“We simply lack a good strategy for efficiently selecting those who will receive benefit from radiofrequency ablation [for low back pain].”
Low back pain is one of the most common causes of chronic pain, disability, lost productivity, and cost, affecting more than 66 million Americans in 2012.1–3 A large number of treatments are available, including behavioral therapies, chiropractic care, exercise, injections, massage, medications, surgery, and others, with no empirically validated approach to selecting the best treatment for any individual patient. Nevertheless, consensus guidelines for low-back pain management generally emphasize conservative strategies over interventional approaches because they are perceived to be of lower cost and less risk.4,5 In contrast to the recommendations of these guidelines, needle-based interventions are very commonly used for low-back pain treatment. In fact, interventions of the facet (zygapophyseal) joints are the second most common procedure in interventional pain medicine.6 Whereas benefits of radiofrequency ablation under idealized circumstances have been established through multiple clinical trials,6 the general real-world results have been a source of recent controversy after the publication of the Mint trial.7 The Mint trial combined three separate pragmatic, nonblinded randomized trials of low back pain, sacroiliac joint pain, and a combination of the two and found that radiofrequency ablation combined with a standardized exercise program was no better than the standard exercise program alone. The study has been critiqued by experts for issues with patient selection, diagnostic blocks, and radiofrequency ablation technique. These results, in the context of rapidly increasing medical cost consciousness, place pressure on interventionalists to identify those patients most likely to benefit from their procedures.
In this edition of Anesthesiology, Cohen et al.8 present the results of a two-stage, randomized, controlled trial of 229 chronic axial low-back pain patients from multiple military and Veterans Affairs hospitals, one academic center, and one private hospital. In the first stage, low-back pain patients were randomized to receive medial branch blocks, intraarticular steroid facet blocks, or a saline control. The trial assessed the initial response to injection and pain severity one month later (first coprimary outcome). In the second stage, those who had positive initial responses to medial branch or intraarticular blocks and all patients who had saline injections proceeded to radiofrequency ablation. Pain severity 3-months postablation was then assessed (second coprimary outcome). The authors’ a priori hypotheses were (1) that intraarticular blocks with local anesthetic plus steroid would provide greater 1-month improvement in pain than medial branch blocks with local anesthetic plus steroid or saline injections, and (2) that patients having radiofrequency ablation would have lower 3-month pain scores if they had a positive response to medial branch blocks than if they had a positive response to intraarticular blocks or if they had only a saline injection before radiofrequency ablation.
No Improvement in Pain 1 Month after Intraarticular or Medial Branch Blocks with Steroid
Although there are many pain physicians who use intra-articular blocks as a treatment modality for low back pain, the data supporting single blocks as a therapeutic procedure have been mixed at best.6 Counter to the authors’ hypothesis, but perhaps not their expectations, the study found that neither intraarticular or medial branch blocks with steroid reduced low back pain to an extent greater than saline injection, even with the 4-week short-term outcome. There were also no differences in the secondary outcomes, including physical function, satisfaction, or reduction in medication use. These clinically important results are not particularly surprising, as pain from the zygapophyseal joint is not typically inflammatory or acute in nature and therefore not likely to respond to steroid. This study further refutes this practice. Also relevant is the more technically challenging nature of intraarticular blocks and the finite likelihood of unintentional epidural injection via synovial-epidural communication and infection. Moreover, given that pain patients may be receiving steroids to treat their low back pain, other pain, or medical conditions, caution needs to be used with additional steroid injection in general.
No Difference in 3-month Postradiofrequency Ablation Outcomes between Groups
In the radiofrequency ablation second stage of the trial, only those experiencing 50% or more response to the diagnostic block in the intraarticular block and medial branch blocks groups proceeded to radiofrequency ablation (51% and 53%, respectively), whereas all participants in the saline control group were offered radiofrequency ablation, and 91% proceeded with the intervention. At the 3-month postradiofrequency ablation primary outcome time point, there was no difference in the coprimary pain outcome, with all groups experiencing similar pain relief. Moreover, there were no differences in secondary outcomes of physical function, satisfaction, or reduction in medication use between the three groups. This should not be misinterpreted as a lack of efficacy for radiofrequency ablation, as all participants in these analyses had radiofrequency ablation. While somewhat disappointing, these data build on a previous study by Cohen et al. that suggested that radiofrequency ablation without diagnostic blocks may be the most cost-effective approach when compared to only performing radiofrequency ablation for those responding to one or two diagnostic medial branch blocks, as is often required by insurers.9 Not only do these studies8,9 suggest that proceeding directly to radiofrequency ablation may be the most cost-effective pathway, but this approach would avoid excluding patients that may benefit due to false-negative diagnostic blocks.6 In one of the author’s (J.D.C.) Veterans Affairs institutions, diagnostic blocks before radiofrequency ablation were abandoned more than a decade in the past as inefficient. In contrast, some insurance companies mandate two diagnostic blocks before radiofrequency ablation.
There were secondary outcomes related to the block group assignment that merit discussion. Participants in the intraarticular and medial branch blocks groups were more likely to report a positive immediate response after the block than the saline control group (54% vs. 55% vs. 30% for intraarticular, medial branch, and saline groups, respectively), suggesting that the active injections may in fact have some degree of diagnostic utility. Furthermore, the strongest predictor of a positive outcome after radiofrequency ablation was a positive response to the diagnostic block (adjusted odds ratio 6.87; 95% CI, 2.04 to 23.13). While group-wise pain reductions were similar after radiofrequency ablation, the proportion of patients experiencing meaningful pain reduction was larger in the medial branch blocks and intraarticular diagnostic block positive groups. While large in absolute terms, it is unclear what the odds ratio would need to be in order to justify the use of diagnostic injections.
Clinical Implications and Future Directions
The study by Cohen et al.8 clearly demonstrates the lack of therapeutic benefit from intraarticular and medial branch blocks; however, applying radiofrequency ablation findings is more challenging. Participants in all radiofrequency ablation groups derived clinically significant reductions in pain at the 3-month time point. There have been many studies in the last decade to better understand the patient characteristics, diagnostic block response, and procedural techniques associated with the best outcomes after radiofrequency ablation. All studies are currently severely limited by the lack of a definitive standard for diagnosing pain from the facet joint and for differentiating facet pain from the many other potential pain generators associated with low back pain. We simply lack a good strategy for efficiently selecting those who will receive benefit from radiofrequency ablation. On the other hand, most of the alternative treatments also have significant limitations. The use of opioids for low back pain is fraught with peril and was further refuted in a recent 12-month randomized, controlled trial.10,11 While spine surgery plays an important role in well-selected patients, surgery can lead to worsened pain, major complications, and new chronic opioid use.12,13 Conservative measures, although safe, typically provide modest relief, often of limited duration. Interventional pain management, including medial branch radiofrequency ablation, remains an important treatment modality, although we continue to struggle to establish its position in the treatment algorithm for low back pain. The lack of comparative diagnostic blocks may have contributed to the negative results of the Mint trials and were among the criticisms of the study.7 Until there are more studies in which all patients undergo radiofrequency ablation to allow an unbiased assessment of the independent predictive value of patient characteristics and diagnostic block(s), we are left to question the value of diagnostic blocks as screening tools for radiofrequency ablation. The results of this study suggest that serious consideration should be given to abandoning the diagnostic block.
The authors are not supported by, nor maintain any financial interest in, commercial activity that may be associated with the topic of this article.