| Spinal anterior internal fixation is widely used in spinal trauma, degeneration, tumors, infections, etc, which were done spinal cord decompression, debridement,in order to reconstruct the anatomical structure,maintain the stability and correct the deformity of the spine. Early anterior fixations were of the poor biomechanical properties, irrational structure and operational difficulties, and so on. In recent years, thoracic and lumbar anterior implants have achieved rapid development. They, which can withstand normal spine biomechanics load, are moving in for the body’s normal anatomical structures, good biocompatibility and little impact of imaging. Anterior internal fixation for the thoracic and lumbar spine, is broadly divided into three categories:one is the screw-rod system, as represented by Kaneda; one is the screw-plate system, as the representative of Z-plate; another one is the screw system, as represented by the MACS-HMA. But none of the screw-rod system, screw-plate system or screw system can meet the clinical needs. In view of this, we developed a full built-in inflatable anterior spinal fixation system, in order to safely, effectively and easily to carry out the anterior Surgery of thoracic and lumbar spine, but also to reduce postoperative complications. At the same time, through independent research and development, the built-in expansive anterior internal fixation system to make homemade, try a large-scale clinical application, effectively reducing the cost of treatment of patients, and create objective economic and social benefits.Part I Anatomic basis of the built-in expansive anterior internal fixation systemObjective To explore anatomic features of T1-L5vertebrae, and provide parameters for the development of the neotype built-in anterior internal fixation with inflation function for thoracolumbar vertebral body.Methods50sets of dry thoracolumbar specimens (T1-L5) were used in this study. No marked deformation, defect or pathological changes were found. The middle transyerse diameters of the thoracolumbar vertebral body(MTD),the middle sagittal diameters’of the thoracolumbar vertebral body(MSD),the middle height of the thoracolumbar vertebral body were measured and analyzed(MH).And obtained95%of the relevant parameters of the reference range.Results As T12for example:MTD is about (33.03±1.85) mm, MSD (25.50±1.46)mm, MH (21.53±1.39)mm.There are5types of the internal fixation:(25、8),(25、10),(30、12)(35、14)、(40、14)Conclusion The designation of the built-in expansive anterior internal fixation system is feasible anatomically. Every part of the fixation device has different parameter ranges, It can be installed successfully to reconstruct the stability of the thoracolumbar vertebral body, which is safe and easy to operate. And the neotype internal fixation system will accord with the spinal structure in the morphological and anatomical structure.Part Ⅱ The research of the built-in expansive anterior internal fixation systemObjective To design the built-in expansive anterior internal fixation system for spinal vertebral body, in order to,on the one hand,can carry out the thoracic and lumbar operation safely、effectively and easily, in the other hand, can reduce the postoperative complications.Methods According to the biomechanical characteristics of anterior thoracolumbar fixation,and the design concept of the industrial, construction areas and thoracolumbar posterior expansional nails,we design the built-in expansive anterior internal fixation system. The fixation is produced by Fule company.Results The fixation system consists of connecting rod, plugs, vertebral nails, and inner core. Screw which points in five models:(25,8),(25,10),(30,12),(35,14),(40,14), is applicable to different groups of people. The shape of the bicortical fixed vertebral nail is cylindrical,and inner diameter is cone. The pitch of vertebral nail is3mm,and the thread depth is0.5～0.85mm ranging from cutting-edge to the end.The diameter of the connecting round bars is6.5mm.The expansion functionof the the vertebral body nail can be achieved, when the inner core is screwed into the ertebral body nail,and enhancing the holding force on the vertebral body.Conclusion The built-in expansive anterior internal fixation system for spinal vertebral body,Which designs with scientific theory and practical basis, is able to reconstruct the stability of the thoracolumbar spine.Part III Three-dimensional biomechanical test of the built-in expansive anterior internal fixation systemObjective We perform the three-dimensional motional stability test,in order to evaluate the effect of the built-in expansive anterior internal fixation system in the reconstruction of the thoracic and lumbar.Methods18pig spinal specimens (T14-L3) were divided into three groups (6per group) and subjected to L1corpectomy. One of three fixation methods was applied to the left of the vertebra(T15-L2) in each group:the built-in expansive anterior internal fixation system,Z-plate and Kaneda system.Each spine was tested in three different scenarios:1)intact spine;2) partial L1corpectomy;3)after partial L1corpectomy with graft and stabilization with three alternative instrumentations.The top of the embedded specimens were connected with three-dimensional spine loading disc drive and the base of the embedded specimens were fixed lower working platform in the testing machine.The range of motion of different groups was measured by a three dimensional spinal stability test in the MTS material testing machine.Each group samples were flexion and extension, lateral bending and rotation around the direction of motion stability, implementing pure couple moment load, load of6.0Nm, maintaining30s as a cycle.Measured before exercise, every condition, the specimen is loaded to the maximum torque of6.0Nm, and then uninstall, also repeated3times, loading/unloading cycle after the data collection form3times load/unload cycles to the cervical spine viscoelastic removal of the effects to a minimum, be more stable the results of cervical spine movement when the load to6.0Nm time for30seconds, allowing the specimens creep movement kinematics in the three-dimensional biomechanical test after loading. Directly obtained by the computer coordinates for each marker movement, calculated for each specimen using EVaRT software segment angular displacement, the angular displacement of the vertebral body is derived by adding the cervical spine range of motion.The moment was applied with±6.0N.m loads in flexion/extension, left/right lateral bending, and left/right axial rotation on the three-dimension motion stability test. Multi-level motion was measured by using Motion Analysis Motion Capture System. The motion measure system included six infrared camera placed around cervical specimen and used specialized acceptable infrared, sphericity markers. Six markers were rigidly attached to each vertebral level in noncolinear position and oriented to permit detection by infrared camera. Each marker motion coordinate was calculated by computer using EVaRT software and angular displacement parameters were calculated, including the range of motion(ROM),neutral zone(NZ),and elastic zone(EZ),in flexion and extension, right/left lateral bending, and left/right rotation. The results obtained are used SPSS13.0statistical package for statistical treatment, range of motion within the3groups were compared using repeated measures analysis of variance, if not to meet the spherical assumption, the report uses Greenhouse-Geisser results; further multiple comparisons using the LSD method(Least-Significant Different).Range of motion among the three groups after the fixation was used to compare changes in the single factor analysis of variance (one-way ANOVA). If not meet the heterogeneity, analysis of variance used Welch method missing correction; further multi-LSD was used to compare method (Least-Significant Different). Inspection level a=0.05.Results The full built-in expansive spinal anterior fixation specimens group (column group), Kaneda group, and Z-Plate group in flexion, extension, left bend, right bend, sinistral and dextral status:compared with the normal group, P<0.05, significant difference; versus injury group, P<0.05, significant difference.So all the three internal fixation can rebuild the thoracolumbar stability. The was no significant difference of the range of motion among the full built-in expansive spinal anterior internal fixation group, the screw-rod fixation group and the nail-plate fixation group on the direction of flexion(F=0.044, P=0.957) extension(F=0.410, p=0.671) and right lateral bending(F=0.121, P=.887), P>0.05;The difference of the range of motion on the direction of left lateral bending(F=9.640, P=0.002),Left axial rotation(F=5.782, P=0.014) and right axial rotation (F=4.189, P=0.036) were significantly different. The difference of the the range of motion between the full built-in expansive spinal anterior internal fixation group and the screw-rod fixation group was significant(P<0.05) on the direction of left lateral bending(P=0.001),Left axial rotation(P=0.004) and right axial rotation(P=0.011).Although the range of motion of the full built-in expansive spinal anterior internal fixation group was larger than that of the nail-plate, there was no difference between them(P>0.05)on the direction of left lateral bending(P=0.240),Left axial rotation(P=0.100) and right axial rotation(P=0.153).Conclusion All the three model anterior thoracolumbar instrumentations can restored the stability. The BEAF system showed lower stability compared to the Kaneda system,.but the same stability with the Z-plate system.Part IV The insertion torque and pullout strength test of the built-in expansive anterior internal fixation systemObjective To measure and compare the insertion torque and pullout strength of the built-in expansive anterior internal fixation system (BEAFs) and to evaluate the screw purchase of BEAFs screws.Methods Twenty-four L1vertebral bodies were classified into A, B, C,D4groups randomly,6pedicles per group. Ordinary screw(30mm,6.0mm), unexpensive BEAFs screw (30mm,12mm),BEAFs screw (30mm,12mm) and BEAFs screw (30mm,12mm) were implanted into the pedicle of each group respectively. Firstly,the torques experiment was done in group A, group B, Group C; Then,Pull-out strength test was done in group A, group B, Group D.Results The difference of the maximum pullout force among the three groups,by analysis of variance, was significant(F=29.121,P=0.000).The difference of the maximum pullout force between A and B groups was significant(P=0.019).There was significant difference of the maximum pullout force between C and B groups(P=0.002),and also between C and A groups(P=0.000).The difference of the maximum torques among the three groups,by analysis of variance, was significant(F=5.509,P=0.016). There was no significant difference of the maximum torques between B and A groups(P=0.087),and also between B and D groups(P=0.159).The difference of the maximum torques between D and A groups was significant(P=0.005).Conclusion The built-in expansive anterior internal fixation system (BEAFs) can reconstruct the immediate stability of the thoracolumbar spine, but the design needs further improvement. |
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