Cite as: Assavanop S, Bhatia A. Evidence for diagnostic blocks prior to radiofrequency ablation of innervation to the lumbar facet joints – none, once, or twice?. ASRA Pain Medicine News 2024;49. https://doi.org/10.52211/asra050124.004.

Background

Low back pain (LBP) is a common condition that results in significant burdens and costs for patients and society. Pathology of lumbar facet joint accounts for 15%-45% of LBP cases in the United States.¹ A patient's medical history, physical examination and imaging can indicate but cannot confirm facet joints as the pain generator. An analgesic response to a facet joint innervation block, usually referred to as a medial branch block (MBB), with a local anesthetic (LA) is accepted as a confirmation of the source of pain, and as a prognosticator for the outcome of interventions such as radiofrequency ablation (RFA) to alleviate pain.

Despite the ubiquitous use of diagnostic/prognostic MBBs, several controversies about its role persist. There are different opinions on what constitutes a positive diagnostic block. The issues include the number of blocks that need to be performed, the level of pain relief that is considered significant, the injectate used, and the timing for evaluating the outcome of the diagnostic blocks. The aspects debated focused on the balance between diagnostic accuracy and cost-effectiveness. To gain a better understanding of current practices in using diagnostic MBBs to prognosticate response to facet innervation RFA procedures, we performed a comprehensive literature review of PubMed, Scopus, and Google Scholar databases from inception until December 31, 2023. The search terms used include “radiofrequency,” “ablation,” “denervation,” “facet joints,” diagnostic,” “prognostic,” and “nerve blocks.” We used appropriate Boolean operators (eg, and, or) with the search terms to ensure a focused and productive literature search. Our objectives were to evaluate criteria used in clinical trials and practice for diagnostic MBBs, such as the number of block(s) mandated, the minimum level of pain relief required in response to the blocks, and the time frame for evaluating the outcome of diagnostic blocks and RFA.

Results

We found five publications that were relevant to our topic of interest (Table 1). The following is a brief overview of the conclusions drawn from the relevant articles.

Evidence in Favor of None or Only One Diagnostic MBB

Two sets of diagnostic MBBs are recommended by the International Pain and Spine Intervention Society² and many others as the most reliable method for identifying facet joint pathology^3-5 with most healthcare insurers in the United States insisting on this paradigm. According to Bogduk et al, the expenses associated with diagnostic MBBs and RFA vary among providers and countries. However, not performing the second comparative block could result in a high number of false positives because around 690 denervation failures would result that could have been prevented with a second block. Therefore, avoiding the second comparative block may not be cost-effective but could be considered unethical and inefficient.⁶ In 2010, Cohen et al. conducted a randomized, comparative cost-effectiveness study in 151 patients that compared 0, 1, and 2 diagnostic MBBs prior to RFA. In this study, it was mandated that participants who received two diagnostic blocks (one with a long- and another with a short-acting local anesthetic) must experience at least 50% pain relief with a concordant effect to proceed with RFA. Successful outcomes were determined by at least 50% pain relief coupled with a positive global perceived effect that persisted for at least 3 months. The study suggested that proceeding to radiofrequency denervation without a diagnostic block was the most cost-effective treatment paradigm (group 0: 33% successful outcome at $6,286 USD per successful outcome; group 1: 16% at $17,142 USD; and group 2: 22% at $15,241 USD).⁷ The authors proposed that the question of interest was not whether one or two diagnostic blocks should be performed prior to RFA but whether these blocks should be performed at all.

There is currently a lack of consensus on what defines a positive prognostic MBB for proceeding to RFA.

Some of the published clinical trials have included only one set of diagnostic blocks prior to proceeding with RFA. McCormick et al. evaluated outcomes of function, pain, and medication use with RFA for lumbar facet syndrome in a prospective study on 62 patients published in 2015 that employed a tiered approach. They primarily used a single set of positive diagnostic blocks for pain relief of >75% as the criterion for proceeding to RFA. Only patients with >50% but <75% relief underwent a second set of confirmatory blocks. The reasons provided for this tiered approach were lower costs, decreased risk of complications, an acceptable false-positive rate, and accelerated care. In a sub-analysis, it was discovered that individuals who underwent two sets of diagnostic MBBs, rather than just one, were more likely to have improved function and reduced pain but only by 17% and 16%, respectively; however, these results were not statistically significant.⁸

In a more recent retrospective study by Provenzano et al. using data from 224 patients, the authors echoed the tiered approach used by McCormick et al. and suggested a second diagnostic block could be beneficial only if it leads to significant changes in patient selection for RFA facet denervation procedures. They found that patients with 80% or more pain relief following the first diagnostic MBB were 87% more likely to achieve the same result with the second diagnostic MBB versus an individual with 50%–79% relief with the first diagnostic MBB. In other words, a high magnitude of pain relief with the first diagnostic MBB negates the value of a second diagnostic MBB. Further, the potential benefits of a second diagnostic MBB must be weighed against additional costs and more burden on patients with an increase in false negative responders. The study also revealed that using a single-block paradigm could reduce healthcare costs by more than 15%. In addition, requiring two diagnostic blocks with ≥80% pain relief would lead to a reduction of approximately 40% (95% CI 36.8 to 50.9) in RFA procedure volume, which may lead some individuals to refrain from undergoing a potentially beneficial procedure with sustained analgesic benefits.⁹

Evidence in Favor of Two Diagnostic MBBs

Bhandari et al. conducted a prospective comparative study on 30 patients to evaluate the effectiveness of RFA following a single or dual MBB. The authors used a cut-off criterion for MBB of at least 80% reduction in pain and concordant duration with the local anesthetic used. They observed significant pain reduction in both groups after RFA, but the magnitude of reduction was higher in the dual group (pain scores 3.20±1.20 vs. 4.26±1.53 on a 0-10 scale, p = 0.034). Additionally, they concluded that a single MBB may yield more false positive results and had a lower positive predictive value compared to dual MBB for pain relief at one month after RFA (66.6% vs. 86.6%).¹⁰

Cohen et al. conducted another prospective study in 2013 to determine the optimal pain relief threshold following a single set of MBBs for selecting patients for RFA. They found that there were no significant differences in an RFA outcome of 50% pain relief for at least 3 months coupled with a positive global perceived effect based on any pain relief cut-off above 50% after MBB. However, patients who obtained less than 50% pain relief reported proportionately poorer outcomes with a success rate of 17% compared to 58.2% for those who achieved more than 50% pain relief.¹¹

Discussion

There is currently a lack of consensus on what defines a positive prognostic MBB for proceeding to RFA. Factors that impact this include the number of blocks that need to be performed, the cut-off level for pain relief, the type of injectate and volume used, and the timing for evaluating the outcome of the RFA. In recent years, guidelines have also been published to help clarify these issues.¹² This brief review summarizes the current knowledge on this topic.

Based on the review and evidence gathered from multiple sources^7-9, it appears that a single set of MBB with concordant pain relief of at least 50% is a reasonable approach for identifying candidates for RFA of lumbar facet joints. This approach encompasses cost-effectiveness, an acceptable false-positive rate, and practicality. However, when the primary concern is the success rate of RFA such as in the setting of a scientific trial, dual sets of MBBs may be a preferred option.^{10, 12-14}

However, all the data on this topic is from patients having lumbar facet RFA, and it may not be applicable to other axial RFA procedures, such as cervical facets and sacroiliac joints. More research is warranted on this important topic. A comparative effectiveness trial approach and reliance on real world data from well-managed registries are needed to provide further insights into the best prognostic approach for RFA.

References

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2. Bogduk N. International Spinal Injection Society guidelines for the performance of spinal injection procedures. Part 1: Zygapophysial joint blocks. Clin J Pain 1997;13(4):285-302. https://doi.org/10.1097/00002508-199712000-00003
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7. Cohen SP, Williams KA, Kurihara C, et al. Multicenter, randomized, comparative cost-effectiveness study comparing 0, 1, and 2 diagnostic medial branch (facet joint nerve) block treatment paradigms before lumbar facet radiofrequency denervation. Anesthesiology 2010;113(2):395-405. https://doi.org/10.1097/ALN.0b013e3181e33ae5
8. McCormick ZL, Marshall B, Walker J, et al. Long-term function, pain and medication use outcomes of radiofrequency ablation for lumbar facet syndrome. Int J Anesth Anesth 2015;2(2). https://doi.org/10.23937/2377-4630/2/2/1028
9. Provenzano DA, Leech JE, Kilgore JS, et al. Evaluation of lumbar medial branch blocks: how does the second block influence progression to radiofrequency ablation? Reg Anesth Pain Med 2022;47(12):719-21. https://doi.org/10.1136/rapm-2022-103754
10. Goswami S, Bhandari B, Ray S. Comparative study of positive predictive value of diagnostic single versus dual median branch block for radiofrequency neurotomy in lumbar facet joint syndrome. Indian Journal of Pain 2021;35(2).
11. Cohen SP, Strassels SA, Kurihara C, et al. Establishing an optimal “cutoff’ threshold for diagnostic lumbar facet blocks: a prospective correlational study. Clin J Pain 2013;29(5):382-91. https://doi.org/10.1097/AJP.0b013e31825f53bf
12. Cohen SP, Bhaskar A, Bhatia A, et al. Consensus practice guidelines on interventions for lumbar facet joint pain from a multispecialty, international working group. Reg Anesth Pain Med 2020;45(6):424-67. https://doi.org/10.1136/rapm-2019-101243
13. Falco FJ, Manchikanti L, Datta S, et al. An update of the systematic assessment of the diagnostic accuracy of lumbar facet joint nerve blocks. Pain Physician 2012;15(6):E869-907.
14. Bogduk N. Practice Guidelines for Spinal Diagnostic and Treatment Procedures. Hinsdale, Illinois: International Spine Intervention Society; 2013.