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BACKGROUND:

At present,there is lack of relevant biomechanical model for the T6-T7-T8 rib-vertebral fix unit.In addition,there is no support of parameters of basic studies on reasons and reasonable explanation of screw breakage,poor quality of bone fusion and adjacent segment degeneration.

OBJECTIVE:

To develop a three-dimensional finite element model of bone graft with vertebral tuberculosis debridement and posterior rib-vertebral unit fixed system through tuberculosis of thoracic spine (T6-8),and to analyze the stress so as to improve it.

METHODS:

Spiral CT data of one male patient (172 cm,71 kg,39-year-old) with T7 vertebral tuberculosis were imported into computer to develop a three-dimensional finite element model of bone graft with vertebral debridement and posterior vertebral unit fixed system through tuberculosis of T6-8 by Mimics 13.0 and Ansys 11.0 finite element software.500 N pressure and 10 N?m torque were loaded to the vertebral body by 3 kinds of physiological loads which simulated flexion,extension and lateral bending.The stress distribution of fixation devices under different loads was compared.RESULTS AND

CONCLUSION:

At the positions of anteflexion and extension,the stress mainly concentrated to screw tail,and the stress of upper screw was greater than the middle and lower screws.For connecting rods,the stress of the middle was always less than the lower middle and the middle stress was zero.At lateral bending position,the stresses of upper and middle screw tail were quite,and the unilateral stress of connecting rod was also equivalent.For three different dynamics at the same point,the stress of middle connecting rod increased in the lateral bending motion,and the stress of lower screw tail was equivalent.These data suggested that it is prone to fatigue fracture at upper screw tail by bone graft with vertebral tuberculosis debridement and posterior rib-vertebral unit fixed system through tuberculosis of thoracic spine (T6-8) at the three positions of anteflexion,extension and lateral bending.The lower connecting rod at the positions of anteflexion and extension and the middle connecting rod at the position of lateral bending easily cause fatigue fracture.