Biomechanical Study Of The Influence Of Stability For The Pedicle Screws Fixation By Injured Vertebral Screw In The Spine Posterior Fixation Of Pedicle Screw-rod System When The Pedicle Cortex Perforation

This research through the artificially constructed pedicle cortex splitt- ing model, to study the pedicle cortex splitting effect on fracture of vertebr- al stability and effect,according to the results of further studies on the effect of different pedicle screws on the screw fixation stability mode.Pre- liminary studies using fresh specimens of adult sheep spine biomechanical experiments, using fresh sheep spine specimen 20,intercepting the(T13 ~ L3) spinal segments, beyond A tumor,fracture and congenital spinal defor- mity, and so on and so forth, the specimens were randomly divided into A,B two groups,making single vertebral compression fracture model respectively in A group and B group specimens of L1 vertebral body,then alone on the B group were T14 thoracic pedicle for left lateral(1/4-1/2) resection,as pedicle splitting vertebral fracture model[1].The model of two groups were inserted the screw and the inserting depth of the screw was the total length of the screw. After the samples of two group was fixed, The model of10000 fatigue experiments were performed in the biomechanical testing machine, The range of motion(ROM) of the four directions-anteflexion, retroflexion, left and right lateral curvature and the drawing force of the screw was measured and the difference was compared. The results showed that, according to the results of 10000 times after fatigue experiment, twoexperiments compare to:group A range in all directions were less than group B, the difference is statistically significant(p <0.01). the ROM value of the four directions-anteflexion,retroflexion, left and right lateral curvat- ure on group A is(1.81±0.14)°,(1.68±0.37)°,(4.08±0.41)°,(4.18±0.12)°; the ROM value of the four directions-anteflexion,retro- flexion, left and right lateral curvature on group B i S(4.49±0.40)°,(3.72±0.51)°,(6.67±0.64)°,(6.73±0.58)°;Maximum pull screw two groups of the experimental specimens for output comparison: In group A bigger than group B,the difference is statistically significant(p < 0.01), The maximum pull-out force of Group A is(252.34 + 51.27) N; The maximum pull-out force of Group B is(115.50 + 36.74) N。In the preliminary study on the basis of experiments to further investigate the effect of vertebral pedicle screw placement within the pedicle spinal fixation stability after splitting.selecting 36 fresh sheep spine specimens, includ the interception(T13~L3) of the spinal segment, in the removal oftumors, and congenital deformity of spine fracture, etc, which were randomly divided into A, B, C, D four groups, A, B group with the same treatment of the preliminary study, C, D group treat-ed the same as B group, in C group and D group of L1 vertebral body are single vertebral compression fracture model,then lateral pedicle for the two groups of T14 of thoracic left(1/4~1/2) resection, as pedicle splitting verte- bral fracture model, Then four specimens pedicle screw placement, the inserting depth of the screw was the total length of the screw,Except that the group C four pedicle screws after implantation,after the left vertebral pedi- cle screw again into one, and D group into four pedicle screws, on both sid- es of the vertebralpedicle screws were inserted, namely group C group into five screws, D group into six screws groups.(Four groups were performed fatigue test of 10 000 times by(300±105)N load.Comparison of four models of the axial compressive stiffness,T14 vertebral pedicle screw pull-out strength and split side scope of activities of four directions. After the10000 flexion, extension movement, The results showed, the axial compressive stiffness of A, C, D group was significantly greater than group B, the difference is stat- istically significant(P<0.01), the axial compressive stiffness of C, D grou- p was significantly greater than group A, the difference is statistically sign- ificant(P<0.01), the axial compressive stiffness of C, D two groups was not statistically significant(P> 0.05).The maximum drawing force of screws in the other three groups were significantly lower than those in gro- up A(P<0.01), The drawing force in gro- ups B、C and D had no significant difference(P>0.05).The four groups of the experimental specimens activity comparison: Group B specimens model flexion, lateral bending four directions range of motion were significantly higher than A, C, D(P <0.01); and the maximum range of motion in four directions of the C and D groups were lower than that of group A(P<0.01); there is no significant difference between the activity of C, D two groups(P>0.05).The results of this study suggest that,Pedicle cortex split will reduce the stability of pedicle screw fixation, vertebral pedicle screw fixation can increase the stability of the split within the pedicle, or even better than the stability of the stability of pedicle intact.