Illustration of the posterior sacral ligaments: posterior superior iliac spine (1); iliolumbar ligament (2); interosseous and dorsal sacroiliac ligaments (3); sacrotuberous ligament (4); sacrospinous ligament (5). (Reprinted with permission from Dr. Danilo Janovic)
The SIJplays a causative role in up to 30% of patients with chronic low back pain. Afflicted patients will typically have back pain below the L5 level with radiation to the buttocks or lower extremities. Provocative physical exam tests can be used to identify likely candidates, and the findings of 3 or more positive tests have been found to have a modest predictive power (sensitivity 91%, specificity 78%) in relation to controlled comparative SIJ blocks. Key tests include distraction, compression, thigh thrust, Gaenslen’s, sacral thrust, and Patrick’s FABER. However, their ability to detect posterior complex pain has not been evaluated.
Probe: C5-2 MHz curved transducer.
Transverse Plane Scan
This is the primary view for procedures targeting the SIJ. Accurate identification of the various landmarks depends on a methodical scan which begins at the sacral hiatus and progresses cephalad to the posterior S1 foramen (Fig. 15.2).
Sagittal Plane Scan
This view is used for needle placement verification during SLB block procedures (Fig. 15.3).