Effectiveness of Genicular Nerve Cooled Radiofrequency Ablation on Chronic Knee Osteoarthritis Pain

Abstract

Background: Outside of an invasive total knee arthroplasty, the available therapies for the treatment of pain secondary to knee osteoarthritis (OA) provide marginal and short-lived symptomatic relief. Genicular nerve radiofrequency ablation (RFA) serves as an alternative treatment modality for OA-associated knee pain and disability. Objectives: To quantify the effectiveness of cooled radiofrequency ablation (C-RFA) of the genicular nerves for chronic knee pain secondary to OA. Study Design: Retrospective chart review performed using Redcap, implementing current procedural terminology codes. Setting: An academic pain management center. Methods: Study population included patients treated with C-RFA from April 2015 through June 2017. Numeric Rating Scale (NRS) data were analyzed at 3 time points: 2 weeks, 4-6 weeks, and 7-33 weeks post-RFA (extended follow-up). Primary outcome for statistical analysis was NRS and the change in NRS from baseline at each of the 3 predetermined time points. Differences between the change in NRS and the number of diagnostic blocks performed (1 vs. 2) was evaluated. Correlation between the change in NRS and patient body mass index (BMI) was calculated. Results: Pre-RFA average NRS scores were available for 47 knees from 31 individuals, which were included in the analysis. The mean NRS score decreased by 50% at 2 weeks (n = 33; P < 0.001), 55% at 4-6 weeks (n = 18; P < 0.001), and 26% at 7-33 weeks (n = 18; P = 0.009). Eight patients (12 knees) provided specific data on the total duration of relief following RFA. The mean duration was 39 weeks or approximately 9 months. There were no statistically significant differences between groups receiving 1 versus 2 diagnostic blocks at 2 weeks or 4-6 weeks post- RFA. At 7-33 weeks, those who received 1 block had a decrease in NRS of –3.1, whereas those who received 2 blocks had an increase in NRS of +0.1 (P = 0.008). There was no correlation identified between BMI and change in NRS at any time point. Limitations: This study’s retrospective design inherently leads to a higher risk of selection bias. The sample size was relatively small as a high percentage of patients were lost to follow-up. The primary outcome measure for this study was the change in mean NRS pain score, and the mean of ordinal data with a nonnormal distribution lacks validity in statistical analysis. Conclusions: In this study population, C-RFA of the genicular nerves lead to 50% or greater pain relief at 2 weeks and 4-6 weeks postintervention. A 26% pain relief was achieved at 7-33 weeks, but this did not meet the established minimal clinically important difference cutoff. Two diagnostic genicular nerve blocks did not improve the rate of treatment success when compared to a single diagnostic block. BMI does not appear to correlate with outcomes. Key words: Genicular radiofrequency ablation, genicular RFA, cooled radiofrequency ablation, chronic knee pain, knee osteoarthritis