THE SACRO-ILIAC JOINT
The sacro-iliac joint is the articulation between the Spinal Column and
the Pelvis. The Sacrum, at the bottom end of the vertebral column, is
formed by 5 fused vertebrae and completes the ring formed by the two semi-circular
wing bones (iliac bones) of the pelvis. The sacrum’s trapezoideal
shape fits into an opposing space at the back of the pelvis like a keystone
to form a stable platform for the trunk, head and upper limbs to rest
The opposing surfaces of sacrum to the iliac bones on both sides are
not congruent. This, together with extremely strong ligaments between
the opposing surfaces as well as an interwoven complex of external ligaments
forms an articulation highly resistant to shear and slip.
Its only movement is a rocking motion within an arc of about 4 to 7 degrees.
Pain originating in the SI joint is not uncommon and should be considered
in the differential diagnosis of every case of low backache.
It is typically moderate to severe, unremitting and resistant to ordinary
painkillers. It is often predominantly on the left or the right side.
Pain may be aggravated by movement or by lying on the affected side. It
is relieved by rest, heat, physical therapy, and joint injections. Needle
placement for SI joint injections are difficult if not impossible to perform
without the assistance of X-ray fluoroscopy.
The incongruity of the joint makes accurate x-ray evaluation difficult,
but examination by CT scanning, MRI and nuclear bone scans have proved
helpful in distinguishing SI pain from other causes of low back pain.
The most frequently found causes of SI joint pain seems to be degenerative
arthritis with joint sepsis, tumors and trauma less common findings.
Surgery of the SI joints is rarely indicated: Mostly as fusion for joints
severely disrupted by trauma or in extreme cases of degeneration with
Results of surgery are difficult to guarantee and often less than satisfactory
and so should only be advised after careful consideration of every particular
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