Background and objectives: Bimaxillary advancement of the upper and lower jaw is a successful surgical treatment for OSA that opens the airway at the base of the tongue. However, the amount of jaw advancement required to successfully treat a patient is difficult to determine prior to the operation. Simulation of airway changes based on an individual patient’s 3-D CT scan would allow pre-operative assessment of the degree of jaw advancement necessary to treat the OSA and thus contribute to reduced mortality and improved outcome. We present a simulator for interactive, 3-D modeling of airway deformation in response to a bimaxillary advancement.
Methods: To model the soft-tissue deformation, we apply the total Lagrangian implicit dynamics (TLID) formulation of the finite element method (FEM) to a linear tetrahedral mesh with the St. Venant-Kirchhoff constitutive law. We assemble the mass and stiffness matrices and solve the linearized system on a GPU. We implemented both a tetrahedral volume shader and a single-pass wireframe shader to render the deformations real-time.
Results: The simulation performs fast enough to allow real-time user interaction with smaller meshes, with update rates of approximately 50 Hz for meshes of less than 1000 vertices. Using a homogeneous, isotropic material, we were able to simulate a deformation of the airway with a final volume that closely compares to the actual post-op airway volume. Furthermore, the rendering of the estimated surface changes to the face reasonably approximate the actual post-op aesthetics.
Conclusions: Based on a comparison between simulated results and actual pre-op and post-op data, we conclude that our simulator provides clinical value in both estimating the change in the airway volume and evaluating the facial appearance resulting from a bimaxillary advancement.
Key words: OSA; airway simulation; 3D; finite elements