Introduction
The sacroiliac joint (SIJ) functions in transferring the load between the spine and the lower extremities and acts as a shock absorber for the spine. The structure is bordered by sacroiliac ligaments on both the anterior and posterior aspects. Many studies have associated the dysfunction of the SIJ as a source of back pain with the prevalence ranging from 10% to 38% of cases of low back pain. Conservative measures of treatment that can be considered include medications, activity modification, physical therapy, use of intraarticular steroid injections for pain relief, and radiofrequency ablation. In cases in which pain continues to persist despite conservative measures, surgical stabilization or SIJ fusion can be considered. Previously, SIJ fusion was conducted under open surgery with hardware placement. Various studies have shown that patients who underwent this procedure continued to have persistent severe pain at follow-up. Additionally, in an open fusion procedure, various pitfalls exist such as the length of the procedure, associated blood loss, length of hospitalization postoperatively, and increased levels of complications. In recent years, the development of a posterior approach to SIJ fusion with the use of cortical allograft placement and a drill-less method allows for a safer and more effective approach to SIJ fusion.
Anatomic considerations
In essence, the SIJs (SIJ) articulate both the sacrum and the ilium. SIJs are essential joints that aid in transferring the load between the spine and the lower extremities. Functionally, the SIJ acts as a shock absorber for the spine. The SIJ consists of a synovial joint and a syndesmosis, which are the intra- and extraarticular parts, respectively. The SIJ has a surrounding fibrous capsule with synovial fluid between the surfaces. Various ligaments exist around the SIJ, which at times may be sources of pain and inflammation. The sacroiliac ligament connects the sacrum to the ilium, and the posterior sacroiliac ligament connects the posterior superior iliac spine to the iliac crest to segments of the sacrum. Additional ligaments include the sacrotuberous ligament and the sacrospinous ligament. The sacrotuberous ligaments connect to the aforementioned posterior sacroiliac ligament, and the sacrospinous ligament originates in the ischial spine and attaches to the lateral aspect of the sacrum.
Various sources of blood supply to the SIJ exist. As for the blood supply, the internal iliac artery innervates the anterior aspect of the SIJ, and the superior gluteal artery can innervate the posterior aspect of the SIJ. Additionally, the median sacral artery and lateral sacral artery originate from the internal iliac artery and supply the SIJ.
As for the nerve innervation to the SIJ, research has shown that there is variability among different patients in the innervation of the SIJ. Despite the variability, in general, the innervation of the SIJ and surrounding ligaments is innervated anteriorly from the branches of the ventral rami of L4 and L5, branches of gluteal nerves, and the obturator nerve. In the posterior aspect, the innervation consists of the dorsal rami of S1 to S3 and the L5 dorsal ramus.
Patient selection and indications
Various selection indicators and indications exist for a patient to qualify for a posterior SIJ fusion. In general, for a patient to qualify for a posterior SIJ fusion, the patient must have history and physical examination findings of sacroiliitis, must have failed conservative management, and must have undergone a diagnostic local anesthetic SIJ injection. In general, the physical examination consists of various maneuvers (e.g., SIJ distraction test, the thigh thrust, the Gaenslen’s maneuver, the compression test, the FABER [flexion, abduction, and external rotation] test) to diagnose sacroiliitis, and diagnosis typically requires positive findings in three of five provocative maneuvers. Additionally, patients typically undergo a diagnostic SIJ injection to confirm that the source of pain is the SIJ. In this procedure, the patient undergoes the injection of local anesthetic via fluoroscopic guidance at the site of the SIJ to assess for greater than 50% pain relief. Additionally, patients with SIJ dysfunction typically have symptoms consisting of dull low back pain, sciatica-type symptoms, worsening pain with activity, an increased amount of pain in the morning, and muscle tightness in the bilateral hips or buttocks.
Contraindications
Various contraindications exist that may exclude a patient from undergoing an SIJ posterior fusion. Most important, patients who have not attempted conservative management with medications and physical therapy typically do not qualify for the procedure. Additionally, patients who may have insufficient pain relief from the diagnostic fluoroscopic-guided injection of local anesthetic to the SIJ do not qualify for SIJ fusion. Other contraindications to undergoing the procedure include any signs of systematic or spine infections, spinal malignancies, metastatic malignancy, pregnancy, and increased risk of bleeding caused by bleeding disorders.
Description of the procedure
Various procedure methods have been described to conduct a posterior SIJ fusion. In the procedure, the patient typically lies down prone under a fluoroscopy machine. Before the start of the procedure, all the instruments shown in Figure 7.1 should be confirmed, including the Steinmann guide pin, implant inserter, joint decorticator, outside dilator, and inside dilator. A 22-gauge needle is used to administer local lidocaine before starting the procedure. After successful local anesthetic administration, a 2- to 3-cm stab incision is made along the skin. After the incision is made, the Steinmann pin is advanced into the anterior cortical line of the SIJ as seen in Figures 7.2 and 7.3 in the lateral and anteroposterior views, respectively, and schematically in Figure 7.4 . After proper placement of the pin under fluoroscopic guidance, the inside dilator is slid into the outside dilator, and the dilators are advanced down the Steinmann pin until localized to the SIJ as seen in Figures 7.5 and 7.6 . After proper advancement, the internal dilator is removed, and a decorticator (see Fig. 7.1 ) is placed at the site of the outside dilator and advanced with the use of a mallet as seen in Figures 7.7 and 7.8 . After proper placement of the decorticator is confirmed under fluoroscopy, the decorticator is removed with the use of the mallet, and the allograft device is placed into the SIJ as seen in Figures 7.9 and 7.10 . After confirmation of the placement, all the devices are removed, and a final confirmation is done under fluoroscopy to confirm the placement of the allograft as seen in the lateral and anteroposterior views in Figure 7.11 . After confirmation, irrigation of the incision is conducted, and 2-0 Vicryl sutures are used for the closure of the open wound with dressing applied at the incision site.
