Why can ankylosing spondylitis produce a bamboo spine appearance on X-rays?

The "bamboo spine" appearance seen on X-rays in patients with ankylosing spondylitis is the result of extensive inflammation of the vertebral column.1

This condition is a type of spondyloarthropathy characterized by ankylosis—the fusion of joints—and spinal deformity. As the disease progresses from the sacroiliac joints upward through the spine, the chronic inflammation leads to the structural fusion of the vertebrae. This rigid, fused state of the spinal column creates the characteristic radiographic appearance often described as a "bamboo spine" due to the loss of normal spinal flexibility and the uniform, column-like look of the fused bones.21