Arthritis Mechanics

Before we can understand how arthritis does its damage, we need to understand the workings of healthy joints. There are many types of joints in the human body, but in all of them the bone ends that come together to form the joint are covered with a smooth material called cartilage. In a healthy joint, the cartilage cushions the bone and allows the joint to move smoothly and easily. The joint is also enclosed by a fibrous envelope called the synovium which produces a fluid that helps to reduce friction and wear.

In osteoarthritis, the cartilage begins to get damaged and wear away just from long-term use (or overuse). exposing bone surfaces which rub together and cause more damage. This results in inflammation, in which the tissues in and around the joint swell, further interfering with the proper functioning of the joint. The stressed bone surfaces may then start forming abnormal growths, known as bone spurs, which can cause yet more irritation and swelling, leading to additional damage. Eventually, between the damage, swelling, and accompanying pain, the joint can become harder and harder to move--doctors describe this as decreased range of motion.

In rheumatoid arthritis, the joint lining swells, invading surrounding tissues, and producing chemical substances that attack and destroy the joint surface. This commonly occurs in joints in the hands and feet. Larger joints such as hips, knees, and elbows also may be involved. Swelling, pain, and stiffness are usually present even when the joint is not used. Many joints of the body may be involved at the same time.