Estimation of Penetrated Bone Layers During Craniotomy via Bioimpedance Measurement

Craniotomy is the removal of a bone flap from the skull and is a first step in many neurosurgical interventions. During craniotomy, an efficient cut of the bone without injuring adjoining soft tissues is very critical. The aim of this study is to investigate the feasibility of estimating the currently penetrated cranial bone layer by means of bioimpedance measurement.

A finite-element model was developed and a simulation study conducted. Simulations were performed at different positions along an elliptical cutting path and at three different operation areas. Finally, the validity of the simulation was demonstrated by an ex vivo experiment based on use of a bovine shoulder blade bone and a commercially available impedance meter.

The curve of the absolute impedance and phase exhibits characteristic changes at the transition from one bone layer to the next, which can be used to determine the bone layer last penetrated by the cutting tool. The bipolar electrode configuration is superior to the monopolar measurement. A horizontal electrode arrangement at the tip of the cutting tool produces the best results.

This study successfully demonstrates the feasibility to detect the transition between cranial bone layers during craniotomy by bioimpedance measurements using electrodes located on the cutting tool.

Based on the results of this study, bioimpedance measurement seems to be a promising option for intra operative ad hoc information about the bone layer currently penetrated and could contribute to patient safety during neurosurgery.