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.
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.
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
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