Biomechanical effects of posterior lumbar interbody fusion with vertical placement of pedicle screws compared to traditional placement

BACKGROUND The pedicle screw technique is widely employed for vertebral body fixation in the treatment of spinal disorders.However,traditional screw placement methods require the dissection of paraspinal muscles and the insertion of pedicle screws at specific transverse section angles(TSA).Larger TSA angles require more force to pull the muscle tissue,which can increase the risk of surgical trauma and ischemic injury to the lumbar muscles.AIM To study the feasibility of zero-degree TSA vertical pedicle screw technique in the lumbosacral segment.METHODS Finite element models of vertebral bodies and pedicle screw-rod systems were established for the L4-S1 spinal segments.A standard axial load of 500 N and a rotational torque of 10 N/m were applied.Simulated screw pull-out experiment was conducted to observe pedicle screw resistance to pull-out,maximum stress,load-displacement ratio,maximum stress in vertebral bodies,load-displacement ratio in vertebral bodies,and the stress distribution in pedicle screws and vertebral bodies.Differences between the 0-degree and 17-degree TSA were compared.RESULTS At 0-degree TSA,the screw pull-out force decreased by 11.35%compared to that at 17-degree TSA(P<0.05).At 0-degree and 17-degree TSA,the stress range in the screw-rod system was 335.1-657.5 MPa and 242.8-648.5 MPa,separately,which were below the fracture threshold for the screw-rod system(924 MPa).At 0-degree and 17-degree TSA,the stress range in the vertebral bodies was 68.45-78.91 MPa and 39.08-72.73 MPa,separately,which were below the typical bone yield stress range for vertebral bodies(110-125 MPa).At 0-degree TSA,the load-displacement ratio for the vertebral bodies and pedicle screws was slightly lower compared to that at 17-degree TSA,indicating slightly lower stability(P<0.05).CONCLUSION The safety and stability of 0-degree TSA are slightly lower,but the risks of screw-rod system fracture,vertebral body fracture,and rupture are within acceptable limits.

TOPOLOGY AND VORTEX STRUCTURES OF A CURVING TURBINE CASCADE WITH TIP CLEARANCE (Ⅱ)- TOPOLOGICAL FLOW PATTERN AND VORTEX STRUCTURE IN THE TRANSVERSE SECTION OF A BLADE CASCADE

By means of ink trace visualization of the flows in conventional straight, positively curved and negatively curved cascades with tip clearance, and measurement of the aerodynamic parameters in transverse section, and by appling topology theory, the topological structures and vortex structure in the transverse section of a blade cascade were analyzed. Compared with conventional straight cascade, blade positive curving eliminates the separation line of the upper passage vortex, and leads the secondary vortex to change from close separation to open separation, while blade negative curving effects merely the positions of singular points and the intensities and scales of vortex.

Foot transverse arch instability following sequential ligament sectioning and screw reconstruction

Objectives: To investigate foot transverse arch biomechanical stability contributed by the second metatarsal and the three ligaments connecting medial cuneiform to the second metatarsal base.Methods: Six fresh-frozen cadaveric lower extremities were dissected to expose the

Cambial Variants in the Family Menispermaceae in Taiwan

Anatomical data regarding the climbing modes and cambial variants of the stem transverse section in the Menispermaceae in Taiwan are lacking. Here, we examined the climbing modes and anomalous structure of climber stems in this family. Reviewing the previous reports of cambial variants in angiosperm liana families, a list of angiosperm liana families processing specified types of cambial variants and the terms based on description for the transverse section of a stem were provided. The results show that Cocculus laurifolius DC. is a shrub, Stephania cephalantha Hayata and Stephania longa Lour. are vines, and the remaining 13 species are lianas. In all species, the climbing mode was twining and dextrorse stems. The anomalous structure of the stem comprised successive cambia in Cocculus laurifolius, a combination of xylem in plates and dissected xylem in Cocculus orbiculatus (L.) DC., and xylem in plates in the remaining 14 species. In the genus Cyclea, parenchyma proliferation from the secondary xylem resulted in the development of 1 - 3 linear lobes in each collateral vascular bundle. The vessel diameter of C. laurifolius is <50 μm which is the smallest size due to shrub in its life stage. C. orbiculatus had the longest collateral vascular bundles, longest rays and widest rays. Cyclea ochiaiana (Yamam.) S. F. Huang & T. C. Huang had the widest collateral vascular bundles. Sinomenium acutum (Thunb.) Rehder & E. H. Wilson had the highest vessel density. Tinospora crispa (L.) Hook. F. et Thoms develops blunt tubercles on the epidermis and Stephania tetrandra S. Moore bears conspicuous phellem layer. Those findings, such as the climbing mode, the features of parenchyma proliferation, the features of collateral vascular bundles (number, width, length), dimorphic vessels, and size and density of vessels, highlight new anatomical characteristics for species identification in the Menispermaceae in Taiwan.