RESUMO
Objective: To explore and evaluate the biomechanic relationships between different depth of pedicle screw penetration with the sagittal plane reconstruction in thoracolumbar fracture. Methods:Six fresh cadaveric specimens of lumbar spine from L_1 to L_3 were used to make the model of thoracolumbar fracture. The system of universal spine system( USS )pedicle screw was adopted with the 6 mm diameter of screw. Each of two Schanz screws was implanted into the pedicles of L_1 and L_3 A canulated screw was fixed into the former of vertebral body in L_1 and L_3, and the distance of the two canulated screws was taken as the normal height. The axial loads were given while the pedicle screws were implanted at the depth of D1, D2 and D3, and the distance of the two canulated screw was measured as well as the distance was reduced to the normal height by axial load. The index measured included of the depth of pedicle screw penetration, the height of fractured vertebral body and afterload. Results: Along with the increasing of afterload, the height of injured vertebral body was increased accordingly, but the extent was different at three depth of pedicle screw penetration (D1, D2, and D3). While the injured vertebral body was reduced totally (reduced distance 0.00 mm), there was (2 630±13) g of afterload needed in Dl depth, and (2 339±61) g and(2 221± 164) g of afterload in D2 and D3 depth respectively. There was significant difference in distance between D1, D2 and D3 (P 0.05). Conclusion: There is a relationship in the depth of pedicle screw penetration, the capacity of reduction and sagittal plane reconstruction. The depth of pedicle screw had a significant effect on the capacity of reduction for the injured vertebral body, which would be the best option in biomechanics when the pedicle screw was implanted more than 1/2 pedicle or all of it.
