Computer modelling of RF ablation in cortical osteoid osteoma: Assessment of the insulating effect of the reactive zone

Abstract

Purpose: The aim was to study by computer simulations the insulating role of the reactive zone surrounding a cortical osteoid osteoma (OO) in terms of electrical and thermal performance during radiofrequency ablation (RFA). Material and methods: We modelled a cortical OO consisting of a nidus (10 mm diameter) enclosed by a reactive zone. The OO was near a layer of cortical bone 1.5 mm thick. Trabecular bone partially surrounds the OO and there was muscle around the cortical bone layer. We modelled RF ablations with a non-cooled-tip 17-gauge needle electrode (300 s duration and 90 °C target temperature). Sensitivity analyses were conducted assuming a reactive zone electrical conductivity value (σ_rz) within the limits of the cortical and trabecular bone, i.e. 0.02 S/m and 0.087 S/m, respectively. In this way we were really modelling the different degrees of osteosclerosis associated with the reactive zone. Results: The presence of the reactive zone drastically reduced the maximum temperature reached outside it. The temperature drop was proportional to the thickness of the reactive zone: from 68 °C when it was absent to 44 °C when it is 7.5 mm thick. Higher nidus conductivity values (σ_n) implied higher temperatures, while lower temperatures meant higher σ_rz values. Changing σ_rz from 0.02 S/m to 0.087 S/m reduced lesion diameters from 2.4 cm to 1.8 cm. Conclusions: The computer results suggest that the reactive zone plays the role of insulator in terms of reducing the temperature in the surrounding area.

• Computer modelling
• cortical bone
• finite element method
• osteoid osteoma
• radiofrequency ablation
• reactive zone

Declaration of interest

This work was supported by a grant from the Agencia Nacional de Promoción Científica y Tecnológica de Argentina (Ref. PICT-2012-1201), and by the Spanish Programa Estatal de Investigación, Desarrollo e Innovación Orientada a los Retos de la Sociedad under grant number TEC2014-52383-C3-R (TEC2014-52383-C3-1-R). The authors alone are responsible for the content and writing of the paper.