Abstract:

Objective　To develop a 3-D finite element(FE) model of bone graft with vertebral debridement and posterior vertebral unit fixed system through ribs of T6~8.　Methods　Spiral CT data of one male patient (172 cm, 71 kg, 39-year-old) with T7 vertebraltuberculosis were imported into computer to develop a 3-D FE model of bone graft with vertebral debridement and posterior vertebral unit fixed system by ribs of T6~8 by Mimics13.0 and Ansys11.0 finite element software. 500N pressure and 10Nm torque to the vertebral surface by 3 kinds of physiological load which simulating flexion, extension and lateral bending were exerted. The stress distribution of fixation devices under different loads was compared.　Results　At the positions of anteflexion and extension, the stress mainly concentrated to screw tail, and stress of the upper screw was greater than the lower screw, stress of the top was always greater than the bottom. At lateral bending position, stress of screw tail was less than that at flexion and extension. Stress was identical at the top and bottom of the vertical rods. For 3 different dynamics at the same points, stress of the extension was greater than anteflexion, stress of the anteflexion was greater than lateral bending at screw tail. Stress of anteflexion was greater than extension, and stress of the extension was greater than lateral bending at E and F points of vertical rods. Stress of vertical rod bottom at lateral bending was the least.　Conclusions　It prones to fatigue fracture at upper screw tail and the top of vertical rods by bone graft with vertebral debridement and posterior vertebral unit fixed system by ribs of T6~8 at the positions of anteflexion and extension.

Key words: Intermediate thoracic vertebra, Vertebral unit fixed by ribs, Finite element, Biomechanics