title: Temperature Prediction Model for Bone Drilling Based on Density Distribution and In Vivo Experiments for Minimally Invasive Robotic Cochlear Implantation.
abstract: Surgical robots have been proposed ex vivo to drill precise holes in the temporal bone for minimally invasive cochlear implantation. The main risk of the procedure is damage of the facial nerve due to mechanical interaction or due to temperature elevation during the drilling process. To evaluate the thermal risk of the drilling process, a simplified model is proposed which aims to enable an assessment of risk posed to the facial nerve for a given set of constant process parameters for different mastoid bone densities. The model uses the bone density distribution along the drilling trajectory in the mastoid bone to calculate a time dependent heat production function at the tip of the drill bit. Using a time dependent moving point source Green's function, the heat equation can be solved at a certain point in space so that the resulting temperatures can be calculated over time. The model was calibrated and initially verified with in vivo temperature data. The data was collected in minimally invasive robotic drilling of 12 holes in four different sheep. The sheep were anesthetized and the temperature elevations were measured with a thermocouple which was inserted in a previously drilled hole next to the planned drilling trajectory. Bone density distributions were extracted from pre-operative CT data by averaging Hounsfield values over the drill bit diameter. Post-operative [Formula: see text]CT data was used to verify the drilling accuracy of the trajectories. The comparison of measured and calculated temperatures shows a very good match for both heating and cooling phases. The average prediction error of the maximum temperature was less than 0.7 °C and the average root mean square error was approximately 0.5 °C. To analyze potential thermal damage, the model was used to calculate temperature profiles and cumulative equivalent minutes at 43 °C at a minimal distance to the facial nerve. For the selected drilling parameters, temperature elevation profiles and cumulative equivalent minutes suggest that thermal elevation of this minimally invasive cochlear implantation surgery may pose a risk to the facial nerve, especially in sclerotic or high density mastoid bones. Optimized drilling parameters need to be evaluated and the model could be used for future risk evaluation.
authors.affiliation: Institute for Surgical Technology and Biomechanics, University of Bern, Stauffacherstr. 78, 3014, Bern, Switzerland. arne.feldmann@istb.unibe.ch.
authors.forename: Arne
authors.identifier: http://orcid.org/0000-0001-9139-9034
authors.initials: A
authors.lastname: Feldmann
authors.affiliation: ARTORG Center for Biomedical Engineering Research, University of Bern, Murtenstr. 50, 3010, Bern, Switzerland.
authors.forename: Juan
authors.initials: J
authors.lastname: Anso
authors.affiliation: ARTORG Center for Biomedical Engineering Research, University of Bern, Murtenstr. 50, 3010, Bern, Switzerland.
authors.forename: Brett
authors.initials: B
authors.lastname: Bell
authors.affiliation: ARTORG Center for Biomedical Engineering Research, University of Bern, Murtenstr. 50, 3010, Bern, Switzerland.
authors.forename: Tom
authors.initials: T
authors.lastname: Williamson
authors.affiliation: ARTORG Center for Biomedical Engineering Research, University of Bern, Murtenstr. 50, 3010, Bern, Switzerland.
authors.forename: Kate
authors.initials: K
authors.lastname: Gavaghan
authors.affiliation: ARTORG Center for Biomedical Engineering Research, University of Bern, Murtenstr. 50, 3010, Bern, Switzerland.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Gerber
authors.affiliation: Department of Clinical Veterinary Medicine, Vetsuisse Faculty, University of Bern, Länggassstrasse 124, 3001, Bern, Switzerland.
authors.forename: Helene
authors.initials: H
authors.lastname: Rohrbach
authors.affiliation: ARTORG Center for Biomedical Engineering Research, University of Bern, Murtenstr. 50, 3010, Bern, Switzerland.
authors.forename: Stefan
authors.initials: S
authors.lastname: Weber
authors.affiliation: Institute for Surgical Technology and Biomechanics, University of Bern, Stauffacherstr. 78, 3014, Bern, Switzerland.
authors.forename: Philippe
authors.initials: P
authors.lastname: Zysset
mesh_terms: D000818:Animals; D015519:Bone Density; D003051:Cochlea; D019929:Cochlear Implantation; D003054:Cochlear Implants; D008416:Mastoid; D019060:Minimally Invasive Surgical Procedures; D008954:Models, Biological; D065287:Robotic Surgical Procedures; D012756:Sheep; D013696:Temperature
keywords: Bone drilling; Cumulative equivalent minutes; In-vivo experimental study; Minimally invasive cochlear implantation; Robotic surgery; Thermal model for bone drilling; Thermal nerve damage