SIJ RFN Review
J. Scott Bainbridge, MD
Back pain is a pervasive problem in the general population . The origin of this pain is not always well understood, and as a result of this, there is mixed evidence for many treatments. Living with chronic pain results in lost productivity, decrements in quality of life and substantial health care utilization, including the use of opiod medications, . RF Neurotomy, when provided to appropriate patients by trained providers, has been shown to alleviate back pain associated with the sacroiliac joint complex, [3-8].
The prevalence of sacroiliac joint generated pain amongst those presenting with axial low back pain varies, according to age, history of lumbosacral fusion, or other population features, between 15-40%. [9-17]
The sacroiliac joint is a synovial articulation with contoured surfaces covered in hyaline cartilage which is thicker on the sacral side. There is a fibrous capsule and very strong supporting ligamentous structures consisting of the anterior sacroiliac, posterior SI, and interosseous SI ligaments, and the sacrotuberous and sacrospinous ligaments. This construct allows for the absorption of great forces across the joint, and subtle movement with walking and other activities. 
The innervation of the SIJ is contentious [19, 20], with some postulating that it is innervated only dorsally [21, 22], while others [23, 24] believe the joint to be innervated both ventrally, via anterior rami, and dorsally, via the L5 dorsal rami and sacral lateral branches. The posterior capsule and dorsal ligamentous structures of the sacroiliac joint are innervated by pain sensitive nerve fibers [6, 21, 22, 24-26] arising from the L5 dorsal rami and sacral 1-3, but not the 4th lateral branches  Cadaveric studies have revealed the course of the sacral dorsal rami and lateral branches, [6, 27].
Dreyfuss, et al.  showed that multi-site, multi-depth lateral branch blocks, with green dye, were effective (91% accuracy) in staining the lateral branches, in a cadaveric study (2 cadavers; 4 joints). Subsequently 20 volunteers were shown to be able to experience pain with experimental stimulation of the dorsal SIJ ligaments, and with distention of the SIJ capsule. It was found that performing active L5DR and S1-3 LB blocks on 10 rendered 70% of the subjects insensate to dorsal ligament stimulation, but only 20% insensate to capsular distention. After saline (control) L5 DR and S1-3 lateral branch blocks the group (n=10) did not experience protection (anesthesia) from the experimental pain stimulus. This study demonstrated the results of sacral lateral branch blocks cannot be attributed to non-specific effects and they are adequately physiologically effective to be used clinically. This was not the case with the use of single site lateral branch blocks, .
Given the findings of Dreyfuss, and the fact that only the L5DR and lateral sacral branches can be safely denervated, it follows that those patients who receive pain relief with screening multi-site, multi-depth lateral branch blocks will be most likely to benefit from SIJ RFN. Based upon similar validated methodology when treating cervical and lumbar zygapophysial joint denervation, using two sets of confirmatory blocks should, in theory, be optimally predictive of a successful outcome following treatment with SIJ RFN.
Multiple researchers have studied clinical outcomes of the use of radiofrequency lesioning (RFL) techniques to treat sacroiliac joint complex pain. Patient selection methods for these studies have been variable, with many of the studies having been carried out before the publication of the multi-site, multi-depth lateral branch block technique noted above, . Likewise, various RFL techniques and technologies have been employed.
Burnham, et al  prospectively selected 9 patients through intra-articular SIJ block and confirmatory single-depth, multi-site lateral branch blocks. He used a bipolar technique and 33% experienced >50% relief at 6-9 months. Yin, et al  followed 14 subjects, who were selected for SIJ RFN through response of >70% relief of pain with dual interosseous ligament block with 5cc of 0.5% bupivacaine, for 6 months. RFN was carried out using curved, blunt, 20 guage needles with 10 mm exposed tips and sensory stimulation guided lesioning. Succesful outcomes, as defined by >60% subjective and >50% pain score reduction at 6 months, was reported in 64%. Furthermore, 36% reported complete relief of pain. Ferrante, et al’s outcomes following bipolar RF strip lesions along the joint line were poor, possibly related to patient selection and RFN methodology[6, 29, 30]. Kapural et al performed cooled RF on 27 subjects selected through two intra-articular SIJ blocks with >50% relief of pain. Two thirds experienced meaningful and statistically significant improvement in pain and function at 3-4 months post-procedure.  Karaman also selected patients who experienced at least 75% relief of pain with two SIJ blocks. Cooled RFN resulted in 80% of 15 patients reporting >50% pain reduction and 87% of those had > 10 point reductions of their ODI scores. 
Speldewinde made use of a palisade technique modified from the method described by Cosman, [5, 31]. 20 patients were selected for SIJ RFN through dual SIJ blocks with 80% relief, and 15 were available for follow up. 12 of 15 had >50% relief and 46% experienced 100% relief of pain.
Cohen, et al.  published results from a randomized, placebo controlled trial (RCT) of L4-L5 dorsal rami and S1-3 lateral branch (LB) radiofrequency neurotomies (RFN), using cooled probe technology, for the treatment of sacroiliac joint pain. Patients were selected based on > 75% relief of pain with each of two intra-articular SIJ blocks. 8/14 (57%) of those treated achieved >50% relief of pain and functional improvement at 6 months, whereas 0/14 of the placebo group (sham treatment) obtained that level of improvement. A statistically significant difference between groups was present for pain (NRS), Oswestry Disability Index, Global Perceived Effect, medication reduction, and percent with a “positive outcome”. There were no serious complications. Cohen’s outcomes were clinically significant and supportive of the procedure of SIJ RFN, despite his use of only intra-articular SIJ blocks for patient selection.
Patel and Gross  carried out a randomized (2:1), sham controlled, study of L5DR and S1-3 LB RFN on patients selected for inclusion through dual lateral branch blocks. The LBBs were done using a single site at the lateral margin of each sacral foramen, with injection of 0.5cc of local anesthetic. A successful outcome was defined as > or equal to 50% reduction in pain score, corroborated by significant functional improvement. 16/34 (47%) subjects who received the active treatment met the criteria for success at three months, while only 2/17 (12%) sham treated subjects did so.
Study results, as noted above, have been variable. This would be expected when the differences in selection criteria and RFL technique are taken into consideration. However, the randomized, controlled trials (RCTs) that have made use of larger volume lesions show positive treatment results that cannot be attributed to a placebo effect. What is needed are additional studies using more rigorous selection criteria and larger volume lesions that incorporate the known target lesion zone. Only then will we know the optimal treatment outcomes and rates of success from the use of RFL to treat pain related to the sacroiliac joint complex.
Applying the correct technique for the ablation of the L5 DR and sacral 1-3 lateral branches requires proper training and a precise approach. A probe that delivers the radiofrequency lesions must be able to provide a higher volume lesion to accommodate the variable and more diffuse location of the target lateral branches. Ideally, this probe would also be available at a price that is affordable. In recognition of, and as a solution for, these problems, a novel, direction-specific RF probe was designed (Nimbus Concepts, Inc.). The probe allows for a facile and time efficient technique, which may enhance the probability of adequate coagulation of the targeted L5DR and S1-3 lateral branches.
Disclosure: Dr. Bainbridge is the Research Director for Nimbus Spine, LLC, and is leading research protocol development efforts and collaborating with outside researchers who will carry out what we hope will become the definitive clinical trial for the procedure of SIJ RFN.
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