Introduction
Sacroiliac joint (SIJ) pain is one of the most common causes of axial low back pain. Studies have shown that 13% to 30% of chronic axial low back pain is related to the SIJ. This wide variability of reporting is related to the methodology used to confirm the diagnosis. Innervation of the SIJ is variable with most literature reporting S1 to S3 lateral branches as the main nerve supply with contribution from the L5 dorsal ramus and possible innervation from the L4 medial branch and S4 lateral branch ( Fig. 4.1 ). Administration of local anesthetic to the L5 dorsal ramus and the lateral branches of S1 to S3 has been described as a diagnostic tool before denervation of the SIJ. These blocks have a predictive value for positive outcomes after radiofrequency ablation (RFA) for treatment of patients with chronic SIJ pain.
Indications
Sacral lateral branch nerve block is usually done as a diagnostic test before denervation of the SIJs for long-term pain relief. It has a more predictive value for favorable outcomes after RFA than intraarticular or periarticular injection.
Contraindications
Contraindications to the diagnostic sacroiliac joint, sacral lateral branches nerve block:
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Systemic or local site infection
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Anticoagulation (relative)
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Allergy to medications
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Patient refusal
Diagnosis
The diagnosis depends mainly on history and physical examination. Patients commonly report pain with transitional activities such as rising from a seated position or getting out of bed. Pain is described as unilateral or bilateral pain below the belt line with occasional radiation along posterior thigh to the ipsilateral knee (pseudo-radiculopathy). International Association for the Study of Pain diagnostic criteria include a positive Fortin finger test result (pain within 1 cm inferior-medial to the posterior superior iliac spine), three or more positive provocative test results (Faber, Gaenslen, compression, distraction, and so on), and pain that is relieved by injection of the SIJ with the latter reported to be the most specific tool.
Radiologic findings can help confirm the diagnosis and vary from SIJ sclerosis to significant degenerative changes.
Procedure
The patient is positioned in the prone position with a C-arm in either an anteroposterior (AP) or with a slight cephalocaudal angle to optimize appearance of sacral foramina. The patient’s legs and heels are abducted to prevent tightening of the gluteal muscles, which can obscure the view of the sacrum. A wide prep is then completed with an antiseptic solution. Lidocaine 1% is then used to anesthetize the skin. A 22- or 25-gauge spinal needle is advanced under fluoroscopic guidance to the location of the ipsilateral L5 dorsal ramus using the AP and oblique views (L4 could be completed if desired; Fig. 4.2 ). The 22- or 25-gauge spinal needles are then advanced to a point approximately 5 mm lateral to the ipsilateral S1, S2, and S3 sacral foramina, corresponding to the pathway of the lateral branch nerves at S1 to S3 ( Fig. 4.3 ). After the position of the needles is confirmed, a lateral fluoroscopic view is obtained to ensure adequate depth. After negative aspiration of blood and cerebrospinal fluid, 0.5 mL of 0.5% bupivacaine is injected at each level.
