Finite Element Simulation of Pid-Controlled Bipolar Radiofrequency Ablation of Porcine Spinal Muscle

Radiofrequency ablation (RFA) of the medial branch nerve is a widely used therapeutic intervention for back pain originating from the facet joint. However, multifidus denervation is a well-known adverse effect of this RFA procedure. Computational simulations of RFA can be used to design a new multifidus-sparing RFA procedure for facet joint pain. Unfortunately, there is not a computational model available for RFA of porcine spines (a common animal model for the translation of spinal treatments). The objective of this study is to develop and verify a computational model for bipolar radiofrequency ablation of porcine spine muscle. To do this, the electrical and thermal conductivity properties were measured over a temperature range of 20 °C to 90 °C in ex-vivo porcine spinal. A proportional, integral, and derivative (PID) controlled finite element (FE) model was developed and tuned to simulate the ablation process. Finally, tissue temperatures from simulations and experimental ablations were compared. Thermal conductivity values of spinal muscle ranged from 0.33 W/mK to 0.57 W/mK. Similarly, electrical conductivity varied from 0.36 S/m to 1.28 S/m. The tuned PID parameters for temperature-controlled model were Kp=40, Ki=0.01, and Kd=0. A close agreement between experimental measurements of tissue temperature and simulations were observed in the uncertainty range with R-squared values between 0.88 and 0.98. The model developed in this study is a valuable tool for preclinical studies exploring new RFA methods of spinal nerves.