| In this study,we investigated the effects of the position and numbers of crosslinks on the internal fixation of spine by the biomechanical test in the model of thoracolumbar pedicle splitting in adult sheep.And then through adding the additional crosslinks,make up the instability caused by inserting the pedicle screw to crack the pedicle of vertebral arch.Through manual screening and X-ray fluoroscopy to exclude lesions,the vertebral compression fracture was performed in the L1 vertebral body using the Chiba’s method from 60 fresh thoracic and lumbar vertebrae samples of sheep(T13-L3),which were randomly divided into 6 groups(A,B,C,D,E and F).Bilateral pedicles of vertebral arch of T14 and L2 were inserted pedicle screws,connecting titanium rods to fix T14-L2 segments.Then the samples of group B,C,D,E and F were removed a quarter of right side of lateral T14 thoracic pedicle cortical(10mm length,5mm width)until exposing outer screw thread and clearing thread within the bone which were considered as the pedicle cortex splitting model.Finally,each group was fixed on different numbers of crosslinks:group A(0 crosslink,Intact),group B(0 crosslink,NCL),group C(1 crosslink,1/2 of the rods,MCL),group D(1 crosslink,1/3 of the rods close to T14,PCL),group E(1 crosslink,2/3 of the rods away from T14,DCL)and group F(2 crosslinks,1/3 and 2/3 of the rods respectively,TCL).After that all samples were subject to 10000 times of fatigue test with 1.5 Hz load on the HY-3080 computer-control electronic universal test machine and HY-1000 NM computer-control torsion test machine,then the axial compressive stiffness,range of the motion(ROM)of the 6 directions(flexion,extension,left and right lateral bending,left and right axial rotation)and the maximum pullout strength of the screws of the T14 pedicle cortex splitting were measured and compared of the 6 groups.Comparison of Axial Compression Stiffness of 6 Specimens:the axial compressive stiffness in group A,C,D,E and F were significantly bigger than in group B(P<0.05);the axial compressive stiffness in group C,D and E were no significantly difference in group F(P>0.05);the axial compression stiffness in group C,D and E showed no statistically significant difference(P>0.05);the axial compressive stiffness in group F were smaller than in group A.Comparison of range of motion(ROM)of 6 Specimens:ROM of flexion/extension(coronal axis),lateral bending(sagittal axis)and axial rotation(vertical axis)in group B were significantly higher than in group A,C,D,E and F(P<0.05);ROM of left and right axial rotation in group C,D and E were significantly bigger than in group F(P<0.05),but ROM of flexion,extension and lateral bending were no significantly difference in group F(P>0.05);ROM of flexion,extension,lateral bending and axial rotation in group C,D and E showed no statistically significant difference(P>0.05);ROM of flexion,extension,lateral bending and axial rotation in group A and F showed no statistically significant difference(P>0.05).Comparison of the Maximum Pullout Strength of 6 Specimens:the maximum pullout strength in the rest groups were significantly bigger than in group B(P<0.05);the maximum pullout strength in group C,D and E were significantly smaller than in group F(P<0.05);the maximum pullout strength in group C,D and E were no significantly difference in group F(P>0.05);the maximum pullout strength in group F were smaller than in group A.When the Pedicle Cortex Perforation,internal fixation stability decreased significantly.Adding one crosslink can improve the stability of the pedicle cortex perforation;adding two crosslinks can approximately achieve the same stability as the pedicle screw fixation with no pedicle cortex perforation;the location of one crosslink has no statistical significance in the short segment of spinal fixation no matter in the proximal,distal end or the middle of the vertical rod. |
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