Knee pain in adults that isn't the direct result of trauma is most likely caused by a type of arthritis. Osteoarthritis is by far the most common cause of arthritis of the knee, followed by traumatic arthritis (also called post-traumatic arthritis) and rheumatoid arthritis.
This common form of arthritis usually occurs in one or both knee joints. It is marked by the degeneration of articular cartilage that covers and protects the tibia (shin bone), femur (thigh bone), and patella (knee cap) at the knee joint. Cartilage does not have blood flow or nerve endings, so it is possible to have damaged articular cartilage and experience no pain. However, a person can experience pain when degenerated cartilage causes bone to rub against bone or compromises the joint function some other way. It is usually characterized as follows:
- In the early stages of knee osteoarthritis, pain may be felt when doing specific activities that cause impact between the bones, such as jumping or participating in sports.
- As osteoarthritis progresses, going up or down stairs and other daily activities can be become painful. Knee locking or buckling may occur. Other parts of the knee joint may be affected. For example, osteophytes (bone spurs) may grow, thereby increasing friction, stiffness, and pain; the femur and tibia may fall out of alignment; and/or ligaments may become stressed. A persistent dull ache in the knee may develop and stiffness (sometimes accompanied by swelling of the knee) may become more frequent. NSAIDs such as Aleve and Motrin may become necessary to help manage pain.
- Severe knee osteoarthritis significantly affects a person’s mobility and can be marked by bouts of severe and unexpected knee pain.
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Post-Traumatic Knee Arthritis
This type of arthritis develops after a trauma or injury (post-traumatic or traumatic arthritis) to the knee, such as a bone fracture, meniscus tear, or ligament injury. As a result of the injury, the cartilage cells gradually degenerate. The articular cartilage may detach and decompose into fragments that disrupt normal knee movement and cause pain.
This type of arthritis may not develop or become symptomatic until years after the injury. It typically develops over a long period of time and includes symptoms similar to knee osteoarthritis.
An immune system disease that initially presents itself in people ages 20-50 years, rheumatoid arthritis can cause knee pain. Rheumatoid arthritis is caused when the white blood cells - which normally protect the body from infection, bacteria, and viruses - start destroying the synovial lining of the joint. The synovial lining encapsulates the knee joint and produces lubricating synovial fluid that aids knee function. When the synovial lining is injured it swells, causing warmth and redness, tenderness, and pain in the knee joint. In one clinical study, a person likened the warmth to "sitting too close to the fire."
People who suffer from rheumatoid arthritis in the knee usually experience it symmetrically (if one knee is affected so is the other) and also have symptoms in their hands and wrists. Episodes of rheumatoid arthritis may come and go and can be accompanied by fever and fatigue and a general run-down feeling.
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While the above three types of arthritis represent the most common cause of arthritic knee pain, any one of the more than 100 types of arthritis may include knee symptoms. However, other types of arthritis usually do not present with knee pain as the most prominent symptom.
- Hawker GA, Stewart L, et al., "Understanding the pain experience in hip and knee osteoarthritis--an OARSI/OMERACT initiative," Osteoarthritis Cartilage, Vol. 16 Issue 4 (April 2008):415-22.