The Progression of Ankylosing Spondylitis

The healthy vertebral column, or spine, is flexible, yet it is perfectly suited to its primary job, which is to protect the vulnerable nerves of the spinal cord. Like interlocking puzzle pieces, the bones of the vertebral column fit together perfectly, allowing flexibility of the body without compromising spinal cord protection. Between individual vertebrae, we see discs of tough cartilage, shown in blue. As the slider moves forward, the bones of the vertebrae become transparent, allowing us to glimpse the internal anatomy of these intervertebral (spinal) discs shown in red.

Here we see a view of the spinal column at the level of the chest, showing some of the ribs, attached at the thoracic region of the spinal column. Intervertebral discs are shown in blue. As normal aging progresses, the tissue of the cushioning intervertebral discs develops small tears and cracks. At the same time, the inner gel-like nucleus pulposus gradually loses water, and with it, the ability to absorb shocks efficiently. Eventually the outer rings of the annulus fibrosus weaken and tear, reducing flexibility and possibly causing pain.

Ankylosing spondylitis (AS) is a degenerative autoimmune disease; a form of inflammatory arthritis that mostly affects the spine. Although no one knows what causes the inflammation that ultimately results in the development of “stiff vertebrae,” people with AS are believed to have a strong genetic predisposition for the disease. Here we see the progressive inflammation as it affects the bones of the vertebrae ("T12", "L1", and "L2" refer to bones in the lumbar region of the spine), causing excess growth resulting in projections called “bony protuberances,” and considerable pain.

Here we see the progression of the disease. As vertebrae continue to grow they eventually fuse together, encasing the shock-absorbing spinal discs, and severely limiting the flexibility of the spine. Once the vertebrae become fused, the patient is said to have “bamboo spine.”

There is presently no cure for AS, although drugs are often used to reduce inflammation and pain, and to slow the disease’s progression. Physical therapy and/or exercise may be prescribed, and some physicians believe that maintaining good posture may help prevent a fused or curved spine.

By moving the slider back and forth, it’s easy to visualize the contrast between a normal spine and a spine affected by ankylosing spondylitis. On the left, we see the relative inflexibility of the AS spine, compared with the flexibility of a normal spine. In this comparison, the vertebrae of the lower spine have fused together in the left-hand image, making it difficult for the affected individual to bend backwards and forwards, as needed. People with AS often must rely on a cane to walk, and may find it difficult to sit or stand for extended periods of time.

Although there is no cure for AS presently, therapies are available to reduce inflammation and pain, and to slow the progression of the disease. Treatments ranfe from over-the-counter anti-inflammatory drugs like ibuprofen and aspirin to corticosteroid injections to more complex treatments like cyclosporin and adamilumab.

Learn more about AS Treatment Options.