| Objective:To analyze the feasibility of a minimally invasive lumbosacral fusion and fixation device via presacral approach used to the native, and to initially design the device fit to the native and its modus operandi, research its characteristics in the mechanics of materials and mechanical function, and reveal its influence and significance in the stabilization of the lumbosacral vertebrae. This study is focus on the design and evaluation of the device, which will offer basic experimental information for its further development and clinical application.Method:①To analyze the feasibility of the minimally invasive device used to the native by statistically measuring and observing the related anatomical data of lumbosacral vertebrae in the plain films of normal male and female experimental groups, and conferring to the related foreign surgery.②To design the minimally invasive device fit to the native and its modus operandi at the base of anatomical data and feature of the native lumbosacral vertebrae, according to the basic requirement of humanized design and the design code in Ergonomics.③To research its characteristics in the mechanics of materials and mechanical function by the finite element analysis.④To reveal its influence and significance in the stabilization of the lumbosacral vertebrae through examining the biomechanical changes in the lumbosacral functional unit of experimental animal under the different conditions.Result:①It could be discovered in the statistical data of lumbosacral vertebral radiology anatomy in the experimental objects, which a surgery approach corridor was existent, consisted with the essential requirement of the device. But it was different with the foreign in the points of entry on the skin and sacrum.②It has been initially designed that the minimally-invasive presacral lumbosacral fusion and fixation device. The reasonable optimized structure belonged to the device in theory, which could achieve the basic operative procedures successfully in L5–S1 intervertebral space, such as the discectomy, interbody distraction, interbody fusion and fixation, and so on. At the same time, the device could preserve the integrity of the paravertebral tissue, surgical approach tissue and natural spinal structure with minimally invasive injury, such as the muscles, ligaments and vertebral plates etc.③The characteristics of the designed device have been displayed by the finite element analysis that were in the mechanics of materials and mechanical function. Whether made of stainless steel or titanium alloy, the device always met the designing requirement of strength, under the physiological and extreme load states of the lumbosacral vertebrae. And the characteristics in mechanical function were basically identical.④The axial compressive stiffness of the lumbosacral functional unit was obviously increased by using the designed device to the experimental animal model. The ROM in flexion was marked reduced from the normal when the spinal posterior column was stable, and the similar reductions in ROM were observed in extension, right LB, left LB, CK torsion and CCK torsion. When the spinal posterior column had the unilateral isthmectomy, the rage of torsional motion in the rotation to the healty side was increased, but it was still visibly lower than the normal's. With the biolateral isthmectomy in the spinal posterior column, there was an evident increase in the rage of torsional motion in the both rotations, and it was close to the normal level. While fixed with the pedicle screws, the functional unit immediately had a more marked reduction in the ROM than before.Conclusion: It is feasible to the normal native that the minimally invasive lumbosacral fusion and fixation device is used via presacral approach. This is determined by their anatomy construction of the lumbosacral vertebra. The actual operating mode is different with the foreign, and has its own feature. The initially designed device combines four main characteristics, including native application, optimized structure, achieving the basic lumbosacral operative procedures successfully and minimally-invasive injury. It has been attained by the device in theory that the basic requirement of humanized design and the design code in Ergonomics. Whether the making material is stainless steel or titanium alloy, the design of the device always meets the requirements of strength under the physiological and extreme load states of the lumbosacral vertebrae. And basically identical characteristics are displayed in mechanical function. The new designed device has a kind of obvious function to increase the axial compressive stiffness of the lumbosacral functional unit. When the spinal posterior column is stable, the motion of lumbosacral vertebrae is so markedly limited by using the device to strengthen of the unit stability. This function is weakened, especially the limitation in the torsional motion, as the spinal posterior column changes to be partly stable. While it is still firm enough to strengthen the stability visibly. But when the absolute instability occurs in the spinal posterior column, its function of the limitation in the torsional motion is more weakened, even closed to normal level. Then by the device, it has not been strengthened evidently in the torsional rotation which the stability of the unit. The device is necessarily with the auxiliary fixation by the pedicle screws. In summary, various design requests, such as the structure, the material, the mechanical function, biological mechanics, and so on, have been attained by the designed minimally invasive lumbosacral fusion and fixation device via presacral approach fit to the native, which is one kind reasonable, feasible and optimized minimally invasive operative system for the anterior axial lumbosacral fusion and fixation. At the same time, we may through other research correlated and the experimental clinical practice to further improve and consummate it, which is finally applied in the clinical treatment smoothly.
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