Screw Design Research Articles

Reduction quality in lateral view of X-ray and hypoalbuminemia are associated with postoperative mortality in elderly pertrochanteric fracture patients.

Pertrochanteric fracture is one of the most prevalent public health issues across the world for the elderly population. The purpose of this study was to investigate the association between surgical factors and postoperative mortality in patients with intramedullary nail-treated pertrochanteric fractures. A retrospective cohort study was designed to evaluate the pertrochanteric fracture patients treated with intramedullary nail between January 2016 to February 2021. The surgical factors included the Dorr morphology, Arbeitsgemeinschaft für Osteosynthesefragen/Orthopedic Trauma Association (AO/OTA) classification of fractures, the tip-apex distance (TAD), location of the cephalic screw, reduction quality in anterior-posterior (AP) and lateral views, the integrity of the lateral wall, and the design of cephalic screws. Using univariate and multivariate Cox proportional hazard models, the association between these risk factors and postoperative mortality in patients with this type of fractures was evaluated. A total of 169 pertrochanteric fracture patients treated with intramedullary nails were included in our study, with the average age of 82.68±5.93 years. The mortality rates at 3 months, 1 year, and the end of follow-up were 4.14%, 11.24%, and 26.04%, respectively. According to the univariate Cox analysis, age, gender, preoperative levels of hemoglobin (Hb) and albumin (Alb) were associated with a poor overall survival (OS) (P<0.05). After multivariate adjustment, the pre-operative level of Alb (P<0.001) and the reduction in lateral view (P<0.001) were shown to be independent risk factors for poor OS. The preoperative hypoalbuminemia and reduction quality in lateral view were associated with postoperative mortality in our study. Therefore, optimizing both parameters could improve the prognosis in elderly pertrochanteric fracture patients.

Optimal Insertion Torque for Orthodontic Anchoring Screw Placement: A Comprehensive Review

The optimal insertion torque (IT) for orthodontic anchoring screws (OASs) was hypothesized to vary with OAS features and insertion methods. This review examines the indexed English literature, to determine the appropriate IT range for OAS success based on area of insertion and OAS features. Eleven original articles with OAS placement in humans including IT and success rate were selected and were used to evaluate the relationships among IT, success rates, screw design, and placement methods at different sites. The ITs and success rates ranged from 6.0 ± 3.2 to 15.7 ± 2.3 Ncm and from 62.5 to 100.0% in the upper and lower buccal alveolar areas, respectively. For the mid-palatal area, the range was 14.5 ± 1.6 to 25.6 ± 5.5 Ncm and 83.0 to 100.0%, respectively. ITs of 5–12 and 6–14 Ncm were found to be optimal for the commonly used φ1.5–1.7 mm OASs in the upper and lower interproximal areas, respectively. In the mid-palatal suture area, ITs of 11–16 and 20–25 Ncm were considered suitable for tapered φ1.5 mm and φ2.0 mm OASs, respectively. Although identified optimal IT ranges deserve the recommendations, care must be taken to monitor the IT during placement constantly.

Additively manufactured medical bone screws: an initial study to investigate the impact of lattice-based Voronoi structure on implant primary stability

PurposeThe present study investigates the mechanical properties of three types of Ti6Al4V ELI bone screws realized using the laser powder bed fusion (LPBF) process: a fully threaded screw and two groups containing differently arranged sectors made of lattice-based Voronoi (LBV) structure in a longitudinal and transversal position, respectively. This study aims to explore the potentialities related to the introduction of LBV structure and assess its impact on the implant’s primary stability and mechanical performance.Design/methodology/approachThe optimized bone screw designs were realized using the LPBF process. The quality and integrity of the specimens were assessed by scanning electron microscopy and micro-computed tomography. Primary stability was experimentally verified by the insertion and removal of the screws in standard polyurethane foam blocks. Finally, torsional tests were carried out to compare and assess the mechanical strength of the different designs.FindingsThe introduction of the LBV structure decreases the elastic modulus of the implant. Longitudinal LBV type screws demonstrated the lowest insertion torque (associated with lower bone damage) while still displaying promising torsional strength and removal force compared with full-thread screws. The use of LBV structure can promote improved functional performances with respect to the reference thread, enabling the use of lattice structures in the biomedical sector.Originality/valueThe paper fulfils an identified interest in designing customized implants with improved primary stability and promising features for secondary stability.

The relationship of peri-implant soft tissue wound healing with implant cover screw design: Cross-sectional study.

Dental implants are frequently preferred method for oral rehabilitation all over the world. The incidence of various complications such as incorrect prosthesis, peri-implant mucositis, and peri-implantitis is high; premature loss of implants is encountered due to osteointegration process not being completed for some unexplained reasons. However, there is no study in the literature examining the nonfunctional period of implants. Closure screws of different implant companies have different designs like surface properties, and areas, where closure screws sit, are important reservoirs for microorganism colonization. Our study aims to evaluate the inflammatory response, epithelial maturation, and epithelial-connective tissue interaction around closure screws. For this purpose, 52 implants belonging to five different implant companies were included in the study. Tissues removed over the cover screw during fitting of healing caps were used as biopsy material and for epithelial proliferation Ki-67, for epithelium-connective tissue interaction Syndecan-1, and for macrophage activation CD-68 expressions were evaluated by immunohistochemical analysis. Scanning electron microscopy (SEM) analyzes were performed to evaluate the presence of gap between the implant and the cover screw. As a result of our study, intensity of subepithelial inflammation between groups wasn't statistically different. Differences in CD-68 and Syndecan-1 levels were obtained at the lamina propria level. H score of CD-68 was statistically significantly different in epithelium (p = 0.032), and H score of Syndecan-1 was different in lamina propria (p = 0.022). There wasn't a statistically significant difference between the groups for Ki-67 (p = 0.151). Our study results indicate that in addition to the implant surface morphology, the design of the closure screws is important in the inflammatory response and epithelial maturation that develops during wound healing. Although the inflammatory response is required for healing, osteointegration, and implant survival, further investigation is needed to investigate the relationship between initial neck resorption and closure screws with radiographic and microbiological examinations.

Dimension effect on thermal conductivity of hexagonal boron nitride/titanium dioxide reinforced hybrid PEEK composites developed with a scalable compounding approach

AbstractFor the removal of elevated thermal flux in high‐temperature applications, there is an urgent need for robust and lightweight thermally conductive thermoplastic materials with suitable mechanical integrity. In current work, multiscale hexagonal boron nitride (hBN) and titanium dioxide (TiO2) fillers are integrated into polyetheretherketone (PEEK) polymer to create a synergistic effect regarding thermal conductivity. An optimized twin‐screw extrusion is utilized to disperse the fillers uniformly in the host polymer by changing the screw design in terms of kneading, mixing, and reverse elements, feeding zones of the fillers/polymer, and the feeding cycles. Various specimens were developed by systematically varying the relative filler amount of the thermally anisotropic hBN and the thermally isotropic TiO2, while the total filler content was fixed to 60 wt%. As a result, 50B‐10T composite exhibited an ultrahigh thermal conductivity of 8.195 W/(m.K), with a 3139% enhancement compared to unfilled PEEK. Moreover, as the PEEK‐mediated regions are occupied with nano‐sized TiO2, efficient channels for phonon transport are formed between hybrid fillers, and the through‐plane thermal conductivity reached 1.704 W/(m.K) in 50B‐10T sample. The potential application of prepared composites as a heat spreader is demonstrated by monitoring surface temperature distribution and numerical simulation. Meanwhile, we achieved a synchronous improvement in mechanical stiffness within hybrid composites; and failure mechanisms including crack bridging at TiO2‐PEEK interface, and debonding at hBN‐PEEK interface are observed in hybrid composites. Lastly, the high thermal stability makes the PEEK/hBN/TiO2 specimens suitable for heat dissipation in demanding applications in the energy and aerospace sectors.Highlights Bespoke screw design developed for scalable manufacturing of Polyetheretherketone (PEEK) matrix composites reinforced with Hexagonal Boron Nitride (hBN) and Titanium Dioxide (TiO2) via twin‐screw melt compounding. Interconnected 3D filler networks were achieved due to the filler dimension effect, allowing us to reach an ultrahigh in‐plane thermal conductivity value of 8.2 W/(m.K) and through‐plane thermal conductivity value of 1.7 W/(m.K) for 50B‐10T specimen. Manufactured hybrid PEEK/hBN/TiO2 composite specimens possess excellent mechanical stiffness.

Cut-Through versus Cut-Out: No Easy Way to Predict How Single Lag Screw Design Cephalomedullary Nails Used for Intertrochanteric Hip Fractures Will Fail?

This study aims to compare patients in whom fixation failure occurred via cut-out (CO) or cut-through (CT) in order to determine patient factors and radiographic parameters that may be predictive of each mechanism. This retrospective cohort study includes 18 patients with intertrochanteric (IT) hip fractures (AO/OTA classification 31A1.3) who underwent treatment using a single lag screw design intramedullary nail in whom fixation failure occurred within one year. All patients were reviewed for demographics and radiographic parameters including tip-to-apex distance (TAD), posteromedial calcar continuity, neck-shaft angle, lateral wall thickness, and others. Patients were grouped into cohorts based on the mechanism of failure, either lag screw CO or CT, and a comparison was performed. No differences in demographics, injury details, fracture classifications, or radiographic parameters were observed between CO/CT cohorts. Of note, a similar rate of post-reduction TAD>25 mm (P=0.936) was observed between groups. A higher rate of DEXA (dual energy X-ray absorptiometry) confirmed osteoporosis (25.0% vs. 60.0%) was observed in the CT group, but without significance. The mechanism of CT failure during intramedullary nail fixation of an IT fracture did not show an association with clinical data including patient demographics, reduction accuracy, or radiographic parameters. As reported in previous biomechanical studies, the main predictive factor for patients in whom early failure might occur via the CT effect mechanism may be related to bone quality; however, conduct of larger studies will be required in order to determine whether there is a difference in bone quality.

Influence of Simulated State of Disc Degeneration and Axial Stiffness of Coupler in a Hybrid Performance Stabilisation System on the Biomechanics of a Spine Segment Model.

Spinal fusion surgery leads to the restriction of mobility in the vertebral segments postoperatively, thereby causing stress to rise at the adjacent levels, resulting in early degeneration and a high risk of adjacent vertebral fractures. Thus, to address this issue, non-fusion surgery applies some pedicle screw-based dynamic stabilisation systems to provide stability and micromotion, thereby reducing stress in the fusion segments. Among these systems, the hybrid performance stabilisation system (HPSS) combines a rigid rod, transfer screw, and coupler design to offer a semi-rigid fixation method that preserves some mobility near the fusion site and reduces the adjacent segment compensatory effects. However, further research and confirmation are needed regarding the biomechanical effects of the dynamic coupler stiffness of the HPSS on the intrinsic degenerated adjacent segment. Therefore, this study utilised the finite element method to investigate the impact of the coupler stiffness of the HPSS on the mobility of the lumbar vertebral segments and the stress distribution in the intervertebral discs under flexion, extension, and lateral bending, as well as the clinical applicability of the HPSS on the discs with intrinsic moderate and severe degeneration at the adjacent level. The analytical results indicated that, regardless of the degree of disc degeneration, the use of a dynamic coupler stiffness of 57 N/mm in the HPSS may reduce the stress concentrations at the adjacent levels. However, for severely degenerated discs, the postoperative stress on the adjacent segments with the HPSS was still higher compared with that of the discs with moderate degeneration. We conclude that, when the discs had moderate degeneration, increasing the coupler stiffness led to a decrease in disc mobility. In the case of severe disc degeneration, the effect on disc mobility by coupler stiffness was less pronounced. Increasing the coupler stiffness ked to higher stress on intervertebral discs with moderate degeneration, while its effect on stress was less pronounced for discs with severe degeneration. It is recommended that patients with severe degeneration who undergo spinal dynamic stabilisation should remain mindful of the risk of accelerated adjacent segment degeneration.

Stability Analysis of Plate-Screw Fixation for Femoral Midshaft Fractures.

An understanding of the biomechanical characteristics and configuration of flexible and locked plating in order to provide balance stability and flexibility of implant fixation will help to construct and promote fast bone healing. The relationship between applied loading and implantation configuration for best bone healing is still under debate. This study aims to investigate the relationship between implant strength, working length, and interfragmentary strain (εIFM) on implant stability for femoral midshaft transverse fractures. The transverse fracture was fixed with a fragment locking compression plate (LCP) system. Finite element analysis was performed and subsequently characterised based on compression loading (600 N up to 900 N) and screw designs (conventional and locking) with different penetration depths (unicortical and bicortical). Strain theory was used to evaluate the stability of the model. The correlation of screw configuration with screw type shows a unicortical depth for both types (p < 0.01) for 700 N and 800 N loads and (p < 0.05) for configurations 134 and 124. Interfragmentary strain affected only the 600 N load (p < 0.01) for the bicortical conventional type (group BC), and the screw configurations that were influenced were 1234 and 123 (p < 0.05). The low steepness of the slope indicates the least εIFM for the corresponding biomechanical characteristic in good-quality stability. A strain value of ≤2% promotes callus formation and is classified as absolute stability, which is the minimum required value for the induction of callus and the maximum value that allows bony bridging. The outcomes have provided the correlation of screw configuration in femoral midshaft transverse fracture implantation which is important to promote essential primary stability.

An Application of Injection Molding to Semisolid Processing of Metallic Alloys: A Role of SIMA in Feedstock Transformation

Injection molding has proven for over 150 years to be the efficient mass manufacturing technology of net-shape components from plastics, however, its application to metallic alloys, despite four decades of commercialization, still creates challenges. Although early designs assumed a direct replacement of plastic with magnesium, subsequent research revealed essential differences in machinery and processing requirements, imposed by metallic alloys. The key discovery revealed that the dendrite-to-globule transformation during coarse particulate melting is caused by strain induced melt activation (SIMA) due to feedstock deformation imposed at their manufacturing stage, not due to the injection screw shearing during processing. As a result, the process control parameters and the screw and barrel design can be optimized with a focus on other screw functions. That discovery also led to the simplified machinery designs, eliminating the complex injection screw, and replacing it with a simple plunger.

Extended melt‐conveying models for single‐screw extruders: Integrating domain knowledge into symbolic regression

AbstractThe literature provides several analytical approximation methods for predicting the flow of non‐Newtonian fluids in single‐screw extruders. While these are based on various flow conditions, they were developed mostly for extruder screws with standard geometries. We present novel analytical melt‐conveying models for predicting the flow and dissipation rates of fully developed flows of power‐law fluids within three‐dimensional screw channels. To accommodate a broad range of industrial screw designs, including both standard and high‐performance screws, the main intention of this work was to significantly extend the scope of existing theories. The flow equations were first rewritten in a dimensionless form to reduce the mathematical problem to its dimensionless influencing parameters. These were varied within wide ranges to create a set of physically independent modeling setups, the flow and dissipation rates of which were evaluated by means of a finite‐volume solver. The numerical results were then approximated analytically using symbolic regression based on genetic programming. To support the regression analysis in finding accurate solutions, we integrated domain‐specific process knowledge in the preprocessing of the dataset. We obtained three regression models for predicting the flow and dissipation rates in melt‐conveying zones and tested their accuracy successfully against an independent set of numerical solutions.Highlights Flow of power‐law fluids in three‐dimensional screw channels Identification of independent influencing parameters by dimensional analysis Numerical parametric design study for a broad range of industrial applications Integration of domain knowledge in symbolic regression Surrogate models derived from numerical simulation results

P10. Effect of screw design, purchase depth and trajectory on cervical lateral mass fixation strength

P10. Effect of screw design, purchase depth and trajectory on cervical lateral mass fixation strength

Biomechanical evaluation and optimal design of a pedicle screw with double bent rods internal fixation system based on PE-PLIF fusion

Problems, such as broken screws, broken rods, and cage subsidence after clinical spinal fusion surgery affect the success rate of fusion surgery and the fixation effect of fusion segments, and these problems still affect the treatment and postoperative recovery of patients. In this study, we used the biomechanical finite element analysis method to analyze and study the fixation effect of three kinds of spinal internal fixation systems on L4–L5 lumbar spine segments in percutaneous endoscopic posterior lumbar interbody fusion (PE-PLIF). The three different fixation systems compared in this study include bilateral pedicle screw fixation (M1); bilateral pedicle screw with cross-link fixation (M2); bilateral pedicle screws with double bent rods fixation (M3). The internal fixation systems with different structures were analyzed with the help of Hypermesh, and Abaqus. It was found that the internal fixation system with double bent rods reduced screw stresses by 23.8 and 22.2% in right and left axial rotation than the traditional bilateral pedicle screw system, while titanium rod stresses were reduced by 9.6, 3.7, 9.6, and 2.9% in flexion, left and right lateral bending, and right axial rotation, respectively, and L5 upper endplate stresses were reduced by 35.5, 18.9, 38.4, 10.2, and 48.3% in flexion, left and right lateral bending, and left and right axial rotation, respectively. The spinal range of motion (ROM) of the M3 internal fixation system was less than that of the M1 and M2 internal fixation systems in left lateral bending, left lateral rotation, and right axial rotation, and the intact vertebral ROM was reduced by 93.7, 94.9, and 90.9%, respectively. The double bent rod structure of the spinal internal fixation system has better biomechanical properties, which can effectively reduce the risk of screw breakage, loosening, cage subsidence, and endplate collapse after fusion surgery.

Biomechanical Investigation of Bone Screw Head Design for Extracting Stripped Screw Heads: Integration of Mechanical Tests and Finite Element Analyses.

Enhancing the design of bone screw head sockets to prevent stripping and improve the torque required for smooth unscrewing is a significant challenge in orthopedic applications. This research aims to establish a quantitative methodology by integrating mechanical testing with finite element (FE) simulations to determine a safe limitation depth for the screwdriver when engaging with the hexagonal socket, thus avoiding stripped screw heads. A FE model was developed to investigate the biomechanical responses of the screw head design. Five custom-made hexagonal sockets were manufactured, and single load torsional tests were conducted to assess the mechanical performance of the screws and drivers. The results from the mechanical tests were compared with the FE simulations, demonstrating a close agreement and confirming the model's validity. Furthermore, additional FE models were created to study the impact of manufacturing tolerances on the socket width and screwdriver width. The findings revealed that the maximum torque to failure for the four designs was lower than the margins specified in ISO 6475. Additionally, increasing the depth of the screwdriver led to higher maximum torque values. This research suggests that the technique of screw insertion, specifically the depth of the driver tool within the screw socket, holds greater importance in preventing stripped screw heads than the design and manufacturing width of the bone screw's hexagonal socket and screwdriver. This confirms the importance of screwdriver engagement inside the bone screw socket to prevent stripped screw heads and sheds light on the added value of maximum torque prediction for future design modifications.

Is a Washer a Mandatory Component in Young Trauma Patients with S1-S2 Iliosacral Screw Fixation of Posterior Pelvis Ring Injuries? A Biomechanical Study.

Background and purpose: Cannulated screws are standard implants for percutaneous fixa-tion of posterior pelvis ring injuries. The choice of whether to use these screws in combination with a washer is still undecided. The aim of this study was to evaluate the biomechanical competence of S1-S2 sacroiliac (SI) screw fixation with and without using a washer across three different screw designs. Material and Methods: Twenty-four composite pelvises were used and an SI joint injury type APC III according to the Young and Burgess classification was simulated. Fixation of the posterior pelvis ring was performed using either partially threaded short screws, fully threaded short screws, or fully threaded long transsacral screws. Biomechanical testing was performed under progressively increasing cyclic loading until failure, with monitoring of the intersegmental and bone-implant movements via motion tracking. Results: The number of cycles to failure and the corresponding load at failure (N) were significantly higher for the fully threaded short screws with a washer (3972 ± 600/398.6 ± 30.0) versus its counterpart without a washer (2993 ± 527/349.7 ± 26.4), p = 0.026. In contrast, these two parameters did not reveal any significant differences when comparing fixations with and without a washer using either partially threaded short of fully threaded long transsacral screws, p ≥ 0.359. Conclusions: From a biomechanical perspective, a washer could be optional when using partially threaded short or fully threaded long transsacral S1-S2 screws for treatment of posterior pelvis ring injuries in young trauma patients. Yet, the omission of the washer in fully threaded short screws could lead to a significant diminished biomechanical stability.

Effect on osseointegration of dental implants treated with carboxyethylphosphonic acid and functionalized with BMP-2: preliminary study on a minipig model.

Introduction: Rough titanium surfaces biofunctionalised by osteogenic proteins, such as BMP-2, have been shown to accelerate the osseointegration process and reduce waiting times for prosthetic loading. The preclinical study presented here compared the bone in contact with the implant and bone neoformation and density between titanium (Ti) implants with a conventional etched surface (SLA type) and others treated with carboxyethylphosphonic acid (CEPA) and bone morphogenetic protein 2 (BMP-2), after 4weeks of implantation in the tibia of a minipig model. Methods: Sixteen implants (eight experimental and eight control) of Ti-Al16-V4 with a tapered screw design and internal hexagonal connection were randomly inserted into the tibiae of four minipigs, four in each tibia. The experimental implants were treated with CEPA and BMP-2 and sterilised with gamma radiation (25KG). The insertion torque was 40N and primary stability was measured with the Osstell® device (ISQ 64 ± 2.6). Five bone parameters were evaluated: bone in contact with the implant (BIC), bone in contact with the corrected implant (BICc), new bone formation (BV/TV), bone density between threads (BAI/TA) and peri-implant bone density (BAP/TA). A histomorphometric study was performed and the samples were digitised with Adobe Photoshop Cs6. Statistical analysis of the variables was performed using SAS 9.4. Results: After a period of 4weeks, no significant clinical signs were observed and all implants were integrated. Light microscopy of the experimental group revealed an ICB with no signs of fiber tissue, but with areas of ectopic new bone in the medullary space. Statistical analysis showed significant results for BIC and BICc (p = 0.0001 and p = 0.001, respectively). No statistical signification was found for the other parameters evaluated. Conclusion: Despite the limitations of this study, our results demonstrated that dental implant surfaces treated with CEPA and BMP-2 improve their biological response to osseointegration.

A Review and Comparative Study on the Design and Analysis of Magnetic Lead Screws

A Review and Comparative Study on the Design and Analysis of Magnetic Lead Screws

Biomechanical comparison of compact versus standard flute drill bits, and interlocking versus buttress thread self-tapping cortical bone screws in cadaveric equine third metacarpal condyle.

To compare (1) performance of compact versus standard flute drill bits, (2) screw insertion properties and (3) pullout variables between interlocking thread (ITS) and buttress thread (BTS) self-tapping screws in third metacarpi. In vitro experimental study. Paired third metacarpi from 11 Thoroughbreds aged 2-4 years. Screws were inserted into the lateral condylar fossae following bone preparation using the respective drill bit for each screw type. Screw pullout was achieved using a mechanical testing system. Density and porosity of bone surrounding screw holes was measured with microcomputed tomography following each pullout test. Drilling, screw insertion and pullout variables were compared between drill bit and screw types using repeated measures ANOVA. Linear regression analyses were used to characterize relationships between bone tissue properties and drill bit and screw outcomes. Maximum torque power spectral density (PSD) was lower for compact flute drill bits. Insertion torque was 50% higher for ITS. BTS had 33% greater preyield stiffness and 7% greater mean yield force. Bone tissue properties affected measured variables similarly for both screw and drill bit types. Lower torque PSD may increase durability of the compact flute drill bit. ITS had greater insertional torque, which may reflect greater bone engagement. BTS had greater resistance to axial pullout forces. Metacarpal bone provides a simple model for comparison of drill bit and screw designs. Use of ITS to repair equine fractures subject to predominantly tensile forces is not justified based on the results of this study.

Pullout Strength of Pedicle Screws Inserted Using Three Different Techniques: A Biomechanical Study on Polyurethane Foam Block

Pullout strength is an important indicator of the performance and longevity of pedicle screws and can be heavily influenced by the screw design, the insertion technique and the quality of surrounding bone. The purpose of this study was to investigate the pullout strength of three different pedicle screws inserted using three different strategies and with two different loading conditions. Three pedicle screws with different thread designs (single-lead-thread (SLT) screw, dual-lead-thread (DLT) screw and mixed-single-lead-thread (MSLT) screw) were inserted into a pre-drilled rigid polyurethane foam block using three strategies: (A) screw inserted to a depth of 33.5 mm; (B) screw inserted to a depth of 33.5 mm and then reversed by 3.5 mm to simulate an adjustment of the tulip height of the pedicle screw and (C) screw inserted to a depth of 30 mm. After insertion, each screw type was set up with and without a cyclic load being applied to the screw head prior to the pullout test. To ensure that the normality assumption is met, we applied the Shapiro–Wilk test to all datasets before conducting the non-parametric statistical test (Kruskal–Wallis test combined with pairwise Mann–Whitney-U tests). All screw types inserted using strategy A had a significantly greater pullout strength than those inserted using strategies B and C, regardless of if the screw was pre-loaded with a cyclic load prior to testing. Without the use of the cyclic pre-load, the MSLT screw had a greater pullout strength than the SLT and DLT screws for all three insertion strategies. However, the fixation strength of all screws was reduced when pre-loaded before testing, with the MSLT screw inserted using strategy B producing a significantly lower pullout strength than all other groups (p &lt; 0.05). In contrast, the MSLT screw using insertion strategies A and C had a greater pullout strength than the SLT and DLT screws both with and without pre-loading. In conclusion, the MSLT pedicle screw exhibited the greatest pullout strength of the screws tested under all insertion strategies and loading conditions, except for insertion strategy B with a cyclic pre-load. While all screw types showed a reduced pullout strength when using insertion strategy B (screw-out depth adjustment), the MSLT screw had the largest reduction in pullout strength when using a pre-load before testing. Based on these findings, during the initial screw insertion, it is recommended to not fully insert the screw thread into the bone and to leave a retention length for depth adjustment to avoid the need for screw-out adjustment, as with insertion strategy B.

Study on the Selection of Single-Screw Steam Compressors in Industrial Steam Supply

Both direct and indirect heating compression methods were proposed to satisfy the requirement of industrial steam compression and supply. The compression process in a single-screw compressor was analyzed with the determination of different inlet and outlet boundary conditions. Considering the misalignment of meshing pairs caused by the offset of the star wheel axis and screw origin, the differential expansion of the vertical meshing pair was further analyzed. The inner ring of the sealing end face, the wall of the inner ring of the bearing at the inlet and outlet ends, and the bottom surface of the bracket were analyzed by different coordinate systems and different constraints, thus facilitating the design and selection of the single screw. The critical point for the design of a steam-type single-screw compressor is an outlet temperature of 350 °C and an outlet volume flow rate of 130 m3/min. At a flow rate of 130 m3/min, when the temperature exceeds 350 °C, the reliability of the compressor is still limited, and the differential expansion of the meshing pair exceeds 0.3 mm. In addition, superheating of steam can be improved by applying a centrifugal compressor with cascade compression and centrifugal compression in conjunction with reflux adjustment at the compression outlet.

Fixation-induced surgical segment’s high stiffness and the damage of posterior structures together trigger a higher risk of adjacent segment disease in patients with lumbar interbody fusion operations

BackgroundAdjacent segment disease (ASD) is a commonly reported complication after lumbar interbody fusion (LIF); changes in the mechanical environment play an essential role in the generation of ASD. Traditionally, fixation-induced high stiffness in the surgical segment was the main reason for ASD. However, with more attention paid to the biomechanical significance of posterior bony and soft structures, surgeons hypothesize that this factor may also play an important role in ASD.MethodsOblique and posterior LIF operations have been simulated in this study. The stand-alone OLIF and OLIF fixed by bilateral pedicle screw (BPS) system have been simulated. The spinal process (the attachment point of cranial ligamentum complex) was excised in the PLIF model; the BPS system has also been used in the PLIF model. Stress values related to ASD have been computed under physiological body positions, including flexion, extension, bending, and axial rotations.ResultsCompared to the stand-alone OLIF model, the OLIF model with BPS fixation suffers higher stress values under extension body position. However, there are no apparent differences under other loading conditions. Moreover, significant increases in stress values can be recorded in flexion and extension loading conditions in the PLIF model with posterior structures damage.ConclusionsFixation-induced surgical segment’s high stiffness and the damage of posterior soft tissues together trigger a higher risk of ASD in patients with LIF operations. Optimizing BPS fixation methods and pedicle screw designs and reducing the range of posterior structures excision may be an effective method to reduce the risk of ASD.