Ex vivo evaluation of force data and tissue elasticity for robot-assisted FESS

The objective of this study was to describe and evaluate soft tissue and bone properties of nasal cavity and paranasal sinuses in ex vivo preparations for a safe robot-assisted endoscope movement during functional endoscopic sinus surgery (FESS). In a first experiment we measured forces exerted by the endoscope during FESS with a force/torque sensor. In a second experiment we used a purpose built device to exert forces on chosen tissue structures. The experiment was monitored by a custom software, which records force of the endoscope and the deformation and the breaking point of tissue. All tests were performed on five formalin fixed cadaver heads. In the first experiment we found that the average force during FESS is 2.21 N and the maximal force is 7.96 N. The force-way-ratio measurement shows highest elasticity for the ethmoidal bulla, followed by the lamina papyracea; however, they break at low forces (> or =6 N). Furthermore the carotid canal seems to have the lowest elasticity but it can tolerate forces up to 30 N. Based on these measurements force thresholds can be defined for robot-assisted endoscope guidance. All thresholds have to be assigned to subregions of the nasal cavity and paranasal sinuses.