A Prospective Trial of Cooled Radiofrequency Ablation of Medial Branch Nerves Versus Facet Joint Injection of Corticosteroid for the Treatment of Lumbar Facet Syndrome

Chronic, non-neurogenic low back pain (CLBP) is a common condition that affects many individuals across their lives. The lumbar facet joint has been implicated as an important source of CLBP, with a prevalence of 15-45%. Elements of clinical history, physical examination, and imaging (radiographs, standard CT scan, standard MRI sequences) provide poor diagnostic specificity for pain of lumbar zygapophysial joint (Z-joint) origin. Thus, clinicians have traditionally relied upon MBN blocks to confirm or refute this diagnosis. The reference standard for the diagnosis of lumbar Z-joint pain is a positive response to dual comparative MBN blocks, which requires pain reduction of great than or equal to 80% of concordant duration to that expected of two different local anesthetics on independent occasions. Further, dual comparative MBN blocks have a high positive predictive value for determining the clinical outcome of lumbar MBN RFA for the treatment of lumbar Z-joint pain; when patients are appropriately selected using this reference standard and rigorous MBN RFA technique is implemented according to practice guidelines, studies demonstrate excellent clinical outcomes.

In additional to MBN RFA, lumbar facet joint injection of corticosteroid is another commonly used treatment strategy for lumbar facet joint pain related to osteoarthritis. While clinical outcome studies of facet joint injection with corticosteroid have generally shown only modest outcome improvements, this literature is generally flawed by invalid selection protocols that do not require dual comparative MBN blocks in order to confirm the diagnosis of pain specific to the lumbar facet joint(s).

Despite the widespread use of these two techniques (lumbar MBN RFA vs. facet joint corticosteroid injection), the two techniques have never been compared in an appropriately-designed head-to-head study. The sole outcome study comparing these two treatment methods used an invalid selection protocol of one positive MBN block, requiring only 50% relief in pain and not of concordant duration with that expected by the local anesthetic used; in addition, a single RFA lesion was applied with a 20g conventional RFA electrode and fluoroscopic images were not published, so it is unclear if parallel electrode technique was used, as is necessary with conventional RFA. This invalid patient selection and RFA technique protocol is similar to that used in the Mint Trials, which has led to a broad call for improving such standards in research and clinical care by a multitude of experts representing interventional pain, spine, and radiology specialty societies. As such, an appropriately designed head-to-head trial in warranted.

Furthermore, while the conventional RFA modality has been studied extensively for MBN RFA, minimal outcome literature on the effectiveness of C-RFA technology has been published. C-RFA is similar in mechanism to conventional RFA: a thermal lesion is created by applying radiofrequency energy through an electrode placed at a target structure. In C-RFA, a constant flow of ambient water is circulated through the electrode via a peristaltic pump, maintaining a lowered tissue temperature by creating a heat sink. By removing heat from tissues immediately adjacent to the electrode tip, a lower lesioning temperature is maintained, resulting in less tissue charring adjacent to the electrode, less tissue impedance and more efficient heating of target tissue. The volume of tissue heated, and the resultant thermal lesion size is substantially larger with C-RFA, conferring an advantage over conventional RFA. Further, given the spherical geometry and forward projection the C-RFA lesions beyond the distal end of the electrode, the RFA probe can be positioned at a range of possible angles and still capture the target neural structure, whereas more fastidious, parallel positioning is required with conventional RFA. These technical advantages increase the probability of successful denervation of neural pain generators that have variability in anatomic location, as is the case with facet syndromes in which significant osteoarthritis is present, which is associated with joint hypertrophy and osteophyte formation. Additionally, a longer lesion of the MBN may be more reliably achieved with C-RFA compared to conventional RFA, potentially resulted in greater treatment durability, as the recurrent of facetogenic pain after successful denervation is related to reinnervation by nerve re-growth to bridge the gap created by the lesion. Consistent with this technical advantage, there is preliminary evidence for superiority of C-RFA compared to both conventional RFA and other novel RFA techniques in the treatment of sacroiliac joint-mediated pain.

Lumbar facet joint pain is a common and costly cause of chronic low back pain. Lumbar MBN RFA and facet joint injection of steroid are two commonly used treatment strategies for lumbar facet-mediated pain, yet the two techniques have never been compared in an appropriately-designed head-to-head trial. Further there is minimal clinical outcome literature describing the effectiveness of MBN C-RFA despite its technical advantages over conventional MBN RFA. We will determine if individuals with lumbar facet syndrome who are treated with MBN C-RFA compared to face joint injection of corticosteroid have a greater likelihood of experiencing meaningful relief of low back pain symptoms, functional improvement, and reduction of analgesic medication use at both short and long-term follow-up. Answering this clinical question will help determine which standard of care technique is superior, such that patients with lumbar facet syndrome can get be offered the best treatment available.

As such, the goal of the proposed study is to determine if individuals with lumbar facet syndrome who are treated with C-RFA of the MBNs compared to face joint injection of corticosteroid have a greater likelihood of experiencing meaningful relief of low back pain symptoms, functional improvement, and reduction of analgesic medication use at both short and long-term follow-up.