Abstract:

Objective    To develop a 3-D finite element (FE) model of anterior screw fixation on lower thoracic vertebra, evaluate and modify the stress of screw and the stick.  Methods    The geometrical model was created by Mimics13.0 based on CT data of T11～12 motion segment from one adult male, and then, the above models were imported into the Ansys11.0 for establishing the 3-D FE of anterior screw fixation on lower thoracic vertebra. The 3D FE models were further imported into Ansys11.0 and analyzed under 500N pressure loading on the upper surface of T11, and 10Nm torque loading for simulating thoracic axial compression, anteflexion, extension, lateral bending and rotation. The Von mises stress of screws and stick were recorded and analyzed statistically the difference of different stress distribution of the screws and stick. Results    It was obviously that, the Von mises of the screw concentrated on the tail of screws, with the bigger stress at the inferior part than that at the superior part. Rotation movement resulted in breakage of the tails of screw and lower part of stick.  Conclusions    Anterior screw fixation system on lower thoracic vertebra will thicken the tails of screws and lower segment of stick. It is necessary to limit patients' activities by a waist-brace protection after operation.

Key words:  Lower thoracic vertebra, Anterior fixaion, Finite element analysis, Biomechanics