Osteoarthritis (OA), also called degenerative arthritis, is the most common type of arthritis. People tend to develop OA as they age. In OA, the smooth cartilage that cushions your joint breaks down, bone spurs at the side of joints form, and the bone underneath the cartilage hardens. These changes cause pain, swelling and problems moving the joint. Because of pain and decreased physical activity, the muscles that support the joints can weaken. Your family history, being overweight, past joint injury and joint overuse can make you more likely to develop OA.
How much joint pain you feel does not always match the amount of damage to your joint. Some people with little damage have a great deal of pain, and some people with a lot of damage have little pain. Osteoarthritis pain is often at its worst when bone rubs against bone after cartilage is gone, but it can also be caused by the following:
- Bone microfractures. When cartilage is lost, more stress is placed on the bone underneath the cartilage. This may result in bone bruises or tiny fractures (breaks or cracks in the bone), which cause pain. The healing of the microfractures hardens the bone, which increases stresses on the joint.
- Osteophytes. Bone spurs are small bony growths on top of existing bone. They can occur at the sides of joints and cause pain.
- Synovitis. The inside of your joint is lined with a membrane called the synovium. The synovium produces a liquid (synovial fluid) that helps the joint move smoothly and keeps it healthy. Sometimes the lining gets inflamed (synovitis), and too much fluid builds up in the joint. This can occur in osteoarthritis, but it does not happen as often or as much as in inflammatory arthritis, like rheumatoid arthritis.
- Muscle weakness. Joint pain and inactivity can lead to muscle weakness. This weakness can increase stress on the joint, which leads to more pain, inactivity and weakness.
- Ligament damage. Ligaments are bands of flexible tissue that connect the bones of the body together. The disease process of OA can cause painful ligament damage. Ligament injury (that sometimes happens while playing sports) can also cause OA.
- Centralized pain. The chronic (long-lasting) pain of OA can in some cases cause people to become more sensitive to pain.