The SIJ (Sacroiliac Joint)
Updated: Oct 15
By Andy Duckmanton, BOst (Hons), GOsC registered osteopath.
Editorial update: 15 October 2026.
The sacroiliac joints (SIJs) connect the sacrum at the base of the spine to the pelvic bones. Pain around this region may be felt in the lower back or buttock, but the location alone does not show that the SIJ is the source.
The Role of the SIJ
These joints have relatively little movement and help transfer load between the trunk and legs. Pain around them can have several possible causes. Assessment also considers the lower back, hips and relevant medical conditions rather than assuming the pelvis is out of alignment.
The SIJ in Pregnancy
Pelvic girdle pain during pregnancy can affect the back or front of the pelvis and sometimes the hips or thighs. It should not automatically be attributed to one hormone or a loose joint. Tell your midwife or GP about symptoms so that appropriate assessment and support can be arranged.
Referred Pain
Pain from structures around the lower back and pelvis can sometimes be felt elsewhere, including the buttock or thigh. This can overlap with sciatica, which involves nerve irritation or compression. A dull ache, shooting pain or tenderness alone cannot confirm which structure is involved. Numbness or weakness needs particular attention during assessment.
Managing SIJ Pain
Andy will ask about your symptoms and medical history and assess relevant movement and physical findings. The aim is to consider possible causes and whether osteopathic care or further medical assessment is appropriate. Persistent pelvic pain during or after pregnancy should also be discussed with your maternity team or GP.
Where appropriate, a management plan may include advice about activity, exercises and hands-on treatment. It should be adapted to your symptoms and goals, with progress reviewed. There is no single treatment that reliably resolves all pain around the SIJ. Our low back pain guide explains more about assessment and when to seek medical help.
Go to A&E or call 999 if back or leg symptoms include sciatica on both sides, severe or worsening weakness or numbness in both legs, numbness around the genitals or bottom, or new difficulty controlling or passing urine or controlling bowel movements. These can be signs of a serious spinal problem. See the NHS sciatica guidance for details. Do not wait for a routine appointment.