Ankylosing Spondylitis

Ankylosing spondylitis (AS) is an inflammatory condition mainly affecting the spine that causes progressive stiffness and pain. It is part of the seronegative spondyloarthropathy group of conditions relating to the HLA B27 gene. Other conditions in this group are reactive arthritis and psoriatic arthritis.

The key joints that are affected in AS are the sacroiliac joints and the joints of the vertebral column. The inflammation causes pain and stiffness in these joints. It can progress to fusion of the spine and sacroiliac joints. Fusion of the spine leads to the classical “bamboo spine” finding on spinal xray that often appears in medical exams.

There is a strong link with the HLA B27 gene. Around 90% of patients with AS have the HLA B27 gene however around 2% of people with the gene will get AS. This number is higher (around 20%) if they have a first degree relative that is affected.



The typical exam presentation is a young adult male in their late teens or 20s. NICE guidelines (2017) give guidance on the diagnosis of spondyloarthritis. They highlight that it affects women and men in similar numbers. Symptoms develop gradually over more than 3 months.

The main presenting features are lower back pain and stiffness and sacroiliac pain in the buttock region. The pain and stiffness is worse with rest and improves with movement. The pain is worse at night and in the morning and may wake them from sleep. It takes at least 30 minutes for the stiffness to improve in the morning and it gets progressively better with activity throughout the day.

Symptoms can fluctuate with “flares” of worsening symptoms and other periods where symptoms improve.

Vertebral fractures are a key complication of AS.


Ankylosing spondylitis does not only affect the spine. It can affect other organ systems causing:

  • Systemic symptoms such as weight loss and fatigue
  • Chest pain related to costovertebral and costosternal joints
  • Enthesitis is inflammation of the entheses. This is where tendons or ligaments insert in to bone. This can cause problems such as plantar fasciitis and achilles tendonitis.
  • Dactylitis is inflammation in a finger or toe.
  • Anaemia
  • Anterior uveitis
  • Aortitis is inflammation of the aorta
  • Heart block can be caused by fibrosis of the heart’s conductive system
  • Restrictive lung disease can be caused by restricted chest wall movement
  • Pulmonary fibrosis at the upper lobes of the lungs occurs in around 1% of AS patients
  • Inflammatory bowel disease is a condition associated with AS

Schober’s Test

This is a test used as part of a general examination of the spine to assess how much mobility there is in the spine. You might be asked to do it in your OSCE examinations.

Have the patient stand straight. Find the L5 vertebrae. Mark a point 10cm above and 5cm below this point (15cm apart from each other). Then ask the patient to bend forward as far as they can and measure the distance between the points.

If the distance with them bending forwards is less than 20cm, this indicates a restriction in lumbar movement and will help support a diagnosis of ankylosing spondylitis.


  • Inflammatory markers (CRP and ESR) may rise with disease activity
  • HLA B27 genetic test
  • Xray of the spine and sacrum
  • MRI of the spine can show bone marrow oedema early in the disease before there are any xray changes


Xray Changes

Bamboo spine” is the typical exam description of the xray appearance of the spine in later stage ankylosing spondylitis. This is worth remembering for your exams.

Xray images in ankylosing spondylitis can show:

  • Squaring of the vertebral bodies
  • Subchondral sclerosis and erosions
  • Syndesmophytes are areas of bone growth where the ligaments insert into the bone. They occur related to the ligaments supporting the intervertebral joints.
  • Ossification of the ligaments, discs and joints. This is where these structures turn to bone.
  • Fusion of the facet, sacroiliac and costovertebral joints




  • NSAIDs can be used to help with for pain. If the improvement is not adequate after 2-4 weeks of a maximum dose then consider switching to another NSAID.
  • Steroids can be use during flares to control symptoms. This could oral, intramuscular slow release injections or joint injections.
  • Anti-TNF medications such as etanercept or a monoclonal antibody against TNF such as infliximab, adalimumab or certolizumab pegol are known to be effective in treating the disease activity in AS.
  • Secukinumab is a monoclonal antibody against interleukin-17. It is recommended by NICE if the response to NSAIDS and TNF inhibitors is inadequate.

Additional management:

  • Physiotherapy
  • Exercise and mobilisation
  • Avoid smoking
  • Bisphosphonates to treat osteoporosis
  • Treatment of complications
  • Surgery is occasionally required for deformities to the spine or other joints


Last updated March 2019
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