TCMTCM Clinic ASHolistic and Individually Tailored Treatment

“False” Low Back Pain: Sacroiliac Joint Dysfunction

Illustration of the sacrum, pelvis and sacroiliac joints, with the joint area highlighted.

Some people experience recurring “lower back pain,” but the problem may not actually come from the lumbar spine. Instead, it may originate lower down, from the sacroiliac (SI) joint. [1],[2]

The sacroiliac joints are located between the sacrum and the left and right sides of the pelvis. They form an important connection between the spine and the pelvis. During movement, forces from the upper body are transmitted through this area to the legs. [1],[2]

Problems with joint stability, muscle function, or loading may contribute to pain in the lower back, sacral area, or buttocks. The cause is not always clear. [1],[2]

Common symptoms

Possible symptoms include: [1],[2],[3]

  • Pain or stiffness when getting out of bed
  • Pain when standing up after sitting for a long time
  • Discomfort after prolonged standing
  • Pain when turning in bed, climbing stairs, or putting weight on one leg
  • Pain that may radiate into the buttock, thigh, or groin
  • In some people, symptoms may ease after moving around for a while; this is not specific to SI joint dysfunction

Long sitting test (supine-to-sit test)

This test compares the relative positions of the medial malleoli (the bony prominences on the inner sides of the ankles) as a person moves from lying on their back to sitting with both legs straight. It has traditionally been used to assess apparent or functional leg-length differences and possible rotation of the pelvic innominate bones. [5]

Traditional interpretation for the same leg, relative to the opposite side:

  • Longer when lying → shorter when sitting: traditionally interpreted as suggesting anterior innominate rotation on that side.
  • Shorter when lying → longer when sitting: traditionally interpreted as suggesting posterior innominate rotation on that side.

These are traditional interpretations, not a confirmed diagnosis. Apparent changes do not mean that the bones of the leg have changed length. Muscle tightness and positioning can affect the result.

Research does not support using this test alone to identify innominate rotation; it cannot by itself establish SI joint dysfunction or distinguish a functional discrepancy from a true difference in bone length. Findings should be interpreted alongside the history and a complete clinical examination. [5],[6]

Why assessment matters

Symptoms alone do not establish the diagnosis. A clinical assessment should also consider the lumbar spine, hips and other causes. [1],[2],[4]

Morning stiffness that improves with movement can also occur with inflammatory sacroiliitis. Sacroiliitis and mechanical SI joint dysfunction are not identical; persistent symptoms should be assessed by a qualified healthcare professional. [3]

References

  1. Newman DP, Soto AT. Sacroiliac Joint Dysfunction: Diagnosis and Treatment. American Family Physician. 2022;105(3):239–245.
  2. Mayo Clinic Orthopedics & Sports Medicine. Sacroiliac joint pain — Overview.
  3. Mayo Clinic. Sacroiliitis — Symptoms and causes.
  4. American Academy of Pain Medicine. Sacroiliac Joint Complex Pain Guideline. Multispecialty international consensus guidelines, 2025.
  5. Schamberger W. The Malalignment Syndrome, 2nd edition: Common presentations and diagnostic techniques. Elsevier, 2013. Sitting–lying test, pp. 73–81 (traditional interpretation and potential false positives).
  6. Levangie PK. Four clinical tests of sacroiliac joint dysfunction: the association of test results with innominate torsion among patients with and without low back pain. Physical Therapy. 1999;79(11):1043–1057 (limitations of diagnostic validity).

Sources checked: 3 October 2026.