Ankylosing spondylitis

Ankylosing spondylitis

Ankylosing spondylitis


  • Spondyloarthropathy affecting 5/1000 of the Caucasian population – only 10% develop significant symptoms.
  • Predominantly a genetic aetiology (>90%) with HLA B27 conferring a relative risk increase of 120, although this is not the only genetic inheritance factor in ankylosing spondylitis.
  • Young adults, M: F = 3 : 1.

Clinical features

  • Thoracolumbar and lower back pain with stiffness. Buttock pain with radiation down the posterior thigh but not below the knee.
  • Morning stiffness and night pain are common.
  • Costochondral/costovertebral pain, sometimes causing respiratory disease.
  • Coexistent plantar fasciitis, iritis (30%), Achilles tendonopathy, inflammatory bowel disease (10%), psoriasis (10%) and major-joint involvement (20%). Cardiac problems occur in 1%.
  • Progressive lumbar flattening and thoracic kyphosis, in conjunction with soft-tissue flexion contractures of the hip produce the characteristic ‘question mark’ posture.
  • Further exacerbation of the thoracic kyphosis may be due to osteoporotic wedge fractures, which are not uncommon.

Radiological features

  • Sacroiliitis is a pre-requisite for diagnosis. Look for early marginal sclerosis on the iliac side of the sacroiliac joint (SIJ), usually starting in the inferior 1/3 (synovial part) of the SIJ. Complete SIJ ankylosis is a late sign.
  • Osteitis results in squaring of vertebral bodies. The earliest signs of spondylitis are manifest as small erosions at the corners of the vertebral bodies – the so-called Romanus lesion. Syndesmophyte formation eventually lead to classical ‘bamboo spine’.
  • Osteoporosis and kyphosis occur with long-standing disease.
  • Extra-axial skeletal involvement mimics mild rheumatoid arthritis.
Ankylosing spondylitis: ‘squaring-off’ of the vertebral bodies with anterior syndesmophyte formation.

Ankylosing spondylitis: ‘squaring-off’ of the vertebral bodies with anterior syndesmophyte formation.

Ankylosing spondylitis: sacro-ileitis and a ‘bamboo spine’.

Ankylosing spondylitis: sacro-ileitis and a ‘bamboo spine’.


  • NSAIDs and physiotherapy form the bulk of treatment.


James R. D. M., Erskine J. H., Rakesh R. M. (2008). Musculoskeletal Radiology. A-Z Musculoskeletal and Trauma Radiology, 1st edition, Cambridge University Press, Cambridge, 1, 1-176.


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