Ankylosing Spondylitis



  • Chronic inflammatory disease, primarily affects the axial skeleton with predilection toward the spine and sacroiliac (SI) joints:
    • SI joints 100%
    • Cervical spine 75%
    • Thoracic spine 70%
    • LS spine 50%
    • Hip joints 30%
    • Shoulder joints 30%
  • Spondylitis (inflammation of vertebrae) of ankylosing spondylitis (AS) begins at the insertions of the outer fibers of the annulus fibrosus (enthesitis) of the vertebrae:
    • Ossification (syndesmophyte formation) may lead to complete fusion, ankylosis, of the vertebrae
    • Extensive spinal involvement causes the radiographic appearance of the brittle “bamboo spine”
  • Onset 15–35 yr of age. Rarely after age 45
  • Male to female ratio is between 2:1–3:1

AS patients are at 4 times the risk for fracture and paralysis compared to the general population. They are 11 times more likely to have spinal cord injuries

Risk Factors

Strong genetic component. HLA-B27 is present in 80–90% of patients with AS


Disease is likely triggered by environmental factors such as infection in genetically predisposed individuals

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