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X-ray surveys of arthritis of the sacroiliac joints

A survey examined the frequency of x-ray changes of the sacroiliac joints. The results were divided into people with current back pain and people without current back pain. Those without back pain are referred to as ‘clinical ankylosing spondylitis’.

The back pain in ankylosing spondylitis is associated with marked stiffness, and surveys focus on this subgroup of back pain. Such surveys are rare as this joint is no longer routinely x-rayed because it would involve unnecessary radiation to the pelvic organs, so data is from studies that are over 20 years old. Also, although this joint is very frequently involved in ankylosing spondylitis, many patients won't notice any effect in this joint.

In an attempt to find the frequency of the disease (including undiagnosed cases), an ambitious 1985 Norwegian survey studied over 20,000 adults aged 20–54 years for back pain. A random sample were followed-up with x-ray and clinical examination. Based on a number of assumptions, a range of the likely number of existing cases of ankylosing spondylitis was defined. The number of cases in the UK has been estimated from these.

How common is x-ray evidence of ankylosing spondylitis?

Gender Prevalence UK estimate 
Males 8–22/1,000 116,000–318,000
Females 2–6/1,000 29,000–87,000



1.    Gran JT, Husby G, Hordvik M. Prevalence of ankylosing spondylitis in males and females in a young middle-aged population of Tromso, northern Norway. Ann Rheum Dis 1985; 44(6):359–67.

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