Sacroiliac Joint Fusion
The bony ring of the pelvis is made up of the sacrum and 3 bones that make up the pelvis, the iliac, ischial and pubic bones. The ring is joined at the front by the pubic symphysis. The ring is joined at the back on either side of the sacrum by the sacroiliac joints.
Although the joint only moves by a few degrees in adults, it plays an important role in nearly all physical activities. Almost the entire transmission of force between the upper and lower half of the body takes place via the sacroiliac joints. As with most other moving joints in the human body, degenerative arthritis can develop.
Literature suggests that up to 15-20% of patients presenting with lower back/buttock pain to a spine surgeon’s clinic have symptoms arising from degenerative disease of the sacroiliac joint either alone or in combination with symptomatic lumbar degenerative disease.
Treatment of this condition has been difficult and relatively haphazard partly due to difficulties in accurately diagnosing the condition as well as fairly limited open surgical options for fixation and fusion of the joint.
Over the last 5 years there has been an explosion in minimally invasive and mini-open surgical techniques to treat symptomatic degenerative sacroiliac joint disease. One of these procedures is termed the DIANA procedure (Distraction Interference Arthrodesis with Neurovascular Avoidance).
Although the primary goal of the DIANA procedure is stabilisation of the sacroiliac joint, 90% of the procedure itself is actually performed in a large space behind the sacroiliac joint called the sacral recess.
The sacral recess contains multiple strong ligaments (interosseous ligaments) that bridge the gap from the iliac and sacral bones. These ligaments maintain the integrity of the sacroiliac joint and the integrity of connection between the iliac bone of the pelvis and the sacrum.
The DIANA procedure incorporates 4 separate components:
1. Complete exposure of the sacral recess– via a paramedian muscle-splitting incision. The recess is then emptied of soft tissue along this entire extent.
2 & 3. Distraction and fixation of the sacroiliac joint- the sacroiliac joint is indirectly distracted by distracting the medial (sacral) and lateral (iliac) boundaries of the sacral recess. To achieve this a guide pin is implanted using fluoroscopic control into the iliac bone of the pelvis. Positioning and trajectory of the guide pin is an essential component of the procedure and requires careful interpretation of fluoroscopic images performed in the antero-posterior (forward-backward), lateral and oblique planes.
Once the guide pin is positioned correctly and confirmed on the 3 fluoroscopic views, the sacral recess is progressively distracted using a series of progressively larger helical instruments until an appropriate degree of distraction of both the sacral recess and indirectly the underlying sacroiliac joint is achieved.
Once a satisfactory degree of distraction of the sacroiliac joint has been achieved, fixation of the distraction must then be obtained. This is achieved by implanting a DIANA screw sized to match the distraction obtained with the helical instruments.
4. Sacroiliac joint fusion- once the sacroiliac joint has been distracted and fixation of the distraction has been obtained by positioning of the DIANA screw, the exposed sacral recess and sacroiliac joint is then packed with bone graft. This component of the procedure is the most essential element of the whole surgery. The progressive development of a solid consolidated fusion mass within the sacral recess over the 6-9 month period after the surgical procedure maintains the distraction/fixation of the sacroiliac joint achieved with implantation of the DIANA screw and painful of the degenerative sacroiliac joint.