Institute for
Robotics and Process Control

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Homogeneous FE Modeling of the Inferior Turbinate

Simulating inferior turbinate deformations during opening of the maxillary sinus ostium


The opening of the maxillary sinus ostium is a standard surgical procedure performed in endonasal surgery. As represented in the first picture, the surgeon moves the endoscope from the nostril (1) by the middle nasal passage (2) pressing the top of the inferior turbinate (3) in direction to the ostium of the maxillary sinus (4). Using Finite Element Method (FEM) we have simulated the mechanical pressure applied on the inferior turbinate (IT) during this surgical procedure. We have reconstructed the endonasal approach for the maxillary sinus from CT images of a patient head. It was reconstructed using landmarks settled starting on the nostrils and ending in the natural openings of the maxillary sinus.

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1) Visualization from CT images in coronal reconstruction of paranasal sinuses of a cadaver head showing maxillary (orange), ethmoidal (green) and the right frontal sinus (purple). The yellow points indicate the pathway over the inferior turbinate.
2) 3D structure of the IT mathematically modeled using Ansys, the mesh consists of 16132 nodes and 77221 elements. The IT is relatively fixed in the lateral wall of the nasal cavity being anteriorly attached to the conchal crest of the maxillary sinus.
3) The two boxes show the two possible endoscope-tissue contacts from top: punctual and linear.

Finite Elemente Analysis of endoscope/turbinate contacts


For the simulation, based on the surgeon`s experience, we have selected three main cases of endoscope/tissue contacts possible in the top of the IT: punctual contact (when the endoscope just touch the IT or loading in just one node of the IT model), horizontal linear contact (when the endoscope press the IT in horizontal direction or loading in a line of nodes of the IT model) and vertical linear contact (when the endoscope makes a curve in direction of the maxillary sinus ostium, indicated in rose, in this case the loading is also in a line of nodes but in the vertical direction). The figure below shows the posterior, anterior and posterior segment (inner) views of compressive stress distribution of the IT, i.e., the internal resistance to the deformation produced in the IT model due to three different axial compressive endoscope contact of 5N. The unloaded or little stressed regions are in blue. The areas under high load are in yellow to red.

Videos:

Contact between endoscope and IT punctual, horizontal linear and vertical linear.


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The Finite Element Analysis (FEA) could determine which endoscope contact yields more stress in the IT model. The qualitative and quantitative results lead us to believe that the vertical linear contact of the endoscope (third case) reveal a more concentred stress distribution (76%) on the posterior segment of the IT. This means that during endonasal surgery, under this endoscopic contact, this is the region of the IT that presents more fragility.
This pilot-study represents a first attempt to simulate the complex deformation patterns of the nasal cavity and paranasal sinuses due to endoscope contact during endonasal surgery. In this work, we proposed a simplified homogeneous FE model that resembled the general complex geometry of the IT and yet enabled FEA of various parameters related to its deformation due to endoscope contact. Further models should incorporate more structural features, such as inhomogenenity, different anatomical variations or pathological conditions.

Slides


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