The knee is the largest joint in the body and is central to nearly every routine activity. The knee joint is formed by the ends of 3 bones:
- The lower end of the thigh bone, or femur.
- The upper end of the shin bone, or tibia.
- The kneecap, or patella.
Thick, tough tissue bands called ligaments connect the bones and stabilize the joint.
A smooth, plastic like lining called cartilage covers the ends of the bones and prevents them from rubbing against each other, allowing for flexible and nearly frictionless movement. Cartilage also serves as a shock absorber, cushioning the bones from the forces between them. Finally a soft tissue called synovium lines the joint and produces a lubricating fluid that reduces friction and wear.
Common Causes of Knee Pain
Osteoarthritis (OA) is sometimes called degenerative arthritis because it is a "wearing out" condition involving the breakdown of cartilage in the joints. When cartilage wears away, the bones rub against each other, causing pain and stiffness.
Rheumatoid Arthritis (RA) produces chemical changes in the synovium (the lining of the joints) that causes it to become thickened and inflamed. In turn, the synovial fluid destroys cartilage. The end result is cartilage loss, pain, and stiffness.
Sarcomas are a diverse and relatively rare group of malignant tumors that develop in soft tissue and bone. They are named by the tissue of origin; for example, osteosarcomas develop in bone, liposarcomas form in fat, rhabdomyosarcomas form in muscle and Ewing sarcomas form in bone and soft tissue.3