SI Joint



Sacroiliac joint is a pair of special joints located between the lower back and the hip joint.  Although they move a few degrees during normal locomotion they are critical in weight transfer and are two weight bearing joints.  These joints get loaded particularly at the time of sitting and negotiating gradient.  The importance of a sacroiliac joint as the cause of low back pain has been highlighted in recent medical literature.  Studies have shown that up to 25% (a quarter) of low back pain could be attributed to the sacroiliac joint.


Sacroiliac joints, being a synovial joint, can get affected by any arthritic condition which affects the other joints like the hips and knees.  These conditions include osteoarthritis, rheumatoid arthritis, gout, ankylosing spondylitis etc.  Sacroiliac joint can also get affected by post-pregnancy instability and subtle injury to pelvis during difficult childbirth.  Sacroiliac joint dysfunction is also quite common secondary to blunt injury to the pelvis and low back particularly due to mechanical fall.  These joints can also become painful following secondary involvement and arthritis following high velocity pelvic ring injuries.

More recently, sacroiliac joint problems have been identified to be caused by previous hip operation, particularly fusion of the lower lumbar spine due to secondary stress transfer.  


Patient's with sacroiliac joint disorder present with either uni-lateral (one-sided) or bi-lateral (both sided) low back and buttock pain.  Typically the pain radiates to the thighs up to the knee and can also radiate to the groin, hip and lower abdomen.  It is unusual for sacroiliac joint pain to radiate below the knee and it is usually not associated with tingling and numbness in the feet.  Typically patients with sacroiliac joint dysfunction would struggle to sit square on a firm surface and would fidget around as they are not able to load the affected sacroiliac joint.  They would also find it difficult to turn in bed and negotiate gradient and climb stairs.  In advance cases patients with sacroiliac joint disorder would find it very difficult to walk unassisted and they would have to rely on crutches or a wheelchair.


It is difficult to isolate sacroiliac joint pain from pain arising from the lower lumbar spine particularly due to the close proximity of the two structures.  After a careful history, clinical examination and provocative tests, various investigations like plain x-ray and MRI scan are carried out. These investigations although not diagnostic of sacroiliac joint conditions, help to rule out all other pathology around that area.  The accurate diagnosis of sacroiliac joint dysfunction relies on an image guided injection of local anaesthetic to the suspected sacroiliac joint.  These injections can be done either under CT scan guidance or fluoroscopic control.  Positive response of pain relief following an image guided injection leads to the diagnosis of sacroiliac joint dysfunction.



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