| Background The techniques of pedicle screw implantation is one of key factors for reconstrucntion of the sagittal plane balance in thoracolumbar fractures. Some researchers demonstrated that the conditions of pedicle screw implantation had several effects on reductions of fracture and biomechanics stability; however, there was not reports about the penetration depth of pedicle screw on the capacities of reduction for injuried vertebral body.Objective To explore and evaluate the relationship of different depth of pedicle screw with the biomechanics of sagittal reconstruction in thoracolumbar fracture.Materials and Methods Six fresh cadaveric specimens of lumbar spine from L1 to L3 were used to make the model of thoracolumbar fracture. The system of USS pedicle screw was adopted with the 6 mm diameter of screw. Each two Schanz screws were implanted into the pedicles of L1 and L3, a canulated screw was fixed into the vertebral body of L1 and L3 each., and the distance (h) of two canulated screws were 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 (h') of the two canulated screw were measured as well as the distance (h) was reduced to the normal height by axial load. The specimens were dived into six groups, and every loading were repeated three times. The index measured included of the penetration depth of pedicle screw, the height of fractured vertebral body and afterload. The system of SPSS10.0 was used for statistic analysis.Results There was significant difference (P<0.01) of afterload at D2 (the penetration depth of pedicle screw 1/2 pedicle ) and D3 (the penetration depth of pedicle screw all pedicle) comparing to D1 (the penetration depth of pedicle screw at the posterior boarder edge). While the penetration depth of pedicle screw was at the posterior boarder edge, more afterload was necessary to reduce the injured vertebral body; with the pedicle screw being implanted deeper, as the pedicle screw was at more than 1/2 pedicle, less afterload was needed to reduce the above height of injured vertebral body. The results showed that deeper of pedicle screw, less afterload needed. While the injured vertebral body was reduced totally (reduced distance 0.00mm), there was 2630±13g of afterload needed in D1 depth, moreover, 2339±61g and 2221±164g of afterload in D2 and D3 depth respectively. There were significant difference of D1 comparing to D2and D3(P<0.01), however, there was not significant difference between D2 and D3(P>0.05).Conclusion There is a relationship of the depth of pedicle screw with the capacity of reduction and sagittal plane reconstruction, the penetration depth of pedicle screw has a significant effect on the capacity of reduction for the injured vertebral body. It is the best option in biomechanics that the pedicle screw is implanted more than 1/2 pedicle or all of it. |
