ASRA Pain Medicine News, May 2024

Evidence for Diagnostic Blocks Prior to Radiofrequency Ablation of Innervation to the Lumbar Facet Joints—None, Once, or Twice?

May 2, 2024, 06:07 AM by Sireedhorn Assavanop, MD, and Anuj Bhatia, MD, PhD, FRCPC

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.


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.


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 pathology3-5 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


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 sources7-9, 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.

Table 1: Studies evaluating diagnostic block(s) and facet joint radiofrequency ablation.



Number of subjects

Number of diagnostic blocks

Determining positive diagnostic blocks
(% pain relief and time of assessment)

Comparator groups

Determining successful outcomes for radiofrequency ablation (RFA)

Time point of assessment after RFA

• Results
• Adverse effects

Cohen et al

Randomized multicenter study

Objectives: identifying treatment paradigm associated with the lowest cost per successful outcome


0-2 (randomized 1:1:1)

  • ≥50% pain relief
  • Lasting ≥3 h for bupivacaine
  • Lasting ≥1 h for lidocaine

Group 0: proceed directly to RFA without diagnostic block

Group 1: proceed to RFA if obtained a single positive diagnostic block

Group 2: proceed to RFA only if obtained concordant pain relief after comparative blocks

≥50% pain relief with a positive global perceived effect persisting for ≥3 months

At 1 and 3 months

  • Successful outcomes at 3 months; n (%)
    • gr0: 17/51 (33)
    • gr1: 8/49 (16)
    • gr2: 11/49 (22)
  • Denervation success rates; n (%)
    • gr0: 17/51 (33)
    • gr1: 7/18 (39)
    • gr2: 9/14 (64)
  • Cost per successful treatment; USD
    • gr0: $6,286
    • gr1: $17,142
    • gr2: $15,241
  • Worsening back pain after RFA: 2 patients (resolved at 3 months)
  • New radiating leg pain: 1 patient (resolved at 3 months)

McCormick et al

Prospective outcome study

Objectives: investigate function, pain, and medication use outcomes of RFA for lumbar facet syndrome with long-term FU



  • If after a single block:
    1. >75% pain relief -> RFA
    2. >50 but ≤75% -> second block
  • Concordant duration with LA used.


  • ≥50% improvement in function
  • ≥50% pain reduction; change in median NRS, daily morphine equivalent consumption, Medication Quantification Scale III (MQS III) score

• Median duration of follow-up = 39 months

  • Function and pain improved by ≥50% in 58% (CI 45%, 71%) and 53% (CI 40%, 66%), respectively.
  • Median reduction in MQS III score = 3.4 points, demonstrating durable effect of RFA at long-term FU.
  • Individuals who underwent two sets of diagnostic blocks were 17% and 16% more likely to experience improvement in function and pain, respectively (not statistically significant).
  • No complications occurred.

Provenzano et al

Single-center retrospective review


  1. Understanding influence of second block on progression to lumbar RFA under pain relief thresholds of either 50% or 80%.
  2. Evaluating potential impact of Medicare Administrative Contractors Requirement$on utilization and associated economic consequences of a second block.



≥50% pain relief on first block -> then second diagnostic block

• first block categories of 50%–79% pain relief vs. 80% pain relief



  • Most achieved the same or better pain relief block category with the second block.
  • Individuals with ≥80% relief on first block are 87% more likely to achieve that same threshold on second block relative to an individual with 50%–79% relief on first block.
  • Two diagnostic blocks with ≥80% pain relief result in 43.8% (95% CI 36.8 to 50.9) RFA procedure volume reduction, when compared with 50% pain relief threshold.
  • One-block paradigm resulted in >15% cost reduction.

Bhandari et al

Prospective randomized open-label comparative study


  1. Assessing outcome of RFA after single and dual MBB
  2. Determining PPV of diagnostic single and dual MBB for RFA in LBP



Group S: ≥ 80% pain relief ≥ 2h -> RFA

Group D: ≥ 80% pain relief ≥ 2h for lidocaine, and second block with bupivacaine requires ≥80% pain relief ≥3h (2 weeks apart) -> RFA

Group S (n = 15): single MBB with 1% lidocaine 0.3 ml

Group D (n = 15): dual MBB with 1% lidocaine 0.3 ml, and if positive -> proceed to second block with 0.25% bupivacaine 0.3 ml

≥3 points reduction in NRS compared to preprocedure

At 1 month

  • Significant difference between NRS preprocedure and 1 month post-RFA in both groups (Group S, Pre 8.66±0.89, Post 4.26±1.53, p 0.001; Group D, Pre 8.13±1.87, Post 3.20±1.20, p 0.001)
  • NRS in Group D was lower than Group S at1 month after RFA (P = 0.034).
  • PPV: Group S, 66.6%; Group D, 86.6% at 1 month post‑RFA.
  • No complications observed.

Cohen, et al

Multicenter, prospective correlational study

Objectives: Determining optimal pain relief threshold for selecting patients for RFA after diagnostic MBB



≥ 50% pain relief

< 50% pain relief after diagnostic blocks but satisfied with the results

≥ 50% reduction in NRS for >3 months with positive global perceived effect, irrespective of functional benefit

At 1 and 3 months

  • ROC curve revealed ≥ 43% to provide greatest separation for selecting RF candidates (not statistically significant); AUC 0.57 (95% CI: 0.42, 0.72); 100% sensitive, 18% specific, with observed agreement (ie, success rate) of 59%.
  • No significant differences in RF outcomes on any MBB pain relief cutoff over 50%.
  • Patients obtained <50% pain relief reported poorer outcomes (17% success rate vs. 58.2% success rate; P=0.19).
MBB = medial branch block, RFA = radiofrequency ablation, h = hours, LA = local anesthetics, NRS = numerical rating scale, FU = follow-up, PPV = positive predictive value, LBP = low back pain, Medicare administrative contractors requirement$ = the requirements of two preceding diagnostic blocks with ≥80% pain relief before RFA, ROC = receiver’s operating characteristic curve of success versus post procedure relief at 1 month, AUC = area under the curve.
Sireedhorn Assavanop
Sireedhorn Assavanop, MD, is with the department of anesthesia and pain medicine at the Toronto Western Hospital and the University of Toronto in Toronto, Ontario, Canada.
Anuj Bhatia
Anuj Bhatia, MD, PhD, FRCPC, is with the department of anesthesia and pain medicine at the Toronto Western Hospital and the University of Toronto in Toronto, Ontario, Canada.


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