sacroiliac joint disease. Yet, even the sacroiliac joint injection has been shown to be not very reliable. The effects of two consecutive injec­tions are identical only 60 % of the time. One possible explanation for the inaccuracy of the sacroiliac joint injection is the diffusion of the anesthetic agents out of the sacroiliac joint dur­ing injection. The diffusion causes the anesthetic agents to come in contact with adjacent nerve trunks or roots, which leads to temporary pain relief even if the sacroiliac joint may not be the sources of pain. Injection of the anesthetic agents into the sacroiliac joint might relieve pain from numerous surrounding ligaments as well.

When conservative treatment fails to relieve pain from suspected sacroiliac joint disease, fusion surgery becomes a treatment option. Various open fusion surgery techniques have been developed including the posterior or Smith­Petersen approach, the anterior approach, and the posterior midline fascia splitting approach [ 4 , 14 ]. The results from the open sacroiliac joint fusion surgeries were mixed. Some reported great effi cacy, yet some results were disappoint­ing. In one study by Schutz et al., the nonunion rate with instability was 41.2 %, and more than 80 % of the patients still had signifi cant pain after the surgery [ 21 ]. The open surgery itself is usu- ally painful due to the extensive dissection needed for the surgery. The relatively high com­plications and nonunion rates of open surgeries encourage surgeons to search for alternatives with possible lower morbidities and higher effi cacy.

In 2008, Wise and Dall described a minimally invasive sacroiliac joint fusion procedure and published their series of 13 consecutive patients [ 26 ]. All the patients had no relief after more than 6 months of conservative therapy and completed exhaustive workups to rule out lumbar spine as the source of pain. A fl uoroscopically guided intra-articular injection with a mixture of local anesthetic and corticosteroid was used to confi rm the diagnosis of sacroiliac joint dysfunction. Their surgical technique involved inserting cages along the anterior-posterior (AP) axis of the sac­roiliac joint percutaneously. The key for safe placement of the cages in the AP axis was the understanding of the safe cephalad and caudad margins of the sacroiliac joints and the depth of placement based on preoperative images. It is important to avoid placing the cage too deep through the anterior portion of the joint and into the pelvis. Preoperative CT scans of the bilateral sacroiliac joints with the patients in the prone position (same position as in the surgery) were used to determine the area with the most bony surface available on both sacral and iliac sides of the joint as the “safe zone” for cage placement. During surgery, with the patient in prone posi­tion, the starting point of the incision was made on the most prominent part of the posterior supe­rior iliac spine (PSIS) and extended 1 cm caudad and 4 cm cephalad. The dissection was carried down to the PSIS, and a calibrated Steinman pin was tapped into the bone carefully. The place­ment of the Steinman pin was approximately 6–7 mm cephalad to the caudal margin of the safe zone. The depth of the Steinman pin advance­ment was carefully monitored using fl uoroscopy so that it was within the preoperative measure­ments (usually between 4.5 and 6.5 cm). When the pin was at the predetermined position, a 9-mm cannulated drill was used to drill over the pin. The surgeon watched the lateral fl uoroscopic

4.6 postoperatively. The mean ODI dropped from 59 to 45. The mean patient satisfaction was 6.8, and all the patients stated that they would undergo the same procedure again under the same circum­stances. Placing the anchoring screws across the sacroiliac joint may have the benefi ts of immedi­ate stabilization, before the fusion happens. Although the posteriorly placed grafts into the AP axis of the SI joints like the ones used by Wise and Dall may have the same effect function­ing as a door wedge stabilizing a pivoting door.