Spinal Issues and Ankylosing Spondylitis

Reviewed by: HU Medical Review Board | Last reviewed: February 2019 | Last updated: March 2021

Because ankylosing spondylitis (AS) most often affects the spine, it can cause complications to the spine including spinal fracture, kyphosis, and stenosis. AS causes chronic inflammation in the vertebral joints and in the points where tendons and ligaments attach to the joints, called entheses. This chronic inflammation wears away at the bone of the joints. As the body works to replace the lost bone, it can create excess bone, leading to a fusing of the joint.

The entheses and ligaments may also become calcified and hard, called syndesmophytes. As the condition develops and the spine becomes more immobilized by the formation of bone in the joints, the spine can take on the appearance of bamboo on x-rays and is referred to as "bamboo spine." The presence of bamboo spine increases a person's risk of fractures in the vertebrae.1-3

Spinal fractures and ankylosing spondylitis

Spinal fractures are cracks or breaks in the vertebrae. Spinal fractures may occur in the lumbar (low back), thoracic (mid back) or cervical (neck) spine. Spinal fractures can range from mild to severe.4,5 Cervical fractures in people with AS are the most dangerous, as they increase the risk of neurologic impairment and can be fatal.5

When AS progresses and causes fused joints in the spine, the spine isn't able to bend and flex and becomes rigid and less stable. The fused joints are weak and brittle and put a person at increased risk of spinal fractures. Spinal fractures may occur when there is trauma, such as a fall or car accident, or they may occur in weakened bones with minor activity, such as reaching or twisting.1,4 In addition to AS, osteoporosis can weaken bones and increase the risk of spinal fractures. People with AS are at an increased risk of osteoporosis.6 Research has found that people with AS are up to four times more likely to experience spinal fractures than others in the general population.5

Spinal fractures that are mild may go unnoticed for some time, while more severe spinal fractures can cause severe pain and may damage the spinal cord. Fractures in the thoracic or lumbar spine can cause pain that is worse with movement.4 (This is different than the usual pain from AS, which is improved with activity.) Treatment for spinal fractures may involve a brace or surgery.5

Kyphosis ankylosing spondylitis

Kyphosis is an outward curvature of the spine, which can cause a hunched or rounded back. This can cause a forward-stooped posture and in certain cases, can impact a person's ability to fully inflate their lungs. Kyphosis can vary in severity from mild to severe, with milder curvatures causing less pain.1,7

With advances in treatment of AS, kyphosis is now less common, although it can occur in severe cases of AS. Severe kyphosis may require surgery to reduce the pain and deformity and increase a person's quality of life.1,8

Spinal stenosis and ankylosing spondylitis

Spinal stenosis is a narrowing of the spinal column. Spinal stenosis may affect the space where the spinal cord is (in the middle of the spinal column), the space where the nerves come out from the spinal cord to the rest of the body, or the space between the vertebrae.9,10

Spinal stenosis can cause pain in the back or arms and legs. It may also cause a numbness or weakness of the arms or legs. A severe type of spinal stenosis is called cauda equina syndrome, which can lead to a loss of control of the bowels or bladder. Treatment for spinal stenosis may involve medications to reduce the pain or surgery to correct nerve damage.9

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