The sacroiliac (SI) joint can be a significant source of low back pain (141–143). Etiologies of SI pain include spondylo arthropathy, crystal arthropathy, septic arthritis, trauma, and pregnancy diasthesis (144). In addition, SI joint dysfunction (pain from a biomechanical disorder without a demonstrable lesion) has been proposed as a possible etiology of SI pain (145). Among patients with chronic low back pain, a study using a single block technique of the SI joint with a local anesthetic, estimated the prevalence of SI joint pain as between 13% and 30% (141). A study on 54 patients with unilateral low back pain suspected from the SI joint, using a dual local anesthetic block technique, demonstrated an 18.5% prevalence of SI joint-based pain (142).
Anatomy and Pathophysiology
The SI joint is a true diarthrodial joint and is innervated by nerves from the L4 through S2 levels (146). Studies on human and animal SI joint capsules demonstrated the presence of mechanoreceptors and nociceptors (147,148). The SI joint has a close anatomic relationship to the lumbosacral plexus and the L5 and S2 nerve roots. Therefore, SI joint pathology such as inflammation or chronic synovial irritation from joint dysfunction can not only serve as a pain generator, but also can potentially involve the nearby neural tissues and induce pain. Injection of the joint with contrast material in healthy volunteers produced pain that extended approximately 10 cm caudally and 3 cm laterally from the posterior superior iliac spine in a linear strip (146). Patients with pain diagrams similar to the SI joint pain mapping were confirmed as having SI pain with SI joint provocation injection (149).
Diagnosis of the SI Joint Pain
The value of clinical data from history and physical examination in the diagnosis of SI joint pain remains controversial (141–143,150,151). Although SI joint pain frequently manifests as pain in the sacral sulcus areas, SI joint pain can refer to the buttock, lower lumbar region, groin, and lower limb (152). However, none of these symptoms, signs or various provocative tests are pathognomonic for SI joint pain. Other sources of low back pain, such as lower lumbar Z-joint arthropathy or degenerative disc disease, can present similarly. By using fluoroscopically guided SI joint blocks to confirm cases of SI joint pain (Fig. 68-17), several authors have shown that clinical medical history and pain provocation tests are not reliable in the diagnosis of SI joint pain (141–143,150,151).
FIGURE 68-17. AP view of right SI joint arthrogram demonstrating contrast in the posterior (medial) and anterior (lateral) joint space. This 23-year-old man complained of persistent right-sided low back pain after a front-impact motor vehicle collision. He was forcefully pressing his right foot on the brake during the collision, with resultant right SI pain. Injecting the right SI joint with 1 mL of 2% lidocaine relieved 90% of his low back pain, lasting several hours. SI joint injections can have both diagnostic and therapeutic benefits.
In a clinical trial involving 84 patients with possible low back pain from the SI joint, Dreyfuss et al. studied clinical history and the 12 physical examination tests deemed most reliable by a panel of experts for isolating SI joint pain (143). Fluoroscopically guided intra-articular SI joint injections of local anesthetic and corticosteroid were performed to confirm the diagnosis. The criterion for a positive result was the achievement of at least 90% pain relief postinjection. The study demonstrated that neither the history nor the physical examination data was of significant value in diagnosing SI joint pain (141). Maigne et al. investigated 54 patients with clinical features of chronic low back pain compatible with the origin in the SI joint with the following features: unilateral buttock pain, tenderness over the SI joint, normal lumbar CT scan, failure of previous epidural, or facet injections (142). They applied seven “SI pain provocation tests” before and after the dual block of SI joint. To be considered diagnostic, patients had to report 100% pain relief after block with 1% lidocaine and at least 75% pain relief after block with 0.25% marcaine. There was an 18.5% rate of positive responders to this dual block. The result demonstrated that none of the SI joint pain provocation tests were able to isolate SI joint pain (142). Slipman et al. performed a diagnostic fluoroscopically guided SI joint injection in 50 consecutive patients with low back pain presumed to be from SI joint (162). A reduction of the VAS rating by at least 80% was considered a positive response to SI joint block. The authors concluded that the various SI joint provocative maneuvers were not useful in diagnosing SI joint pain (162). A diagnostic imaging study done with bone scan was found to have low sensitivity and high specificity for diagnosing the SI joint syndrome (149). This study excluded patients with SI joint pain from inflammation, such as in a seronegative spondyloarthropathy. However, another study using single photon emission CT (SPECT) was performed in 54 patients with symptoms of low back pain of at least 3 months duration, the presence of higher erythrocyte sedimentation rate, and higher C-reactive protein levels who had not received anti-inflammatory drugs. The results demonstrated high sensitivity (97%) and specificity (90%) in diagnosing inflammatory disease within SI joints (153).
Although exact guidelines for administering an SI joint injection are unclear, one set of guidelines is as follows: a diagnostic SI joint injection is indicated in patients with pain over the sacral sulcus who have failed to respond to 4 to 6 weeks of directed physical therapy and oral nonsteroidal anti-inflammatory agents (154,155).
The patient is placed in a prone position. The skin over the sacral area is prepped and draped in a sterile manner. By rotating the C-arm fluoroscope slightly contralaterally, but occasionally ipsilaterally, intermittent fluoroscopy is used to identify the medial joint line when it just separates from the lateral joint line of the SI joint. Some adjustment of the C-arm in the caudal or cephalad plane may then be used to best isolate and visualize the lower portion of the SI joint. The targeted area is the small lucent area just below the joint line. The skin entry site is selected slightly lower than the targeted area, and is infiltrated with a small amount of 1% lidocaine. A 22- or 25-gauge 2.5 to 3.5-in. spinal needle is inserted and directed down to contact the ilium. The needle is then withdrawn 2 to 3 mL and redirected toward the inferior-medial aspect of the joint into the lucent area (156). Typically, the needle tip will bend if it enters the SI joint, and a tactile sense of a sliding into the joint will be appreciated (157). Applying a slight curve at the tip of the needle prior to use may help assist this process (156). A small amount of contrast is then injected to outline the SI joint. If the needle fails to plunge and no contrast flow is seen on fluoroscopy, one technique advocates that the needle be slowly extracted a millimeter at a time, while continuing to maintain pressure on the plunger until there is a loss of resistance (157). Once an SI joint arthrogram without a vascular uptake pattern is demonstrated, anesthetic with or without steroid is injected (depending upon if the injection intent is for therapeutic or diagnostic use, respectively). One milliliter of 2% lidocaine or 0.5% bupivacaine mixed with 40 mg/mL of triamcinolone acetonide, or other equivalent corticosteroid, is injected into the SI joint (158–161). A total of no more than 2.0 mL of volume is generally injected due to the limited volume of the SI joint (160).
Diagnostic Injection of SI Joints
Because the gold standard for proof of SI joint pain is unclear, the sensitivity and specificity of diagnostic SI joint injections has not been clearly established.
Maigne et al. (142) have suggested that the SI joint block has diagnostic value only for pain from intra-articular sources, not for SI joint pain from extra-articular sources such as the periosteum, interosseous ligaments, erector spinae muscles, or fascial elements, all of which contain nociceptors and hence are possible pain generators (147,148). Therefore, an SI joint block procedure that involves injection of an agent into the extra-articular components rather than the joint cavity may show better correspondence to the clinical features. Future studies should address whether the combination of pericapsular and intra-articular SI joint injection with corticosteroid can improve outcomes.
Therapeutic Injection of the SI Joint
The efficacy of SI joint corticosteroid injections has been reported in prospective and retrospective studies of patients with spondyloarthropathy (163,164). In a retrospective study, Slipman et al. reported a significant benefit from SI joint steroid injection in patients with SI joint syndrome (165). Thirty-one patients with chronic SI joint syndrome received an average of 2.1 fluoroscopic-guided SI joint corticosteroid injections. The average follow-up was 94.4 weeks. Of the 29 patients who completed the study, there was a significant improvement in the Oswestry disability score, VAS, and work status (165). Although these retrospective results are encouraging, there are currently no prospective studies on the efficacy of fluoroscopically guided therapeutic SI joint corticosteroid injections.
Radiofrequency Ablation of the SI Joint
Radiofrequency ablation (RF-A) has recently been proposed as a potential long lasting treatment for SI joint pain, and has been gaining more popularity along with other nonsurgical spinal procedures. RF-A involves de-innervation of the SI joint nerves believed to be responsible for generating pain (166,167). It is indicated as a treatment for those patients who have failed more conservative measures, yet only received transient benefit from diagnostic and/or therapeutic injections of the SI joint (168). The true effectiveness of RF-A of the SI joint is unclear, as of yet (169). In contrast to RF-A in treating lumbar spine facet-mediated pain, which directly targets the medial branches of the dorsal rami, which innervate the facet joints (170), the SI joint has complex innervations (171). Therefore, no consistent procedural technique has been described in the literature. Multiple studies have, in fact, been done using various techniques for RF-A of the SI joint, which are summarized in Table 68-6. The table shows that there are variations among the techniques used in regard to structures, nerves, and patterns of ablation to the SI joint.
The table underscores the fact that there is no standard pattern of ablation and not enough available prospective data to determine which rami or branches should be ablated, or if a pattern technique (i.e., “leap frog” vs. “strip lesion”) is more efficacious. The studies do not show uniformity and additional studies to determine if RF-A is useful for treating chronic SI joint pain are warranted.