What it is
The sacroiliac joints connect the base of the spine to the pelvis. They move very little, but they carry load, and they can become a genuine source of pain — after pregnancy, after trauma, with inflammatory arthritis, or following a lumbar fusion that transfers load onto them.
It is one of the more commonly missed diagnoses in the lower back, because the pain pattern overlaps with disc and facet pain.
Symptoms
- Pain low down and to one side, often pointed to just below the belt line
- Pain into the buttock and back of the thigh, usually not below the knee
- Worse with standing from sitting, rolling in bed, or climbing stairs
- Often described as being "in the hip" when it is not the hip joint at all
How it is diagnosed
A cluster of provocation tests on examination raises the suspicion. The diagnosis is confirmed by an image-guided injection of local anesthetic into the joint: if the pain goes away while the anesthetic is working, the joint is the source. Imaging is used mainly to exclude other causes.
Non-surgical treatment
Physical therapy aimed at the pelvis and hip stabilizers, a belt in some cases, anti-inflammatory medication, and therapeutic injections. Radiofrequency ablation of the nerves supplying the joint can give longer relief.
When surgery is considered
Only after the diagnosis has been confirmed by injection and non-operative treatment has genuinely failed over a sustained period. Fusing the joint is a reasonable option in that narrow group and an unreliable one outside it, which is why the diagnostic work comes first.