Schmidt, Peter C. MD*; Pino, Carlos A. MD†; Vorenkamp, Kevin E. MD*
From the *Department of Anesthesiology, University of Virginia, Charlottesville, Virginia; and †Department of Anesthesiology, University of Vermont, Fletcher Allen Health Care, Burlington, Vermont.
Peter C. Schmidt, MD, is currently affiliated with Department of Anesthesiology, Stanford University, Palo Alto, California.
Kevin E. Vorenkamp, MD, is currently affiliated with Department of Anesthesiology, Virginia Mason Medical Center, Seattle, Washington.
Accepted for publication March 12, 2014.
The authors declare no conflicts of interest.
Reprints will not be available from the authors.
Address correspondence to Kevin E. Vorenkamp, MD, Virginia Mason Medical Center, 1100 Ninth Ave., Mail Stop B2-AN Seattle, WA 98101. Address e-mail to email@example.com.
Pain originating from the sacroiliac (SI) joint is a common source of low back pain, with different authors estimating that SI joint etiology accounts for 15% to 30% of axial low back pain.1–3 This percentage is even higher in those who have undergone lumbar fixation4–6 and those with ankylosing spondylitis and other spondyloarthropathies.7 Other stated risk factors for the development of SI joint pain are leg length discrepancy, prolonged vigorous exercise, and gait abnormalities.8 Typically, the pain is located in the buttock region but may cause referred pain to the lower lumbar area, groin, and posterior leg.
The SI joint is a large diarthrodial joint with a true synovium located in the anterior part of the joint. Especially relevant to radiofrequency ablation (RFA) procedures, the innervation of the SI joint is variable and remains somewhat controversial, with posterior innervation often arising from the lateral branches of S1 to S3 (and occasionally S4), the L5 and potentially the L4 and even L3 dorsal rami. Some claim that the anterior aspect of the joint is entirely without innervation, while others state variable contributions from the ventral rami of L2 to S2.8
Diagnosis of SI joint pain based on history and clinical examination is difficult. Individual provocative maneuvers have weak sensitivity and specificity, but when combined, can improve the accuracy of the diagnosis.9,10 Relief of pain after a diagnostic SI joint block remains the gold standard for diagnosing SI joint pain but should be interpreted in combination with the results of multiple provocative maneuvers.11
RFA of the nerves innervating the SI joint has been proposed as part of the conservative therapy for patients experiencing pain originating from the SI joint.12–15 Different approaches and techniques have been described with variable but overall positive results. In the past few years, a probe (Simplicity III, NeuroTherm®, Wilmington, MA) was introduced to ablate the lateral branches that innervate the SI joint with a single percutaneous entry point. The Simplicity probe is a solid radiofrequency electrode with 3 active areas that create 3 monopolar lesions and 2 bipolar lesions in a sequential manner across the lateral branches of S1 to S4 (Fig. 1). According to the manufacturer’s information, the lesion size created is 9 × 52.5 mm.16,17 Claimed advantages of this probe include a single percutaneous insertion site, no need for cannulae or introducers and the creation of a continuous “strip” lesion that ensures capture of most lateral branches. The only clinical data on the Simplicity probe were presented in an abstract detailing the results of the first 19 procedures performed.a
This was a noncontrolled retrospective review of cases of RFA of the SI joint performed at 2 academic institutions. All procedures were performed by 2 of the authors (KV, CP) since May 2009 at Institution 1 and October 2008 at Institution 2 and were the result of a change in practice. Before this, all SI joint RFAs were performed using the “leap-frog” technique with bipolar lesions or individual thermal lesions of the sacral lateral branches, whereas after this change in practice we began using the Simplicity probe for many patients. All patients who had SI joint RFA were included in the analysis with the exception of 5 patients who were lost to follow-up. Our respective IRBs determined that approval was not required as part of a reportable quality improvement project.
All patients who had clinical suspicion of SI joint pain (ICD-9 724.6) underwent fluoroscopically guided diagnostic intra-articular injections with bupivacaine and steroids. Those with >50% pain relief from diagnostic injections were offered RFA on a subsequent visit.
As with traditional RFA techniques, the patient is placed in the prone position and landmarks are identified via fluoroscopy. Placement of the probe is accomplished by identifying the bony margin lateral to the S4 foramen. The overlying skin and the intended probe trajectory area on the sacral plate are anesthetized with local anesthetics. A 25-gauge 3.5-inch Quincke needle was used to anesthetize deeper tissues as needed for patient comfort. Under fluoroscopic guidance, the probe is inserted through the skin to contact the bony margin lateral to the S4 foramen and then advanced to lie over the posterior sacral plate (Figs. 2 and 3). Depending on the final positioning, 2 or 3 active areas can be selected to create 3 or 5 lesions, respectively. We followed the Neurotherm protocol, wherein each lesion is created at 80°C or 85°C for 60 to 90 seconds.17 Patients who were not fused at L5-S1 also had RFA lesions (80°C, 90 seconds) performed of the L5 dorsal ramus. A small proportion of patients at Institution 2 also had lesions performed at the L4 medial branch nerve.
Seventy-seven RFA treatments were performed on 60 patients with the Simplicity probe. A clinician called each patient at 6 weeks, 6 months, and 1 year after the procedure. Patients were asked to rate their pain level using a Verbal Pain Scale (0–10), and procedures resulting in >50% pain relief were considered a successful outcome.
Of the 77 radiofrequency treatments, 71.4% (N = 55) were considered a successful outcome at 6 weeks, defined as having >50% pain relief (Table 1). At 6 months, 54.5% (95% confidence interval [CI], 42.8%–65.8%) of the treatments continued to have a successful outcome and this continued in 15.6% (N = 12) at 1 year.
Our results compare favorably with other techniques of SI joint RFA. More than half of our patients (54.5%) had significant (>50%) clinical relief for at least 6 months compared with 36.4% of patients in the original study by Ferrante et al.12 with the leap-frog technique. With this technique, a series of radiofrequency cannulae are inserted along the inferior SI joint and several bipolar lesions are then performed along the posterior border of the joint, typically at 80°C for 60 to 90 seconds.18,19
A meta-analysis of 5 studies with 6 total groups found a success rate of 42.3% to 57.6% at 6 months, with a pooled mean of 49.9%.20 These results are similar to our initial results (54.5%, 95% CI, 42.8%–65.8%). There was no subanalysis of outcomes at 1 year in this meta-analysis with which to compare, although Cohen et al.21 found that 14% of patients had persistent pain relief at 1 year. In summary, our initial results using the Simplicity probe are within the range of those reported for the leap-frog technique and with cooled RFA.
We found that 16 of 77 radiofrequency lesions failed, in that they provided no clinically significant relief to the patient. Cohen et al.21 identified a number of potential predictors of outcome failure, including higher preprocedure pain scores, longer duration of symptoms, and frequent opioid use. None of these variables was documented consistently enough to analyze in our study. Another interesting consideration is that the failure rate could be secondary to variable contributions of anterior innervation.22,23
In contrast to other SI joint radiofrequency techniques, the main advantages of this probe are the single insertion site, the potential of neurolysing most of the lateral branch nerves with a single continuous lesion, and possibly faster performance. A potential disadvantage may be that the lesion size of the single insertion, single depth probe may be inadequate to account for the different depths at which the nerves supposedly travel as described by Dreyfuss et al.24,25 Finally, in patients with larger body habitus, it may be more challenging to align the probe directly over the sacral plate.
This case series suffers from several limitations beyond those inherent in a noncontrolled study. First, there was slight variation in treatment regimens between institutions, with a small number of patients at 1 institution receiving L4 medial branch lesions. This group was of insufficient size to analyze as a subgroup. Furthermore, we recognize that these data would be more robust with the addition of patient functional assessments and thorough patient demographic information, as well as a comparison to historical controls. Unfortunately, this information was not consistently available for our interpretation.
The results of this case series suggest that the Simplicity probe is a promising tool for providing intermediate-term relief of SI joint pain. Our results are comparable to those found with the original leap-frog technique and within the range of the relief provided by cooled radiofrequency at 6 months. Our data further support that SI joint RFA is an effective treatment in selected individuals with chronic pain originating at the SI joint.20,26,27
We believe that the next step in evaluating this new technology is an appropriately powered randomized controlled trial in which the Simplicity probe is compared to traditional RFA techniques to determine comparative pain relief at various intervals, as well as any differences in functional capacity and quality of life.
Name: Peter C. Schmidt, MD.
Contribution: This author helped analyze the data and write the manuscript.
Attestation: Peter C. Schmidt approved the final manuscript.
Name: Carlos A. Pino, MD.
Contribution: This author helped design and conduct the study, analyze the data, and write the manuscript.
Attestation: Carlos A. Pino approved the final manuscript.
Name: Kevin E. Vorenkamp, MD.
Contribution: This author helped design and conduct the study, analyze the data, write the manuscript, and clinical care of patients.
Attestation: Kevin E. Vorenkamp approved the final manuscript.
This manuscript was handled by: Spencer S. Liu, MD.
a B Starr, Dahle N and KE Vorenkamp. Radiofrequency Lesioning of the SI Joint with the Simplicity III Probe: A case series. Reg Anesth Pain Med 2009; MCC:28 Cited Here...
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