Diagnosis and symptoms6 min read
Sacroiliac joint pain: the point beside the tailbone
The sacroiliac joint is a strong, minimally mobile joint connecting the sacrum to the pelvis. Pain from it is often confused with a herniated disc, though the two are separated by a few clear findings.
Typical location and pattern
Pain is felt in the dimple just beside the tailbone. Patients can usually indicate it with a single finger; this 'finger sign' is quite directive for the diagnosis.
It refers into the buttock and back of the thigh but usually does not go below the knee. Referral into the groin is also typical for this joint.
Pain is usually one-sided. Bilateral, symmetric pain calls for assessment of inflammatory joint disease.
What increases it
Standing on one leg, climbing stairs and rolling out of bed are the most typical triggers. What they share is creating shear between the two halves of the pelvis.
Prolonged sitting and standing with weight on one leg also increase it. Using a clutch while driving accentuates the one-sided load.
Pain that sharpens in the first steps of walking then eases after a few minutes is a course frequently reported for this joint.
Distinguishing it from a herniation
Sacroiliac pain does not travel below the knee or cause numbness in the foot. Coughing and straining do not markedly increase it, a finding seen in disc-related pictures.
Several tests that stress the joint are applied on examination. Three or more reproducing the familiar pain strongly supports a sacroiliac source.
Imaging is generally not directive here. Diagnosis rests on clinical tests, with MRI used more to exclude other diagnoses.
Key points
- Pain is point-like in the dimple beside the tailbone.
- Being able to indicate it with one finger is directive.
- It refers into the buttock and back of the thigh, not below the knee.
- Standing on one leg and rolling out of bed are typical triggers.
- Bilateral symmetric pain is assessed for inflammatory disease.
Frequently asked questions
Can the joint slip out of place?
No. The sacroiliac joint is bound by very strong ligaments and normally moves millimetres. The description of 'slipping out' is common but anatomically incorrect.
Why is it common in pregnancy?
Hormones released in pregnancy loosen ligaments and movement at the joint increases somewhat. Added weight and a shifted centre of gravity accentuate the picture.
Does it cause lasting damage?
It does not. Mechanical sacroiliac pain has a good course and resolves with an appropriate programme. Persistence comes from the asymmetric load producing it continuing.
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This content is for information only and does not replace medical diagnosis or treatment. Response to treatment varies between individuals. Please consult a healthcare professional about your symptoms.