The synovial membrane thickens, and the fluid-filled space inside the joint becomes smaller. There is often inflammation. As osteoarthritis gets worse, bits of cartilage may break away from the bone, causing the bone ends to rub together and the ligaments to become strained. This causes a lot of pain, and changes the shape of the joint. Osteoarthritis is most common in hands, knees, hips and feet.
Some people also develop it in the back and neck.
Osteoarthritis develops very differently from person to person. The condition typically causes joints to become stiff and painful to move, but it does not usually cause symptoms outside the area of the joint. It usually develops slowly, and the changes can be so gradual that people hardly notice them. The condition usually settles down after a number of years, and although the joints may have a knobbly appearance they can become more free of pain. The BBC is not liable for the contents of any external internet sites listed, nor does it endorse any commercial product or service mentioned or advised on any of the sites.