The factors predicting outcome of RF facet denervation were assessed in a retrospective chart review. Patients with paraspinal tenderness were more likely to have significant pain reduction 6 months after the intervention. Response to facet loading, long duration of pain, and previous back surgery were factors associated with treatment failure [29
]. A recently published prospective observational study found depression, previous surgery, and number of treated joints to be predictive for a shorter duration of effect of RF facet denervation [28
Whereas a diagnostic block is recommended to confirm the facet joint involvement, there is no consensus on the choice between intra-articular and ramus medialis injection, number of blocks to be performed, and cut-off value for judging the block to be positive. A comparison of the treatment outcome in patients reporting 50%–79% pain relief and those experiencing more than 80% pain relief for the duration of action of the local anesthetic showed no significant difference [30
The accuracy of facet blocks also depends on the way the diagnostic block is performed [31
•]. In the seven controlled studies on the efficacy of RF facet denervation there is one negative study [9
] and one equivocal study [10
]. In both of these studies, intra-articular injection of local anesthetic was used as diagnostic block instead of the block of the ramus medialis of the ramus dorsalis, the application of the local anesthetic on the nerve innervating the facet joint. Moreover, the interpretation of the diagnostic block used in the negative study is highly controversial as outlined above. Based on the evaluation of these studies, intra-articular injection of local anesthetic no longer can be recommended as a diagnostic for prediction of response to RF treatment.
Facet blocks, as with all diagnostic spinal injections, lack accuracy [32
]. Reports of false-positive rates range between 20% and 40% [33
]. These findings, and the observation that in studies where patients were selected by means of comparative blocks the number needed to treat is the lowest, led to the proposal for use of controlled or confirmative blocks [36
However, there is controversy over the added value of multiplying the examinations before offering definite treatment to chronic pain patients. A well-conducted RCT investigated costs and outcomes of RF treatment using three different medial branch blocks treatment paradigms: 1) RF denervation without the use of a screening block; 2) RF denervation if the patient obtains significant relief after a single diagnostic block; and 3) RF denervation only if an appropriate patient has a positive response to two confirmatory blocks [39
••]. By 3 months after RF treatment, the proportion of successful outcomes for each individual group cohort was highest in the group where patients received RF treatment without prior block (33%) compared to 16% in the group of patients who had one diagnostic block and 22% in the group of patients who had comparative blocks. Based on the reimbursement scales applicable in the United States at the time of the study, the most cost-effective treatment was performed without prior diagnostic block. However, the success rates were reversed from the overall success rates when only those patients who received RF treatment were evaluated. In the group without diagnostic block, 33% of the patients had a successful outcome. This was 39% in the group with a single block and 64% in the double-block group. These findings confirm earlier observations that treatment outcome is better when the patients have been carefully selected [40
However, this does not mean that controlled blocks can be recommended as standard procedure. Indeed, with each additional diagnostic block, the number of false-positive blocks is reduced, but the number of false-negative blocks increases, which means that the risk of withholding efficacious treatment from patients is also increased.
Besides the balance of the burden of multiple interventions related to extra visits and interventions associated with controlled diagnostic blocks, the potential benefit also should be considered. In the mentioned controlled study [39
•], a 25% increase in successful outcome is obtained with two diagnostic blocks, but this requires 100% more diagnostic interventions. Does the small gain in success justify the extra burden for the patient, the higher costs, and possible side effects of an additional treatment session? Moreover, only minor and transient side effects are reported in the literature after RF facet denervation [26
The main objective of performing a diagnostic block is confirming the involvement of the facet joint and the level as diagnosed by clinical examination. However, there is a need for standardization. Based on the information from the literature, we suggest these measures:
- One block of the ramus medialis of the ramus dorsalis, no intra-articular injection;
- Three injection needles, placed at three adjacent levels under fluoroscopic control;
- A limited amount (maximum 0.7 mL) of local anesthetic without corticosteroids per level;
- Evaluation of the change in pain intensity and functionality during the duration of action of the local anesthetic; and
- A VAS or numeric rating scale for assessment of the pain intensity, with a nurse assisting the patient in this assessment.