Position and anatomical landmarks
The patient lies in the prone position on the operating table with a pillow under the pelvis in such a way that the sacral bone is rotated in a ventral direction. In AP view, the medial SI joint line is formed by posterior articulation of the joint.
The C-arm is rotated contralaterally until the medial cortical line of the posterior articulation is in focus. Tilting the C-arm longitudinally in relation to the patient (cranially caudally) can sometimes help the pain specialist to distinguish between anterior and posterior articulations.
Needle insertion is 1-2 cm cranially from the lower border of the SI joint at the level of the zone of maximal radiographic translucency.
Introduction of the needle into the SI joint is characterised by a change in resistance. The tip of the needle often appears to be slightly curved between the sacral bone and iliac bone. On a lateral view, the needle tip should appear anterior to the dorsal border of the sacrum. Injection of contrast agent shows dispersal along the articulations as well as filling of the caudal joint capsule (Figures 1 and 2).
Figure 1. Intra-articular injection into the SI joint with contrast.
Only use 0.25-0.5 ml of contrast agent. If this technique is not successful, then approaching the joint from a more rostral insertion point, or using CT guidance, may facilitate penetration.
Figure 2. Intra-articular injection into the SI joint with contrast.
- Temporary paresis of the ischial nerve.
- Damage to the ischial nerve, lumbar and sacral nerve roots.
- Temporarily increasing pain.