The Sacro-Iliac Joint
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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 on.

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 unremitting pain.
Results of surgery are difficult to guarantee and often less than satisfactory and so should only be advised after careful consideration of every particular case

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