How does Ankylosing Spondylitis progress?

Whenever one speaks about Ankylosing spondylitis, I’m sure picture of a man with a hunchback & restricted mobility comes to your mind. This famous photograph from the ACR library clearly describes what a patient with Ankylosing spondylitis goes through in his life. Ever wondered what really happens behind the curtain?

Ankylosing spondylitis is a chronic inflammatory arthritis affecting the sacroiliac joints (joints beneath the buttocks), vertebral joints & the hips. The joints get inflamed & persistent inflammation in the long run leads to formation of new bone.

The inflammation is responsible for the pain & the bone formation leads to restriction in movements of the spine.

Let us have a look at a simple example to understand this. The spine is similar to multiple matchboxes hung by a set of flexible threads. The flexibility of the threads is responsible for the movements of the spine. However, if you put wax on the threads & let it set, the threads do not bend. This is exactly what happens with Ankylosing Spondylitis. The threads are akin to the ligaments of the vertebrae & the matchboxes to individual vertebrae. Once the threads become hardened by inflammation (wax) the mobility is lost.

The hardened ligaments give the typical tram track or bamboo spine appearance on the X-Ray.