Entry Trajectory Research Articles

The Optimal Entry Point and Trajectory for Pedicle Screws to Avoid Superior Facet Joint Violation and Pedicle Penetration.

Background Accuracy is crucial in surgeries involving pedicle screws. This study aimed to determine the optimal screw entry points and trajectory angles for the pedicle screw technique used in the surgical treatment of lumbar instability. Methods To achieve this goal, a comparison was made between the screw entry points and trajectories determined using the commonly used intersection technique and those created in a three-dimensional (3D) simulation environment. Thirty-two cases of lumbar degenerative spondylolisthesis, selected from surgeries between 2018 and 2023, were included. Preoperative lumbar computed tomography (CT) images were converted into 3D models, and simulations for pedicle screw placement were conducted. Results Using the intersection technique, upper facet damage was noted in 31.3% of L1, 37.5% of L2, 6.3% of L3, and 31.3% of L5 segments. Adjustments to entry points and angles in the 3D environment were made to determine optimal trajectories. The revised screw angles showed statistically significant improvements at L1, L2, and L5 segments compared to the intersection technique. Conclusions The intersection technique does not appear safe in preserving the superior facet joint. A more lateral and caudal pedicle entry should be preferred in the upper segments, and at L5, a more lateral pedicle entry should be used. Consequently, the screw angles should be adjusted accordingly.

Entry trajectory optimization of lifting-body vehicle by successive difference-of-convex programming

The complexity of the three-dimensional entry trajectory optimization problem has escalated due to the need to liberalize the angle of attack and bank angle as control variables, thereby enhancing the inherent maneuverability and control capabilities of lifting-body vehicles. The difference-of-convex (DC) properties inherent in the constraints of the problem are exploited in this paper. A DC decomposition approach is utilized to address the nonlinear auxiliary control equations, and the DC relaxation technique is applied to resolve iteration infeasibilities arising from Taylor expansion. The dependence on the initial trajectory is diminished by the implementation of an exact penalty method, thus improving the applicability of the methods. Furthermore, a control variable oscillation suppression mechanism has been constructed to tackle the control variable oscillation issues arising from the relaxation of the angle of attack and bank angle. This mechanism effectively suppresses large jumps in the angle of attack and high-frequency oscillations in the bank angle. Two novel successive DC programming methods are proposed: the successive concave-convex procedure and the successive proximal bundle method, functioning independently of trust-region constraints. Numerical experiments have demonstrated that the two proposed successive DC optimization methods exhibit exceptional performance in accuracy, feasibility, adaptability, and low sensitivity to initial values when applied to solving the three-dimensional entry trajectory optimization problem.

Aerothermal Loads on a Representative Porous Mesostructure at Flight Conditions Using Direct Simulation Monte Carlo

Spacecraft require thermal protection systems (TPS) in order to survive the extreme conditions present during atmospheric entry missions. Porous ablators are a class of TPS materials that have been used successfully on several entry missions, although they can be difficult to model because of their complex nature at the micro- and mesoscales. Specifically, the processes that lead to mechanical erosion (spallation) of these materials are poorly understood. In order to gain insight into the spallation process, the current work computes aerothermal loads on a mesostructure representative of FiberForm (the substrate of phenolic impregnated carbon ablator) by leveraging a simulation framework involving loosely coupled Computational Fluid Dynamics-Direct Simulation Monte Carlo (CFD-DSMC) simulations of hypersonic boundary layers. CFD boundary layers are extracted from two altitudes, 68.9 and 81 km, along the Stardust entry trajectory and are imposed as boundary conditions on a DSMC simulation over an artificially generated mesostructure, which is representative of the charred layer of the TPS material. In order to produce high-quality results, the DSMC boundary conditions require careful consideration; specifically, Chapman–Enskog distributions are needed to account for large velocity and temperature gradients. Visualizations of the DSMC flowfield indicate excellent agreement with the original CFD data, and the aerothermal loads (heat flux and traction force) on the surface were examined using probability density functions. Additionally, the effects of pyrolysis blowing through the mesostructure on the surface properties are also determined.

Augmented reality–assisted intraoperative navigation increases precision of glenoid inclination in reverse shoulder arthroplasty

BackgroundReverse Total Shoulder Arthroplasty (RTSA) is the standard of care for patients with glenohumeral osteoarthritis and rotator cuff deficiency. Preoperative RTSA planning based on medical images and patient-specific instruments has been established over the last decade. This study aims to determine the effects of using augmented reality assisted intraoperative navigation (ARIN) for baseplate positioning in RTSA compared to preoperative planning. It is hypothesized that ARIN will decrease deviation between preoperative planning and postoperative baseplate positioning. Moreover, ARIN will decrease deviation between the (senior) more (> 50 RTSA/year) and less experienced (junior) surgeon (5-10 RTSA/year). MethodsPreoperative CT scans of sixteen fresh-frozen cadaveric shoulders were obtained. Baseplate placements were planned using a validated software. The data was then converted and uploaded to the augmented reality system (NextAR; Medacta International, Castel San Pietro, Switzerland). Each of the eight RTSAs were implanted by a senior and a junior surgeon, with four RTSAs utilizing ARIN and four without. A postoperative CT scan was performed in all cases. The scanned scapulae were segmented, and the preoperative scan was laid over the postoperative scapula by nearest iterative point cloud analysis. The deviation from the planned entry point and trajectory was calculated regarding the inclination, retroversion, medialization (reaming depth)/lateralization, antero-posterior position and superior/inferior position of the baseplate. Data are reported as mean ± standard deviation (SD) or mean and 95% confidence interval (CI). P values <0.05 were considered statistically significant. ResultsThe use of ARIN yielded a reduction in the absolute difference between planned and obtained inclination from 9° (SD: 4°) to 3° (SD°:2) (p=0.011). Mean difference in planned-obtained inclination between surgeons was 3° in free-hand surgeries (95%CI: -4,10, p=0.578), while this difference reduced to 1° (95%CI: -6, 7, p=0.996) using ARIN. Retroversion, medialization (reaming depth)/lateralization, antero-posterior position and superior/inferior position of the baseplate were not affected by using ARIN. Surgical duration was increased using ARIN for both the senior (10 mins) and junior (18 mins) surgeon. ConclusionsThe implementation of augmented reality assisted intraoperative navigation (ARIN) leads to greater accuracy of glenoid component placement, specifically with respect to inclination. Further studies have to verify if this increased accuracy is clinical important. Furthermore, ARIN allows less experienced surgeons to achieve a similar level of accuracy in component placement comparable to more experienced surgeons. However, the potential advantages of ARIN in RTSA are counterbalanced by an increase in operative time.

Rapid and Near-Analytical Planning Method for Entry Trajectory under Time and Full-State Constraints

A rapid trajectory-planning method based on an analytical predictor–corrector design of drag acceleration profile and a bank-reversal logic based on double-stage adaptive adjustment is proposed to solve the entry issue under time and full-state constraints. First, an analytical predictor–corrector algorithm is used to design the profile parameters to satisfy the terminal of altitude, velocity, range, time, and flight-path angle constraints. Subsequently, an adaptive lateral planning algorithm based on heading adjustment and maintenance is proposed to achieve the flight stage adaptive division and determination of the bank-reversal point, thereby satisfying the terminal position and heading angle constraints. Concurrently, a rapid quantification method is proposed for the adjustable capacity boundary of the terminal heading angle. On this basis, a range-and-time correction strategy is designed to achieve high precision and the rapid generation of a three-degree-of-freedom entry trajectory under large-scale lateral maneuvering. The simulation results demonstrated that compared with the existing methods, the proposed method can adaptively divide flight stages, ensuring better multitask applicability and higher computational efficiency.

Endoscopic Endonasal Occipitocervical Fixation with a Customized Three-Dimensional Printed Titanium Plate-Screw Construct: A Cadaveric Feasibility Study

To evaluate the feasibility of a novel method for occipitocervical fixation (OCF) through the endonasal corridor. Thin-cut computed tomography scans were obtained for 5 cadaveric specimens. Image segmentation was used to reconstruct 3D models of each O-C1 joint complex. Using computer-aided design software, plates were custom-designed to span each O-C1 joint, sit flush onto the bony surface, and accommodate screws. The final models were 3D-printed in titanium. For implantation, specimens were held in pin-fixation and registered to neuronavigation. A rigid 0º endoscope was used for endonasal visualization. An inverted U-shaped nasopharyngeal flap was raised to expose the occipital condyles and C1. The plates were introduced and fixed with bone screws. Computed tomography scans were obtained to assess screw accuracy and proximity to critical neurovascular structures. Screw entry points and trajectories were recorded. Endonasal OCF was performed on 5 cadaveric specimens. The mean starting point for occipital condyle screws was 6.17 mm lateral and 5.38 mm rostral to the medial O-C1 joint. Mean axial and sagittal trajectories were 7.98° and 6.71°, respectively. The mean starting point for C1 screws was 16.11 mm lateral to the C1 anterior tubercle and 6.39 mm caudal to the medial O-C1 joint. Mean axial and sagittal trajectories were 10.97° and-9.91°, respectively. Endonasal OCF is technically and anatomically feasible. The application of this technique may allow for same-stage endonasal decompression and fixation, offering a minimally invasive alternative to current methods of fixation and advancing surgeons' ability to treat pathology of the craniovertebral junction. Next steps will focus on biomechanical testing.

Comparison of the Accuracy and Efficiency of Two Dynamic Navigation System Workflow for Fiber-post Removal: Small versus Large Field-of-view Registration Workflows

IntroductionThis study investigates the feasibility of a dynamic navigation system (DNS) small field of view workflow (DNS-SFOVw) for fiber-post removal and compares its accuracy and efficiency to the conventional large field of view workflow (DNS-LFOVw). MethodsFifty-six extracted human maxillary molars were divided into DNS-SFOVw (n = 28) and DNS-LFOVw (n = 28). The palatal canal was restored with an intraradicular RelyX fiber post and luted with RelyX Unicem; a core buildup was used. Teeth were mounted in a 3D-printed surgical jaw. A preoperative cone-beam computed tomography (CBCT) scan was taken with a 40 × 40 mm FOV for the DNS-SFOVw and a single arch CBCT scan for the DNS-LFOVw. The drilling entry point, trajectory, angle, and depth were planned in the X-guide software. The DNS registration method for the DNS-SFOVw was virtual-based registration on teeth, and the marker point-based method was used for the DNS-LFOVw. The fiber posts were drilled out under DNS guidance. A postoperative CBCT scan was taken. Three-dimensional deviations, angular deflection, number of mishaps, registration, and total operation time were calculated. ResultsThe DNS-SFOVw was as accurate as DNS-LFOVw (P > .05). The DNS-LFOVw registration time was less than DNS-SFOVw (P < .05). There was no difference in the number of mishaps (P > .05). Both DNS-SFOVw and DNS-LFOVw were time-efficient, with DNS-LFOVw taking less total operational time (P < .05). ConclusionWithin the limitations of this in-vitro study, the DNS-SFOVw was as accurate as the DNS-LFOVw for fiberpost removal. Both DNS-LFOVw and DNS-SFOVw were time-efficient in removing fiber-posts.

Improved sequential convex programming based on pseudospectral discretization for entry trajectory optimization

Sequential convex programming (SCP) is widely used to solve entry trajectory optimization problems. However, challenges persist in scenarios with strict constraints, such as unsolvable convex subproblems, iterative solution oscillations, and slow convergence rates. This study introduces an enhanced SCP algorithm designed to address these limitations. First, hp Radau pseudospectral discretization is used instead of trapezoidal discretization to improve the efficiency in solving subproblems while maintaining discretization accuracy. Second, the trust region is adaptively updated on the basis of trajectory information during iterations. Additionally, constraint relaxation and virtual control are introduced to facilitate smooth iteration at the initial stage. The regularization technique is also utilized to improve the convergence rates. Finally, the proposed algorithm is validated through two examples: maximum-terminal-velocity entry and maximum-terminal-longitude entry. The results show that these two problems cannot be effectively solved using the basic SCP algorithm. However, the proposed algorithm, along with the trust-region SCP algorithm and GPOPS, can solve them efficiently. With comparable accuracy in the obtained solutions, the algorithm proposed in this paper requires only half the CPU time of the trust-region SCP algorithm and just 5 % of the computing time of the general-purpose open-source solver GPOPS.

Enhancing intersection safety in autonomous traffic: A grid-based approach with risk quantification

Existing studies on autonomous intersection management (AIM) primarily focus on traffic efficiency, often overlooking the overall intersection safety, where conflict separation is simplified and traffic conflicts are inadequately assessed. In this paper, we introduce a calculation method for the grid-based Post Encroachment Time (PET) and the total kinetic energy change before and after collisions. The improved grid-based PET metric provides a more accurate estimation of collision probability, and the total kinetic energy change serves as a precise measure of collision severity. Consequently, we establish the Grid-Based Conflict Index (GBCI) to systematically quantify collision risks between vehicles at an autonomous intersection. Then, we propose a traffic-safety-based AIM model aimed at minimizing the weighted sum of total delay and conflict risk at the intersection. This entails the optimization of entry time and trajectory for each vehicle within the intersection, achieving traffic control that prioritizes overall intersection safety. Our results demonstrate that GBCI effectively assesses conflict risks within the intersection, and the proposed AIM model significantly reduces conflict risks between vehicles and enhances traffic safety while ensuring intersection efficiency.

A novel transcoronal surgical technique for the treatment of cystic lesions of the distal phalanx: A cadaveric study.

To assess the feasibility of a novel transcoronal approach for the treatment of axial type 3 cysts of the palmar/plantar aspect of the distal phalanx (P3). Ex vivo, experimental study. Ten cadaveric specimens, four forelimbs and six hindlimbs. All cadaveric specimens underwent radiographically guided drilling, followed by cortical screw placement. The cartilage was macroscopically assessed after disarticulation of the distal interphalangeal joint. The entry point and trajectory were evaluated with computed tomography. Results were categorized as: axial, near-axial and abaxial. The minimal distance from the outer margin of the drill hole and the proximal border of the subchondral bone plate was measured using frontal computed tomographic slices. Eight of the 10 screws were in an axial to near-axial position and nine followed the desired axial to near-axial trajectory. One screw was inserted axially but continued in an abaxial trajectory. Iatrogenic damage to the joint cartilage, flexor cortex and solar canal of P3 was not observed. All cortical screws were placed close to the proximal subchondral bone-plate of P3. The desired axial/near-axial drilling and screw placement, under radiographic guidance, was achieved in nine out of 10 specimens. This novel technique seems promising for the treatment of inaccessible P3 cysts. Additional studies are required to investigate its feasibility in clinical cases, and the long-term outcome following transcystic screw placement of type 3 P3 cysts.

Study on Water Entry of a 3D Torpedo Based on the Improved Smoothed Particle Hydrodynamics Method

The water entry of a torpedo is a complex nonlinear problem, involving transient impact, free surface deformation, droplet splashing, and fluid–structure coupling, which poses severe challenges to traditional mesh methods. The meshless smoothed particle hydrodynamics (SPH) method shows unique advantages in capturing the complex features of the water entry of the torpedo at different entry angles. However, it still suffers from some inherent shortcomings, such as low surface discretization accuracy, poor discretization flexibility, and low calculation efficiency. In this study, an improved adaptive SPH algorithm is proposed to investigate the water entry of the torpedo accurately and efficiently. This method integrates meshless point generation and adaptive techniques simultaneously. The numerical results demonstrate that when the torpedo vertically enters the water at different velocities, the induced impact loads acting on the head of the torpedo fluctuate significantly with two peak values in the initial stage and thereafter stabilize in a later stage. The impact load acting on the torpedo, the entry depth of the torpedo, the splash height of the droplets, and the size of the cavity generated around the torpedo increase with the increment in the entry velocity. When the torpedo enters the water at different entry angles under the same initial entry velocity, both the vertical and the horizontal movements of the torpedo are observed, which results in more complex variations in parameters along the x- and y-axes. The findings and the corresponding numerical method in this study can provide a certain basis for the future designs of the entry trajectory and the structural bearing capacity of torpedoes.

Commissioning of Upgrades to T6 to Study Giant Planet Entry

The scientific potential of a mission to the ice giants is well recognized and has been identified by NASA and ESA as a high priority on several occasions, most recently in the 2023–2032 Decadal Survey. The payload capacity of such a spacecraft is limited by the heat shield thickness, which must be sized conservatively due to a lack of reliable data for convective and radiative heat flux along the proposed entry trajectories. Major upgrades to the Oxford T6 Stalker Tunnel have been commissioned that allow study of giant planet entry trajectories, including a flammable gas handling system, a Mach 10 expansion nozzle, and a steel shock tube with optical access. Initial testing has been completed in shock tube and expansion tunnel modes, with peak shock speeds of 18.9 km/s achieved. Convective heat flux and surface pressure were measured at several locations on a 45° sphere cone model in expansion tunnel mode. Measurements of the radiating shock layer were made in shock tube mode to assess the effect of CH4 concentration. This work establishes the first high-enthalpy giant planet entry test bed in Europe.

Neural Tract Avoidance Path-Planning Optimization: Robotic Neurosurgery

Background: We propose a three-dimensional path-planning method to generate optimized surgical trajectories for steering flexible needles along curved paths while avoiding critical tracts in the context of surgical glioma resection. Methods: Our approach is based on an application of the rapidly exploring random tree algorithm for multi-trajectory generation and optimization, with a cost function that evaluates different entry points and uses the information of MRI images as segmented binary maps to compute a safety trajectory. As a novelty, an avoidance module of the critical neuronal tracts defined by the neurosurgeon is included in the optimization process. The proposed strategy was simulated in real-case 3D environments to reach a glioma and bypass the tracts of the forceps minor from the corpus callosum. Results: A formalism is presented that allows for the evaluation of different entry points and trajectories and the avoidance of selected critical tracts for the definition of new neurosurgical approaches. This methodology can be used for different clinical cases, allowing the constraints to be extended to the trajectory generator. We present a clinical case of glioma at the base of the skull and access it from the upper area while avoiding the minor forceps tracts. Conclusions: This path-planning method offers alternative curved paths with which to reach targets using flexible tools. The method potentially leads to safer paths, as it permits the definition of groups of critical tracts to be avoided and the use of segmented binary maps from the MRI images to generate new surgical approaches.

Numerical investigation on the effect of feed operating parameters and inlet structure on a cyclone utilizing flow splitting for performance enhancement

The shunting technique is regarded as one of the most crucial approaches for suppressing localized secondary flow within a cyclone. This study employs the Reynolds stress model and discrete phase model to investigate the impact of inlet structure and feed operating parameters on the performance of enhanced cyclone with split flow (ECSF), aiming to further enhance its efficiency. The findings demonstrate that the optimum feed velocity of ECSF is 29 m/s, which surpasses that of Lapple cyclone at 23 m/s. In addition, both a contracting inlet and multiple inlets contribute to enhancing the separation efficiency of ECSF. Specifically, ECSF with a contracting inlet exhibits a total separation efficiency of 86.8% for 2.5 μm particles, representing an improvement of 12.3% compared to ECSF with a straight inlet configuration. The enhancement in separation efficiency achieved through the implementation of the four-inlet design is even more pronounced. The segregated particles are directed into the discharge pipe via either underflow or bypass flow, and the trajectory of particle entry into the discharge pipe is closely associated with their cross-sectional positioning prior to entering the cylinder.

The influence of heterogeneous catalytic processes on the heat flux to the surface and the chemical composition of the shock layer at high-speed flow around blunt bodies

Numerical modeling of the high-speed flow of a multicomponent dissociated gas around a blunt body was carried out for the flow regime corresponding to the thermally stressed point of the gliding trajectory of entry into the Earth's atmosphere in the surface temperature range of 800–2000 K. As boundary conditions, a stage-by-stage model of heterogeneous catalysis of the interaction of dissociated air with the thermal protection material SiO2 was used, previously developed by the authors on the basis of transition state theory and quantum mechanical calculations. The dependence of the modes of heterogeneous chemical reactions on the surface temperature and the density of surface adsorption centers and their influence on the chemical composition of the shock layer and the convective heat flux to the streamlined surface are analyzed. The contributions of individual mechanisms of heterogeneous recombination to the total rate of formation of molecules on the surface are estimated. The possibility of using the density of adsorption sites as an effective parameter when setting boundary conditions on a real thermal protection surface in flow problems is shown.

Research into the anatomy of the subaxial cervical pedicle for ensuring screw insertion safety.

The study aimed to determine the optimal entry points and trajectories for posterior subaxial cervical pedicle screw (CPS) fixation. Computed tomography (CT) and Mimics software were used to evaluate the subaxial cervical pedicle in 42 cervical spine CT scans. The width of the cervical pedicle was measured and compared at medial angulations of 30°, 35°, 40°, 45°, 50°, 55°, and 60° relative to the midline sagittal plane. Based on an observational examination of the positions of all cervical 3-dimensional models and screws, the proposed entry point for C3-7 CPS was analyzed. Although the variations in C3-6 pedicle width (PW) among 45°, 50°, and 55° were not statistically significant, they were significantly larger than the differences among 30°, 35°, 40°, and 60° angles (P < .05). The differences in C7 PW between the 30°, 35°, 40°, and 45° angles were not statistically different even though the 30°, 35°, 40°, and 45° angles were significantly bigger. (P < .05). The proposed entry point for C3-7 CPS was below the junction of the lateral and lower borders of the superior articular process joint surface. The entry point for C3-7 levels was below the junction of the lateral and lower borders of the superior articular process joint surface. The optimal medial angulation for the posterior C3-6 CPS was 45°-55° and that for the posterior C7 CPS was 30°-45°. The sagittal angle of the posterior C3-7 CPS was parallel to the corresponding upper endplate.

Vertical water entry of a cylinder considering wind and linearly sheared flow effect: A numerical investigation

Objects entering water is a complex multiphase flow event that exhibits nonlinear and transient characteristics. This study examines the impact cavities, multiphase flow characteristics, and motion behaviors of a cylinder during vertical water entry, considering different flow and entry velocities. A three-dimensional model was carried out using OpenFOAM® framework, taking into account the effects of wind and linearly sheared flow through newly customized initial and boundary conditions. The overset mesh technique was applied to capture the water entry trajectories of the moving cylinder. Numerical results for the cavity evolution and cylinder motion behaviors were validated against published laboratory tests. The cavity closure patterns were classified into four categories based on the evolution characteristics, which were found to be more complex than those observed under calm water and uniform current conditions. Furthermore, the rapid closure of the splash dome results in a unique cavity flow phenomenon, which creates a suction air channel. The velocities of the flow and water entry have a noticeable impact on the closure modes and time of the cavity. This, accordingly, affects the motion characteristics of the cylinder, as well as the evolution of the velocity field, pressure field, and vortex structures.

АНАЛИЗ ВЛИЯНИЯ КОНСТРУКТИВНЫХ ПАРАМЕТРОВ НА МАНЕВРЕННОСТЬ ТРАКТОРА СО ВСЕМИ УПРАВЛЯЕМЫМИ КОЛЕСАМИ

The results of a theoretical analysis are presented to assess the influence of the longitudinal base and track of a tractor with all steerable wheels on its basic geometric and kinematic characteristics in curved motion, characterizing its maneuverability. The maximum abscissa and ordinate of the trajectory of the entrance to the turn and the minimum theoretical radius of the steady-state stage of a circular loop-free turn are taken as estimated indicators. A comparison is given with the calculation results obtained in the study of a tractor with front steerable wheels under identical design parameters and operating conditions. To determine the necessary desired parameters describing the trajectory of the curved movement of the tractor, parametric equations are obtained. Analysis of the calculation results showed that with an alternate increase in the length of the longitudinal base from 2.2 m to 3.0 m and the track width from 1.2 m to 2.2 m, with the remaining unchanged design and operational characteristics, the minimum radius increases, respectively, by 18.5% and 16.3%, and the maximum ordinate of the trajectory of entry into the turn – by 3.9% and 16.6 %, while the maximum abscissa of this section of the trajectory decreases by 20.4 % and 40.4%. A comparison of the turning method, which is the subject of research in this paper, with the method of turning the front steerable wheels, all other things being equal, showed the effectiveness of the first of them. An increase in the maximum abscissa by 1.75 times was revealed, but a decrease in the maximum ordinate by 1.05 times and the minimum turning radius by 1.69 times. This gives reason to talk about the best maneuverability of a tractor with all steerable wheels.

Intraoperative lateral wall breach simulation in the cadaveric spine and the impact of thread designs of screws on pullout strength in the osteoporotic thoracic vertebrae: A biomechanical study in human cadavers.

This study aimed (1) to simulate pedicle screw pullout after intraoperative external wall perforation and (2) to assess restoration strength with different thread designs in the pedicle screw instrumentation for osteoporotic thoracic vertebrae. Twenty fresh-frozen human cadaveric thoracic vertebra bodies were prepared and divided into 4 groups: group 1, 5.5 mm × 45 mm polyaxial single thread pedicle screws (PASTS); group 2, after wall injury 5.5 mm × 45 mm PASTS; group 3, 6.5 mm × 45 mm PASTS after wall injury; and group 4: 6.5 mm × 45 mm polyaxial mixed-threaded screws after wall injury. While group 1 was the control group, groups 2, 3, and 4 were used as study groups after the lateral wall breach. All prepared screw units were placed on a universal pullout measurement testing device. The mean bone mineral density for 20 thoracic vertebrae was 0.57 ± 0.12 g/cm2 (range 0.53-0.6 g/cm2 ). The mean pullout strength was 474.90 Newtons (N) for group 1, 412.85 N for group 2, 475.4 N for group 3, and 630.74N for group 4. The lateral wall breach caused a 14.1 % decrease in average pullout strength compared with the initial screw pullout. Mixed (double)-threaded screws increased pullout strength compared to 6.5 mm screws (P=.036) Conclusion: Using a 1 mm thicker polyaxial pedicle screw or mixed (double)-threaded pedicle screw seems to increase pullout strength; however, this was statistically significant only for group 4. In the thoracic spine, the redirection possibility of the pedicle screw is limited, and augmentation with cement will not be appropriate due to the risk of wall injury-related leakage. Therefore, care should be taken to avoid violating the lateral cortex by using appropriate pedicle entry points and trajectories.

Reduced-Order Desensitized Optimal Control for Mars Entry Trajectory Optimization

Reduced-Order Desensitized Optimal Control for Mars Entry Trajectory Optimization