The Design And Biomechanical Comparison Study Of A New Type Of Thoracolumbar Pedicle Screw

Objective: To improve the fixation strength of thoracolumbar pedicle screws, we design a new type of pedicle screws based on general pedicle screws design basis. By fixing new and general pedicle screws in fresh calf lumbar specimens respectively, biomechanical tests were performed on each specimen. Comparing the differences of anti- press strength of specimens to prove that the differences of fixation strength existed in new and general pedicle screws and to provide certain theoretical basis for clinical application of new screws.Methods: Based on the general pedicle screws design basis,we design new type of pedicle screws by improving screw shape, screw, tapping screw head and "U" shaped bearing. The new pedicle screws are designed with double screw thread, including cortical bone screw and cancellous bone screw. "U" shaped bearing which is the tail of screw, contains trapezoidal thread locking technology. Tapping screw head with guide groove allow nailing directly without tapping. The design of the whole system adopts low remember.Choosing 20 fresh calf lumbar spine specimens(L2-L5) in total, under X-ray fluoroscopy, excluding spinal trauma, tumor, deformity and bone hyperplasia disease of the spine. Carefully remove lumbar soft tissue, supraspinal ligament and anterior longitudinal ligament retained, embedding the head and tail end of vertebra(L2 and L5) with denture base material, keep embedded specimens positioned perpendicular to horizontal plane.According to the four states:normal, fracture, general screws fixation and new screws fixation, all specimens are divided into four groups: group A(normal group), group B(lumbar fracture group), group C(general group) and group D(new group).All specimens are conducted biomechanical test sequentially in HD-5000 B multi-function material testing machine; the axial compression force is composed from 0 N increased to the maximumcompression force 5000N;compression rate is set to 3mm/min;we describe each specimens compression deformation with displacement(mm), record deformation quantity of specimens under different loads, analyse the relevant data statistically.Results: Under any given loads, the comparison of any two groups is consistent with the homogeneity test of variance(P>0.05); the deformation quantity of four groups are not all the same(P<0.05). Under any given loads, fracture group deformation quantity is higher than normal group deformation quantity and the difference is statistically significant(P<0.05). Under any given loads, general group, new group deformation quantity are smaller than that of normal group and fracture group and the difference is statistically significant(P<0.05). Under any given loads, general group deformation quantity is higher than new group deformation quantity and the difference is statistically significant(P<0.05).Conclusion: Both general and new pedicle screws can fix calf spine specimens effectively and the new pedicle screws prove more fixation strength than general pedicle screws prove.