| Abstract:Objective:In this study, we use samples of porcine thoracolumbar spine to imitate burst fracture of thoracolumbar operated by anterior approach. Operative treatment consisted of subtotal corpectomy, followed by titanium mesh cages (TMCS) bone fusion and internal fixation with screw-rod or screw plate system, then a biomechanical testing machine was used to test the stiffness and stability.Test data was recorded and analyzed for comparison and to explore its biological force function and variation. Providing a theoretical basis, to preserve the blood supply of spinal vertebrae in the operation.Methods:8 specimens of T10～L4 thoracolumbar spine in pigs, breeded 6-8 months and weighing about 130 kg, were used. Specimens were detected by positive, lateral X-ray and bone densitometry preoperatively, excluding osseous congenital malformation and Osteoporosis. After specimen were harvested, they were wrapped with Saline gauze immediately, encapsulated with double plastic bags, stored at-20℃freezer. Before testing, the spines were thawed at room temperature.Carefully remove outer muscle tissue attaching to ligament and all other connected structures, exposed but not to damage small joint capsule, and intervertebral disc, small facet, joint capsule’s integrity should be preserved at the attention. Then they were randomly divided into 2 groups, each of them were four specimens. The first group (A)was operated by L1 subtotal corpectomy TMCS bone fusion and internal fixation with screw rod system; the second group(B) was operated by L1 subtotal corpectomy TMCS bone fusion and internal fixation with screw plate system. Operation was referenced to Professor Wang Qing "Operation method of thoracolumbar modified anterior approach". Way of implanting screw was referenced to Professor Rao Shucheng "Operation method of the Spine Surgery". The entrance point was 8 10mm ahead of the vertebral posterior wall,8～10mm under the upper centrum upper endplate,8～10mm above the lower centrum lower endplate, 10°to anteversion after it had been drilled into, opposite side cortex should be penetrated. The experimentation was operated by the same person, with the same moment inserting into internal fixation devices.T13, L3 vertebral body of thoracic and lumbar spines were embedded with dental bone cement and kept neutral position, maintained the upper paralleling to lower surfaces in order to ensure the force line and homogeneity of loading. Both specimens were placed in the loading system of Japanese Shimadzu microcomputer control electronic universal testing machine for the left axial rotation (LR) load test, the right axial rotation (RR) load test. First,80N was set for eliminating the influence of specimen’s effects of relaxation and of creep time. Each experiment was carried out by loading, unloading, reset, next experiment was also carried out by loading, unloading, reset after 10 minutes’relaxation. Each experiment was repeated 3 times and averaged its results.Measured torsion angle among T14 and L2 by the AMPV-ID high-precision torque indicator, the computer could directly output the data.After changing specimens or its position,pre-loaded should be done, and then unloaded to zero. With torsion machine made by Biomechanics Laboratory of Sichuan University, for simulating human’s thoracic and lumbar,the specimen were tested in four directions of physiological motion, flexion (FL), extension (EX), left bending (LB), right bending (RB)were all tested.Every direction displacement was measured by the KG-101 high-precision raster digital display instrument,computer output data, which were calculated and analyzed by professionals, The included angle changing values caused by steel needle fixing into specimen were obtained in four direction under 5Nm,7Nm load. Specimen should be taken a rest and given 80N with Universal Testing Machine for eliminating the influence of specimen’s effects of relaxation and of creep time after six direction loading experiment had been done, then axial load of 0 to 900N was given. Record the axial displacement among T14 and L2. During the experiment, specimens were kept moist with regular spraying of normal saline for reducing degeneration caused by experiment, so that the results were more reliable and more comparable.Statistical analysis:The measured data was analysed with SPSS 14.0 statistical software under the normal distribution. For comparison between the two constructs, a one-way analysis of variance(ANOVA) was performed with significance set at the alpha 0.05 level.Results:(1) With the increasing load in the axial, load,the displacements in these two specimen were both increased betweenT14 and L2. Changing values of displacements under 100,300,500,700,900N for comparison,the displacements’increasement of screw-plate system was more significant and differences(p<0.05).It showed screw rod system was better than screw plate system against axial load.(2) Left and right rotary moment under 1,2,3,4,5Nm was given to two sets of specimens separately. We measured torsion angles among T14-L2, and did statistical analysis.It implied that the torsion angles of screw-rod system were all less than that of screw-plate system,the difference was significant (p＜0.05), and showed screw-rod system was better than screw-plate system in left and right circumgyrating.(3) 5Nm,7Nm load of flexion and extension was given to specimens separately, and we compared the angles caused by markers planting in this two specimens. The variety of screw-rod system was less than screw plate system, the difference was significant (p＜0.05), which showed screw-rod system was more stability. (4) Specimens were given 5Nm、7Nm load of left and right lateral bending separately, and we compared the angles caused by markers planting in this two specimens. Screw rod system and plate system did not differ significantly (p> 0.05).Conclusion:In the axial direction load, left and right rotary moment, and the loads of flexion and extension, the stability of the screw-rod system was better than screw plate system, the difference was significant (P＜0.05). In the left and right lateral bending, the angles between two specimens was not significant (P>0.05) under the same load. |
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