Rheumatoid arthritis (RA) is the most debilitating type of arthritis because it can cause adult deformity and disability. It affects more than 1.5 million adult Americans. The type of RA that affects children is Juvenile Idiopathic Arthritis (JIA). RA's onset usually occurs between the ages of 30 and 60, but is known to affect older adults, too. Women are affected three times as often as men.
In the spine, RA usually affects the joints in the neck (cervical spine). It is an autoimmune disease: the body’s own immune system attacks joints and connective tissue, leading to pain, swelling, and stiffness. Some patients experience disability and loss of joint function. There are many other types of arthritis, including osteoarthritis (spondylosis), a type that commonly affects the spine.
Rheumatoid Arthritis in the Spine
The bones of the spine are the vertebrae (eg, vertebral bodies). The spine is divided into 4 regions: cervical (neck), thoracic (upper or mid-back), lumbar (lower back), and sacral (sacrum, back of the pelvis).
A vertebra has 2 pairs of facet (zygoaphophyseal or apophyseal) joints; located on each side at the back of the vertebral body: one pair faces upward, the other pair downward. These hinge-like joints link the vertebrae together and play an important role in flexibility and mobility.
To learn the basics about the anatomy of the spine, click here to watch an educational animation.
The joint surfaces are covered with cartilage to allow the joints to move smoothly against each other. As with other joints, the facet joints are surrounded by a thin layer of connective tissue called the synovium, which produces synovial fluid for lubrication and nourishment. When rheumatoid arthritis develops, the immune system mistakenly identifies the synovium as “foreign” and attacks it, leading to inflammation. A cascade of chemicals causes the synovium to thicken, resulting in swelling. Over time, the inflammation can destroy the cartilage and bone, and the muscles, tendons, and ligaments supporting the joint in turn weaken and lose function.
Similar, but Different
Rheumatoid arthritis is sometimes confused with a different type of inflammatory arthritis that affects the spine—ankylosing spondylitis (AS). It is similar to RA in that AS is a chronic disease that affects the spine’s joint, but can also develop in other joints in the body. Ankylosing or the Greek word ankylos means joint stiffness; and, spondylitis in Greek, spondylo means vertebra.
The symptoms of ankylosing spondylitis are similar to RA: skin redness, heat, joint swelling, and pain. In the spine, AS may involve the sacroiliac (SI) joints that join the spine to the pelvis. AS causes new bone to grow, fusing two or more vertebrae together, which may lead to abnormal curvature of the spine.
Although both RA and AS attack the spine, they are 2 separate conditions and require diagnosis by a rheumatologist.