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The study of spine biomechanics is an important foundation for understanding spine function, spine pathogenesis as well as selection of spinal therapeutic approaches. This review summarizes the basic research progress and results of spine biomechanics from five aspects, including the individual components of spine (such as spinal vertebrae), intervertebral discs, ligaments and functional spinal units and the whole spine. All these studies include the in vitro and in vivo experiments on human spinal specimens and animal spinal specimens, and the results of different research methods such as the mathematical model. This review also summarizes some of the poorly understood biomechanical data, which would become an important research direction in the future.
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Objective To simulate the tightening procedure of a cancellous lag screw by using the implicit dynamic analysis method, and to evaluate the stress distributions on the screw-bone interface. Methods Finite element models of a lag screw with the surrounding bone were developed, and the implicit solver was set up for implicit dynamic analysis on the tightening procedure of the lag screw. The mechanical properties of the screw-bone interface were also analyzed according to strain and stress distributions on the screw and the surrounding bone. Results The stress of the lag screw was mainly distributed in the proximal portion of the screw thread rod. The high-stress region of the bone around the screw was located outside the outer edge of the screw, and it was approximately equal to the depth of the thread. The area of high-stress distributions on the bone was the main region that resisted screw stripping. Conclusions The method of implicit dynamic analysis can accurately simulate the mechanical properties of the screw-bone interface during screw tightening. The discovery of high-stress distributions on the surrounding bone can help researchers to further understand and improve the stability of screw insertion.
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BACKGROUND:The aim of spinal mobilization and spinal manipulation is to correct vertebral subluxation. However, facet joint pressures are not clear during these two therapies. OBJECTIVE:To compare human lumbar facet joint pressures during simulated high-velocity, low-amplitude spinal manipulationversuslow-velocity, low-amplitude spinal mobilization. METHODS:Totaly 12 adult fresh lumbar spinal specimens (T12-S2) were divided into two groups randomly. Parameters of simulated spinal mobilization (n=6): preload angle 15° (speed 3°/s), maximum angle 20° (speed 1°/s), with 9 N horizontal force to L5 spinous process. Parameters of simulated spinal manipulation (n=6): preload angle 15° (speed 3°/s), impulse angle 20° (impulse speed 33°/s), with 22 N horizontal force to L5 spinous process. Pressures of bilateral L4-5/L5-S1 facet joints were measured with Tekscan system. RESULTS AND CONCLUSION:(1) During two spinal manipulative therapies (rotation to the right and then back to the neutral position), pressures of right facet joints decreased first and then increased gradualy, while pressures of left facet joints changed oppositely. (2) Pressures of right facet joints were similar regardless of manipulation type (P > 0.05). The maximum pressure of left facet joints was larger during manipulation than that during mobilization (P 0.05). Both ascending and descending speeds of the left facet joints were larger during manipulation than that during mobilization (P < 0.01). (4) During two spinal manipulative therapies, pressures of ipsilateral facet joints decreased first and then increased, while pressures of contralateral facet joints increased first and then decreased. Joint pressure after treatment restored to that before treatment. (5) Impulse speed and magnitude of pressures of facet joints during manipulation were larger than that during mobilization. Facet joints are more possible to be injured during manipulation than that during mobilization. During manipulation, we should pay attention to the speed and intensity of the impact.
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OBJECTIVE:To compare the physical chemistry properties of copying(A) and original(B) aluminium phosphate gel METHODS:We examined the character,antacid activity,isolating capacity against H+ ions and viscosity in different pH values of two products RESULTS:Product A was not better than product B in the Character,antacid activity,isolating capacity against H+ ions and viscosity;The antacid activity of two preparations not influenced obviously by the food with low concentration;Two preparations all had difference physical chemistry properties in batches CONCLUSION:Product B was better than A in comparison of the physical chemistry properties