Evaluation of temperature distributions in cadaveric lumbar spine during nucleoplasty

Abstract

In this study, temperature maps were obtained throughout human cadaveric disc specimens (n = 6) during a simulated Nucleoplasty™ treatment. The procedure was performed using the Perc-DL SpineWand™ (ArthroCare, Sunnyvale, CA) inserted through a 17 gage needle into the human cadaveric disc. The device uses a dual mode heating technique which employs a high voltage radio frequency (RF) plasma field to vaporize tissue (Coblation®), followed by bipolar RF current heating for thermal coagulation. The device, with a distal ‘s-curve’, is manipulated manually to create a series of six channels at a 60° angular spacing within a period of 3 min. A computer-controlled, motorized translational system was used to reproducibly mimic the insertion (Coblation) and retraction (rf-coagulation) performed during clinical implementation, with rotation performed manually between each Coblation/coagulation cycle. Transient temperature data were obtained using five multi-junction thermocouple probes (5–8 junctions spaced at either 2 or 5 mm intervals, with 0.33 or 0.56 mm probe diameter) spaced throughout the desired heating volume. Transient temperature curves were obtained from 26+ points throughout the disc, and the data used to calculate accumulated thermal doses. Transient peaks of 80–90 °C were recorded within the discs, with temperatures greater than 60–65 °C measured within a radial distance of 3–4 mm from the introducer (applicator centreline). Accumulated thermal doses of t43 > 250 min were produced at radial distances of up to 6 mm from the introducer. Gross inspection of the discs revealed a narrow region of coagulation along the insertion length. Given these radial thermal penetrations and the possibility for unpredictable positioning during current clinical implementation, high temperatures and lethal thermal doses in small regions outside of the nucleus, or within the bone endplates, may be possible in clinical implementation.