sleep) or exercise (walking, climbing stairs) and a feeling of weakness in the knee(s) that causes a sensation of locking or buckling. Some people may experience worsening pain in response to changes in weather.
Infectious Arthritis
According to the DHMC, infectious arthritis (also known as bacterial/myobacterial, fungal, septic, pyogenic, or non-gonococcal/gonococcal infectious arthritis) is a condition caused by a virus, bacteria or fungus. It is characterized by joint inflammation and destruction of cartilage and often occurs after you have had an infection in another part of the body. After the germ enters the body, it travels through the bloodstream and settles in a joint. These types of infections typically infect just one joint at a time, and large joints such as the knee are among the most commonly affected. If infectious arthritis is not treated early with medication, extensive cartilage damage can occur, and the infection may spread to other parts of the body.
Osteonecrosis of the Knee
Osteonecrosis of the knee is a condition in which the inner, knobby portion of the thighbone, the outside of the knee or the top portion of the lower leg bone lose their blood supply and begin to die. Osteonecrosis is a progressive condition that develops in four stages, according to the AAOS. During stage 1, symptoms are most intense and may include sudden pain on the inside of the knee, increased pain at night or during or after activity, limited motion (due to pain), swelling and heightened sensitivity to touch in the knee area. It may take several months for the condition to progress to stage 2, which is characterized by a flattening out of the thigh or leg bone. By stage 3 (three to six months after onset), cartilage loosens and the bone begins to die. Stage 4 is characterized by progression to severe osteoarthritis. The bone begins to collapse, the cartilage around the end of the bone is destroyed, the joint space tightens and bone spurs (bony projections) may form.
