A minimum of 50% pain relief following a prognostic genicular nerve block may not predict pain relief following genicular nerve cooled radiofrequency ablation in patients with chronic knee pain due to osteoarthritis, according to a Pain Medicine study.
To evaluate the predictive value of pain relief of a genicular nerve block, 63 patients with chronic knee pain secondary to osteoarthritis were randomly assigned to receive a prognostic genicular nerve block prior to cooled radiofrequency ablation (cRFA; n=32) or no block prior to cRFA (n=31).
In the group that received a prognostic block, only patients who had >50% pain relief for 6 hours following the block were included in the analysis for post-cRFA pain relief. The primary outcome was the rate of participants with >50% improvement in pain assessed with the Numerical Rating Scale 6 months after intervention.
Of the 32 participants who received a prognostic block, 29 patients who experienced >50% pain relief subsequently received cRFA. No significant difference in the percentage of patients reporting >50% pain relief at 6 months was reported for the prognostic block group compared with the no prognostic block group (58.6% vs 64.0%; P =.34).
In a similar manner, the rates of 15-point decreases in the scores of the Western Ontario and McMaster Universities Osteoarthritis Index were not significantly different between groups (55% vs 60%; P =.36). The percentage of patients reporting feeling “very much improved” and “improved” in the Patient Global Impression of Change was similar in both groups (31% for prognostic block vs 36% for no prognostic block; P =.65).
In an exploratory analysis of patients who reported >80% and >90% pain relief after the prognostic block, the rate of patients who met the primary outcome increased in patients who had >50% pain relief (41.7% vs 51.9% vs 60.0%). These improvements, however, were not statistically significant.
In an interview with Clinical Pain Advisor, Zachary McCormick, MD, assistant professor of spine and pain medicine at the University of Utah School of Medicine and lead study investigator, called the results “surprising.” He concluded that “it is likely that more stringent selection criteria, in accordance with the Spine Intervention Society guidelines, would result in a lower false-positive rate and improved positive predictive value for the outcome of genicular nerve cRFA.”
McCormick ZL, Reddy R, Korn M, et al. A prospective randomized trial of prognostic genicular nerve blocks to determine the predictive value for the outcome of cooled radiofrequency ablation for chronic knee pain due to osteoarthritis [published online December 28, 2017]. Pain Med. doi:10.1093/pm/pnx286