Osteoarthritis. Illustration of a coronal (frontal) section through a knee joint, showing the effects of osteoarthritis. Osteoarthritis is a joint disease aggravated by mechanical stress. Symptoms include joint pain, stiffness and swelling. Visible here is erosion of cartilage (light blue), formation of bony spurs (osteophytes) at the joint margins (on both the femur and tibia), and a thickened joint capsule (orange). The synovial membrane (pink) is also shown, with the synovial cavity shown with purple stripes. Villous formations (protrusions) have formed in the synovial membrane. For the same joint with rheumatoid arthritis, see image C029/0670.