Comparisons of Lesion Volumes and Shapes
Produced by a Radiofrequency System with a
Cooled, a Protruding, or a Monopolar Probe
Background: Radiofrequency (RF) ablation for denervation has been utilized for decades in chronic pain management. This relies on the proper targeting of the affected nerve which may be obtained by creating an ablation lesion with a shape and volume that optimizes targeting. Various systems designed to improve lesion size are available. These include cooling the active tip (cooled-RF) and protruding the RF electrode outside the active tip (PERF). Objectives: This study compares lesion volumes of 3 commercially available RF systems: cooled-RF, “V” shaped active cannula and protruding electrode (18 g and 20 g), and monopolar RF (MRF; 16 g, 18 g, and 20 g). Study Design: Ex vivo study using clinically relevant conditions. Setting: Biophysical laboratory in an academic institution. Methods: RF ablation lesions were generated in additive-free chicken breast specimens (n = 10) with the RF probes fully inserted in them. For cooled RF, a 17 g probe (4 mm active tip) was used. RF was applied for 150 seconds at 60°C. PERF was applied using 18 g or 20 g introducers (10 mm active tip) for either 90 or 150 seconds at 80°C. For MRF ablation, introducers diameter were 16 g, 18 g, or 20 g (10 mm active tip), while RF was applied for 90 seconds at 80°C. Tissues were dissected through the midpoint of the lesion, and measurements of the longitudinal, transversal, and depth lengths were taken and used to calculate the lesion volume. Measurements from the distal edge in the transverse and longitudinal directions were also recorded. One-way ANOVA was used to determine statistical significance between volume means (P < 0.05). Results: Mean lesion volume with cooled RF (595 mm3 ) is significantly larger than any other mean volume measured. The second largest volume is produced with MRF using a 16 g introducer (360 mm3 ), which is significantly larger than those obtained with 18 g or 20 g. This is also significantly larger than the one obtained with PERF using an 18 g introducer. Mean lesion volume produced with PERF (80°C for 90 seconds) and an 18 g diameter tip (215 mm3 ) is significantly larger than the respective one produced with MRF (169 mm3 ). Increasing lesioning time to 150 seconds significantly increases the volume (283 mm3 ). Using a 20 g tip produces the smallest lesions at 80°C for 90 seconds with either PERF or MRF, although a lesioning time of 150 seconds makes it significantly larger (207 mm3 ). Limitations: The study is ex vivo and therefore does not account for the dynamic effects of the anatomy and physiology of a living organism. Conclusions: The results indicate that the lesion produced with a cooled-RF system (17 g, 4 mm tip) is significantly larger than that produced with either of the other systems trialed (18 g or 20 g, 10 mm active tip protruding electrode or 16 g, 18 g, or 20 g monopolar electrode). Interestingly, a 16 g, 10 mm active tip monopolar electrode produced a larger lesion than the one produced with the 18 g protruding electrode.