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Ankylosing spondylitis

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Ankylosing spondylitis (AS) is a type of inflammatory arthritis in which there is a long-term inflammation of the joints of the spine

Primary Area Effected by Ankylosing Spondylitis
Primary Area Effected by Ankylosing Spondylitis

Ankylosing spondylitis is a form of ongoing joint inflammation (chronic inflammatory arthritis) that primarily affects the spine.


No one knows the cause of ankylosing spondylitis. Studies show, however, that both genes and things in our environment may lead to the development of the disease.

Risk factors

  • Anyone can get ankylosing spondylitis; however, certain factors may increase your risk for developing the disease, such as:
  • Family history and genetics. If you have a family history of ankylosing spondylitis, you are more likely to develop the disease.
  • Age. Most people develop symptoms of ankylosing spondylitis before age 45.  
  • Sex. Men are more likely to have ankylosing spondylitis than women.
  • Other conditions. People who have Crohn’s disease, ulcerative colitis, or psoriasis may be more likely to develop the disease.

Signs and symptoms

Illustration depicting ankylosing spondylitis

AS is characterized by back pain and stiffness that typically appear in adolescence or early adulthood. Over time, back movement gradually becomes limited as the bones of the spine (vertebrae) fuse together. This progressive bony fusion is called ankylosis.

Progressive disease

  • As the disease progresses, loss of spinal mobility and chest expansion, with a limitation of anterior flexion, lateral flexion, and extension of the lumbar spine, are seen. Systemic features are common, with weight loss, fever, or fatigue often present.
  • Pain is often severe at rest but may improve with physical activity, but inflammation and pain to varying degrees may recur regardless of rest and movement.
Ankylosing spondylitis lumbar spine
Ankylosing spondylitis lumbar spine

Other joint and systemic involvement


The ankylosis process
  • Ankylosing spondylitis (AS) is a systemic rheumatic disease, meaning it affects the entire body.
  • Approximately 90% of people with AS express the HLA-B27 genotype, meaning there is a strong genetic association.
  • 1–2% of individuals with the HLA-B27 genotype develop the disease.

HLA-B27 association

The association of AS with HLA-B27 suggests the condition involves CD8 T cells, which interact with HLA-B.

Bamboo spine

"Bamboo spine" develops when the outer fibers of the fibrous ring (anulus fibrosus disci intervertebralis) of the intervertebral discs ossify, which results in the formation of marginal syndesmophytes between adjoining vertebrae.



34-year-old male with AS. Inflammatory lesions of the anterior chest wall are shown (curved arrows). Inflammatory changes are seen in the lower thoracic spine and L1 (arrows).

Schober's test

The Schober's test is a useful clinical measure of flexion of the lumbar spine performed during the physical examination.


There is no cure for AS, although treatments and medications can reduce symptoms and pain.


Medications used to treat the progression of the disease include the following:


In severe cases of AS, surgery can be an option in the form of joint replacements, particularly in the knees and hips. Surgical correction is also possible for those with severe flexion deformities (severe downward curvature) of the spine, particularly in the neck, although this procedure is considered very risky. In addition, AS can have some manifestations which make anesthesia more complex. Changes in the upper airway can lead to difficulties in intubating the airway, spinal and epidural anesthesia may be difficult owing to calcification of ligaments, and a small number of people have aortic insufficiency. The stiffness of the thoracic ribs results in ventilation being mainly diaphragm-driven, so there may also be a decrease in pulmonary function.

Physical therapy

Though physical therapy remedies have been scarcely documented, some therapeutic exercises are used to help manage lower back, neck, knee, and shoulder pain.

Other names

  • Bechterew disease
  • Marie-Struempell disease
  • spondylarthritis ankylopoietica
  • spondylitis ankylopoietica
  • spondylitis, ankylosing
  • spondyloarthritis ankylopoietica

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