Establishing a Diagnosis

Goldthwaite and Osgood, in 1905, first described “sacroiliac strain” as a possible source of low back pain¹ and the sacroiliac joint (SIJ) was considered the primary source of low back pain in the early 20th century.² In 1936, Pitkin and Pheasant described lower extremity pain as originating in the sacroiliac and lumbosacral joints and their accessory ligaments and coined the term sacroarthrogenic telalgia. SIJ fusion became the treatment of choice for radicular pain originating from the low back.³ It was not until Mixter and Barr that focus was placed on the lumbar spine, the intervertebral disc, and the herniation of nucleus pulposus contents.⁴ Today, there is a reemergence implicating the SIJ as a potential source of low back pain with an estimated prevalence among patients with low back pain of 18% to 30%.^5,6

Pathology of the SIJ has been documented in a variety of conditions; structural abnormalities, joint infections, metabolic and inflammatory disorders, and degeneration have all been implicated.⁷ SIJ dysfunction or SIJ syndrome is a condition in which pain localized to the SIJ cannot otherwise be explained by an identifiable pathological process (e.g., joint infection). Clinically distinguishing primary SIJ dysfunction from the other etiologies that overlap in pain referral patterns may be difficult. Much of the confusion regarding the diagnosis of SIJ dysfunction revolves around the inability to differentiate SIJ pain from pain that originates from surrounding structures. For example, discogenic and facet joint pathology have a clinical presentation similar to that of SI joint pathology. Not only are the pain distributions considered similar in many references, but the clinical tests used in diagnosis (e.g., Patrick’s, Gaenslen’s) are known to stress surrounding structures.⁷ The familiar symptom in SIJ dysfunction is the pain or other symptoms ascribed to a rectangular area approximately 3 × 10 cm just inferior to the posterior superior iliac spine (PSIS) identified on a pain drawing; however, no clinical studies have demonstrated this as a consistent finding for diagnosing SIJ dysfunction.⁸ Through patient history and diagnostic testing, several referral patterns have been proposed, although these referral patterns may be present in other sources of low back pain.⁹

Furthermore, referral of pain into various locations of the lower extremity does not distinguish SIJ pain from other pain states.^5,10 However, only 4% of patients with SIJ pain mark any pain above the L5 on self-reported pain drawings.¹⁰ The multiple patterns of SIJ pain referral zones may arise for several reasons: SIJ innervation is highly variable and complex; pain may be somatically referred from other primary osseous and ligamentous nociceptors such as the zygapophyseal joint, intervertebral disc, or adjacent structures (e.g., piriformis muscle, sciatic nerve, and L5 nerve root); and the referral pattern may be affected by intrinsic joint pathology and become active nociceptors.¹ Slipman et al¹¹ examined pain referral patterns in patients with SIJ dysfunction and reported that 94% of patients had pain radiating into the buttock, lower lumbar region (72%), lower extremity (50%), groin area (14%), upper lumbar region (6%), and abdomen (2%). In 28% of patients, the pain radiated distal to the knee, and 14% described foot pain (Fig. 15-1).

Fig. 15-1 Pain referral pattern from the sacroiliac joint. In descending order, the most common referral patterns extend from the darkest (low back and buttock) to the lightest regions (foot).

SIJ syndrome may occur acutely from trauma, sudden heavy lifting, prolonged lifting and bending, torsional strain, rising from a stooped position, a fall onto the buttock, or rear-end motor vehicle accident with the ipsilateral foot on the brake.¹ Characteristically associated with SIJ dysfunction include buttock pain caudal to the PSIS; pseudoradiculopathy with pain radiating to the posterolateral aspect of the thigh (at times caudal to the knee); and aggravation of pain in sitting position, rising from a sitting position (exiting an automobile), and relieved by changing positions. The most consistent factor for identifying patients with unilateral SIJ pain is unilateral pain localized predominantly below the L5 spinous process.^5,7,8,10,12

Anatomy

The SIJ is the largest axial joint in the body, with an average surface area of 14 to 17.5 cm².^25,26 It is a diarthrodial joint, with the anterior third being synovial and the remaining posterior aspect a syndesmosis, composed of interosseous ligament connections (Fig. 15-2). An auricular-shaped joint oriented in an oblique medial to lateral direction, morphological variability exists in the adult SIJ with respect to size, shape, and surface contour.²⁷ The posterior aspect of the joint has a fibrous capsule but may lack synovial continuity with the anterior aspect of the joint. Designed for stability, the SIJ is a triplanar shock absorber, transmitting and dissipating upper trunk loads to the pelvis, force from the lower extremities during ambulation, and facilitates parturition. The SIJ rotates about all three axes, although the predominant motion appears to be x-axis rotation with some z-axis translation.¹ Motion of the SIJ is usually limited to 1 to 3 degrees of rotation and 1.6 mm of translation, with 90 percent of rotation occurring along the x-axis.¹ The SIJ motion progressively decreases, and motion at the joint may become markedly restricted secondary to increased cartilage; reduced density of chondrocytes, causing deep fissures in the cartilage; and fibrous connections among the auricular facets.²⁸ As the capsule becomes increasingly collagenous and fibrous, ankylosis occurs, and by the eighth decade of life, erosions and plaque formation are inevitable and ubiquitous.²⁹

Fig. 15-2 Sacroiliac joint and ligamentous structures.

Basic Science

Intraarticular structures possess nerve fibers, which are sensitive for pain and support the theory that nociceptive signals may originate from the intraarticular structures of the SIJ.³⁵ Additionally, as previously described, innervation exists for the SIJ, and the intraarticular nociceptive fibers and the lumbosacral innervation are intended for interventions. There is not a “gold standard” for the diagnosis of SIJ dysfunction, but the rationale for the use of SIJ blocks as standard for diagnosing SIJ pain is based on the fact that SIJs are richly innervated and have been shown to be capable of being a source of low back pain and referred pain in the lower extremity.³⁶

Therapeutic interventions in the treatment of SIJ pain include manual manipulation, prolotherapy, intraarticular injections, ablative procedures, and surgical interventions. Minimally invasive procedures, including intraarticular injections and ablative procedures, are minimally destructive to anatomy. Serial intraarticular injections of local anesthetics and steroids are thought to reduce the inflammatory response and the resultant joint symptomatology. Multiple studies have evaluated the effectiveness of intraarticular injections and ablative procedures (see Outcomes Evidence). Ablative procedures have included conventional radiofrequency (RF), pulsed RF (PRF) denervation, and cooled RF denervation of the SIJ. Conventional RF³⁷ and PRF³⁸ of the lateral branches have been reviewed and discussed by others.

The inherent challenge when treating patients with SIJ pain with RF energy is the inconsistent location of targeted lateral branch nerves.^39,40 The lateral branches supplying afferent information from pain-generating SIJs form a complex arcade of small nerve fibers anastomosing with multiple dorsal rami at each foramen. The location of these branches is unpredictable, varying from patient to patient, side to side, and level to level.³⁹ Additionally, conventional RF tissue ablation efficacy is limited by the lesion size secondary to impedance created by tissue desiccation, tissue boiling, and carbonization around the electrode tip. Carbonization is probably the most important cause of the increased impedance and leads to an abrupt decrease in lesion current (and delivered power), such that no more energy is delivered around the electrode and no additional tissue heating occurs.⁴¹ Cooled RF energy generates heat in the surrounding tissue, and internal cooling of the electrode moderates temperature near the tip (Fig. 15-3). Internal cooling enhances lesion size by removing the constraint of high-temperature charring in tissue adjacent to the electrode, thus allowing effective ionic heating at a greater distance.⁴²

Fig. 15-3 Isotherm probe and temperature moderation.

Imaging

No imaging studies consistently provide findings that are helpful to diagnose primary SIJ pain. Computed tomography (CT), magnetic resonance imaging (MRI), and bone scan are done predominantly to exclude other causes of pain rather than to diagnose idiopathic SIJ pain.⁹ Because of limitations of the history, physical examination, and imaging modalities, controlled fluoroscopically-guided or CT-guided, contrast-enhanced injections may be the only methods for definitively diagnosing or excluding the SIJ as a source of pain.⁹

The SIJ has several unique anatomical features that make it one of the more challenging joints to image. The joint is difficult to profile well on radiographic views, and therefore the radiographic findings of sacroiliitis are often equivocal.⁴³ MRI without and with intravenous gadolinium is currently the recommended modality for imaging patients with clinically suspected sacroiliitis and negative or equivocal radiographic findings.⁴³ MRI does not use ionizing radiation, but CT typically uses 1 to 2 rad compared with 0.5 rad for an anteroposterior (AP) radiograph,⁴⁴ and MRI can detect edema and enhancement before bone changes are visible on CT. MRI is also helpful in identifying active disease and following therapy response in patients with moderate and severe radiographic changes;⁴³ however, CT is superior to MRI for diagnosing chronic bone changes in the superior ligamentous aspect of the SIJ.⁴⁵ Imaging for diagnostic and therapeutic SIJ injections and lateral branch blocks (LBBs) requires fluoroscopic guidance, but ultrasound guidance has been used with varying success.^46,47 In SIJ RF neurotomy, radiographic assistance is necessary for placement of lesioning probes.

Guidelines

SIJ injections with local anesthetic and steroid serves as a diagnostic tool and therapeutic intervention. LBBs may serve as diagnostic or prognostic procedures, for lateral branch denervation. As previously stated, controlled fluoroscopically-guided or CT-guided, contrast-enhanced injections may be the only methods for definitively diagnosing or excluding the SIJ as a source of pain. Analgesic response to a diagnostic block serves as a method to diagnose SI joint pain; however, it is imperative that before performing an SIJ injection that proper history, symptom presentation, physical examination, and imaging studies are reviewed to assess the SIJ as a pain generator and other structures as a mimicker of SIJ pain. Single diagnostic blocks carry a false-positive rate of 20%⁶ and 22%,⁴⁸ so it is imperative to assess every patient for a true positive response and not the other factors contributing to analgesia or as a pain generator. These factors may include the placebo effect, convergence and referred pain, neuroplasticity and central sensitization, expectation bias, unintentional sympathetic blockade, systemic absorption of local anesthetic, and psychosocial issues.⁸

Guidelines for diagnostic and therapeutic treatment of SIJ dysfunction with injections at the SIJ and SIJ RF neurotomy has been proposed (Boxes 15-2 and 15-3).²⁴

Box 15-2 Criteria for Diagnostic and Therapeutic Sacroiliac Joint Injections

In the diagnostic phase, a patient may receive two procedures at intervals of no sooner than 2 weeks.

In the therapeutic phase (after the diagnostic phase is completed), the suggested frequency is at least 2 months between injections, provided that >50% relief is obtained for 6 weeks.

If the procedures are done for different joints, they should be performed at intervals no sooner than 2 weeks. It is suggested that therapeutic frequency remain at least 2 months for each joint. It is further suggested that both joints be treated at the same time, provided the injections can be performed safely.

In the treatment or therapeutic phase, the interventional procedures should be repeated only as necessary according to the medical necessity criteria.

Under unusual circumstances with a recurrent injury, procedures may be repeated after stabilization in the treatment phase.

Box 15-3 Selection and Exclusion Criteria for Sacroiliac Joint Neurotomy

Selection Criteria

Predominantly axial pain below the L5 vertebrae

Greater than 80% pain relief from two separate intraarticular blocks with no more than 2 cc of injectate per block. It is recommended to use higher concentration anesthetic such as 0.75% bupivacaine or 4% lidocaine for a more effective block.

Chronic axial pain lasting for >6 months

Age older than 18 years

Failure to achieve adequate improvement with comprehensive nonoperative treatments, including but not limited to activity alteration, NSAIDs, physical or manual therapy, and fluoroscopically-guided steroid injections in and around the area of pathology.

All other possible sources of low back pain have been ruled out, including but not limited to the intervertebral discs, the zygapophyseal joints, the hip joint, symptomatic spondylolisthesis, and other regional soft tissue structures.

Exclusion Criteria

Pregnancy

Systematic infection or localized infection at the anticipated introducer entry site

History of coagulopathy or unexplained bleeding

Irreversible psychological barriers to recovery

Active radicular pain or radiculopathy

Immunosuppression

NSAID, nonsteroidal antiinflammatory drug.

Indications and Contraindications

Selecting appropriate candidates for interventional pain medicine procedures is important, and SIJ RF neurotomy is no exception. Conservative treatment should be used before interventional treatments are initiated. These include nonsteroidal antiinflammatory drugs, physical therapy, manual manipulation, and other modalities addressing dysfunction at the joint. Interventional strategies include intraarticular joint injections, lateral branch nerve blocks, and denervative or ablative procedures. The ideal candidates for intraarticular injections include patients with known SIJ dysfunction, failed conservative therapy, or positive physical examination findings on more than two provocative maneuvers that stress the SIJ and ligaments. Contraindications for intraarticular injections include patient refusal, infection at the site of injection, history and physical examination finding inconsistent with sacroiliac etiology, and lack of imaging modality.

Indications for sacral joint RF neurotomy include axial low back or buttock pain lasting longer than 3 to 6 months, tenderness overlying the SIJ, positive physical examination findings on more than two provocative maneuvers that stress the SIJ and ligaments, failure to respond to conservative therapy, pain attenuation upon SIJ corticosteroid injections, or pain relief with LBBs at L4 and L5 primary dorsal rami and at S1-S3. Cohen et al⁴⁹ examined outcome predictors for RF denervation of the LBB and reported that no single variable strongly predicted outcome, suggesting that most patients with SIJ pain, irrespective of cause, can potentially benefit from the procedure.

Equipment

Sacroiliac Joint Injection

Preparation kit, sterile gloves, surgical cap and mask, 22-gauge 3.5-inch spinal needle, extension tubing

Fluoroscope

Medication

• Lidocaine 1%

• Contrast media (e.g., iohexol)

• Bupivacaine 0.5%

• Depo-methylprednisolone 40–80 mg (or equivalent)

Lateral Branch Block

Preparation kit, sterile gloves, surgical cap and mask, 22-gauge 3.5-inch spinal needle, extension tubing

Fluoroscope

Medication

• Lidocaine 1%

• Contrast media (e.g., iohexol)

• Bupivacaine 0.5% or ropivacaine 0.5%

Cooled Radiofrequency Sacroiliac Joint Neurotomy

Preparation kit, sterile gloves, surgical cap and mask, sterile surgical drape, 27-gauge 3.5-inch spinal needle, extension tubing

Fluoroscope

Grounding pad

Baylis Pain Management Generator, Pain Management Pump Unit, Pain Management Cooled Radiofrequency Connector Cable, Pain Management SInergy Probe, Pain Management SInergy Introducer, Pain Management Tube Kit, Pain Management Epsilon Ruler

Medication

• Lidocaine 1%

• Bupivacaine 0.5%

• Contrast media (e.g., iohexol)

• Depo-methylprednisolone 40–80 mg (or equivalent)

Technique

Sacroiliac Joint Injection

Fluoroscopy guidance is recommended and is described. The patient is placed on the fluoroscopy table in the prone position. After sterile preparation and drape have been accomplished, an AP fluoroscopic image of the SIJ is obtained. The fluoroscope is angled caudad, placing the PSIS and iliac crest overlying the joint image. The fluoroscope is obliqued to the contralateral side (20 to 30 degrees), placing the anterior and posterior aspect of the joint in line. A point along the inferior third of the joint is the target for injection. This area is anesthetized, and a 22-gauge spinal needle is advanced under coaxial technique and intermittent fluoroscopy until the joint has been entered; adjustment should be made accordingly. Entrance into the joint experienced as lack of ease to withdrawal the needle and arcing of the needle along the curvilinear joint and is confirmed by delivery of radiopaque contrast showing an arthrogram indicating intraarticular spread of contrast (Fig. 15-4). A solution containing local anesthetic and steroid is delivered showing spread of the residual intraarticular contrast. The needle is retracted from the joint, subcutaneous tissue, and skin.

Fig. 15-4 Right sacroiliac joint arthrogram.

Cooled Radiofrequency Sacroiliac Joint Neurotomy

The patient should be NPO (nothing by mouth). Bowel preparation is optional, and prophylactic antibiotics can be administered based on physician preference. This is a minimally invasive procedure, and monitored anesthesia care is adequate sedation during the procedure.

Identifying Target

The patient is positioned prone, and sterile prep and surgical drape are applied. An AP fluoroscopic image is obtained of the sacrum, including the intervertebral space at L5-S1. The endplate at S1 is aligned, reducing parallax at the first target (L5 dorsal ramus). The target location is the notch between the ala of the sacrum and the superior articular process (SAP) of the sacrum. The target for the S1-S3 levels is the lateral aspect of the sacral foramina.

Needle Placement

For the L5 dorsal ramus, needle placement is not necessary, and the introducer cannula is advanced without prior needle placement. The puncture point on the skin is just lateral and inferior to the target. The introducer is advanced until contact is made with the periosteum (Fig. 15-5). In the AP fluoroscopic view, the tip of the needle should be immediately adjacent to the base of the SAP and under its lateral margin. A lateral view is obtained to confirm depth of needle placement. The most ventral extent of the cannula in lateral view should be the zygapophyseal joint (Fig. 15-6). The stylet is removed, and bupivacaine 0.5% or lidocaine 2% can be delivered but is optional before lesioning. The SInergy probe is placed through the introducer cannula. The probe is 2 mm shorter than the stylet and will seat in the cannula 2 mm off of the dorsal sacral surface. Displayed on the pain management generator, impedance should not exceed 500 ohm. Impedances greater than 500 ohm may indicate that the probe is seated in tissue not suitable for lesioning or that the probe is not fully seated in the hub of the introducer cannula. The “skin stopper” is advanced along the shaft of the introducer cannula to serve as a depth marker, ensuring that the cannula and probe are not inadvertently advanced.

Fig. 15-5 L5 dorsal ramus target and probe insertion. SAP, superior articular process.

Fig. 15-6 Lateral view of probe placement. Note that the cannula and introducer are initially placed to the zygapophyseal joint.

The lateral branches at S1-S3 are approached by raising a skin wheal over the skin entrance sites and subcutaneous tissue with lidocaine 1% to 2% toward the lateral aspect of S1-S3 dorsal sacral foramina. The 25- and 27-gauge spinal needles are advanced to the lateral aspect of the dorsal sacral foramina. These needles function as reference points for the placement of the introducer and probe in the absence of reliable osseous structures. A lateral fluoroscopic view is obtained to confirm entrance of the dorsal sacral foramina canal (Fig. 15-7).

Fig. 15-7 Left S1-S3 finder needle placement at the lateral aspect of the dorsal sacral foramina with entrance of the dorsal sacral canal.

Probe Placement

In the AP view, the Epsilon ruler is placed on the skin overlying the sacral foramina. The S1, S2, and S3 levels should have the Epsilon ruler placed with the central spoke aligned with the lateral border of the S1, S2, and S3 foramina, which is marked by the previous needle placement. The ruler is rotated around the central spoke axis such that the upper spoke is marking a location at a 2 : 30 position (right side) or 9 : 30 (left side).

The first target for the introducer cannula placement is the 4 : 00 position for the right side and 8:00 for the left side (Fig. 15-8). Using coaxial technique and intermittent fluoroscopy, the cannula is advanced until the stylet has made contact with the dorsal sacral surface. A lateral fluoroscope view is obtained to confirm depth and contact with the dorsal surface and is not transforaminal. The stylet is removed, and bupivacaine 0.5% or lidocaine 2% can be delivered but is optional before lesioning. The SInergy probe is placed through the introducer cannula. The probe is 2 mm shorter than the stylet and will seat in the cannula 2 mm off of the dorsal sacral surface. Displayed on the pain management generator, the impedance should not exceed 500 ohm. The “skin stopper” is advanced along the shaft of the introducer cannula to serve as a depth marker, ensuring that the cannula and probe are not inadvertently advanced into the foramen. The same sequence is used to place SInergy probes at the 2:30 position and the 5:30 position for the right side (9:30 and 6:30 for left) at the S2 level. The S3 level varies in that two lesions are created by placing probes at 2:30 and 4:00 for the right side and 9:30 and 8:00 for the left side (Fig. 15-9). Because simultaneous lesions cannot be created with the present pain management generator, the sequence is repeated for each probe placement.

Fig. 15-8 Left S1 and S2 epsilon ruler placement and introducer placement at the 8:00 position (right 4:00 position).

Fig. 15-9 Left L5 and S1-S3 probe placement. Foramina (purple). The lesion targets or lateral branch denervation sites (orange) are the areas of probe placement.

Lesioning

The standard lesion parameters are set in the pain management generator. The set temperature is 60° C with a total lesion time of 2:30 minutes. Lesioning is initiated by pressing the output on/off button. Upon pressing the output on/off button, lesioning will begin after priming of the circuit is complete. The pain management generator will shut off when lesioning is complete. After each probe placement, the lesion sequence will be initiated.

Patient Management and Evaluation

Postprocedure instructions are presented in Box 15-4. A benchmark for successful treatment of SIJ pain has been reported in the literature as a 50% reduction on visual analog scale (VAS) scores from baseline.⁴⁰ Patients should be evaluated within 4 weeks for efficacy and complications. If bilateral neurotomies are indicated, the contralateral side can be lesioned 7 to 10 days after the initial procedure.

Box 15-4 Postprocedure Instructions

Do not drive or operate machinery.

Do not engage in any strenuous activity.

Do not soak in the bathtub, but a shower is okay.

Bandages may be removed the following day.

Resume normal activities as tolerated the day after the procedure.

Avoid excessive activity, lifting, and other forms of increased physical activity for 1 to 3 days after the procedure.

If you experience fever, chills, or severe pain accompanied by swelling and redness at the injection site, contact your treating physician.

If you experience shortness of breath or chest pains, go to the nearest emergency department.

Outcomes Evidence

Cooled RF neurotomy for SIJ pain is novel procedure presently without substantial outcome evidence. Although a new technology, Kapural et al⁴⁰ in a retrospective study investigated cooled RF of the lateral branches. The primary outcome measures were pain relief (VAS scores), changes in function (pain disability index [PDI]), and global patient satisfaction (GPE). Improvements were observed in VAS pain scores 7.1 ± 1.6 to 4.2 ± 2.5 (P <.001) and PDI from 32.7 ± 9.9 to 20.3 ± 12.1 (P <.001) at 3 to 4 months after the procedure. Of 26 patients, 18 rated their improvement in pain scores using GPE as improved or much improved, and eight claimed minimal or no improvement. In a randomized placebo-controlled study evaluating lateral branch RF denervation, Cohen et al⁵⁰ used the numeric rating scale (NRS) as a primary outcome measure and Oswestry Disability Index (ODI) score, reduction in analgesic medications, and GPE as secondary measures. At 1 month, the treatment group had significantly lower NRS scores than the placebo group (2.4 ± 2.0; range, 0 to 8 vs. 6.3 ± 2.4; range, 2 to 10; P <.001). One, 3, and 6 months after the procedure, 11 (79%), nine (64%), and eight (57%) RF-treated patients experienced pain relief of 50% or greater and significant functional improvement. The authors concluded L4 and L5 primary dorsal rami and S1-S3 lateral branch RF denervation may provide intermediate-term pain relief and functional benefit in selected patients with suspected SIJ pain.

Risk and Complication Avoidance

Fluoroscopic guidance and a firm grasp of anatomy are paramount to performing this procedure safely and effectively. Reported complications from the procedure include temporary worsening of pain attributed to procedure-related pain or temporary neuritis^50,51 and temporary, self-limiting (<14 days) paresthesias.^49,51 Before lesioning, corticosteroid delivery may attenuate the symptoms secondary to neuritis.⁵²

The placement of the introducer cannula and subsequent probe should be confirmed using multiplanar fluoroscopy. At the L5 dorsal rami, the cannula should be directed at the dorsal surface of the notch between the sacral ala and the SAP of the sacrum. The most ventral extent of the cannula in lateral view should be the zygapophyseal joint. At the sacral levels (lateral branch), the probe should be placed such that the active tip is at least 7 mm from the edge of the nearest posterior sacral foramina. The practitioner should verify in lateral fluoroscopic view that the probe is dorsal to the sacral surface and not in the sacral foramen.

Conclusion

The SIJ is a reemerging yet underappreciated potential source of axial low back pain. Historically, individual physical examination maneuvers have proven equivocal in diagnosing SIJ dysfunction, but combinations of physical examination maneuvers and the use of image-guided local anesthetic diagnostic blocks increase the likelihood of diagnosis and prognosis of therapeutic procedures such as ablative procedures. Using cooled electrodes has shown promise in the treatment of refractory cases of SIJ pain compared with conventional RF procedures. The cooled electrodes create a larger legion by overcoming impedance created by tissue desiccation, tissue boiling, and carbonization around the electrode tip. Although long-term studies are lacking, the promise of this modality has implications not only for treating patients with SIJ dysfunction but additionally in the treatment of those with pain originating from the zygapophyseal joints.