Screw Type Research Articles

Incidence of and Risk Factors for Screw Loosening after Iliosacral Screw Fixation for Posterior Pelvic Ring Injury.

Screw loosening is a common complication of iliosacral screw fixation, with subsequent loss of stability and fracture re-displacement. This study aimed to investigate the incidence of and risk factors for screw loosening after iliosacral screw fixation for posterior pelvic ring injury. A total of 135 patients with posterior pelvic ring injuries who were treated with iliosacral screw fixation in our department between July 2015 and April 2021 were selected for this retrospective analysis. The possible risk factors for screw loosening were investigated using univariate and multivariate logistic regression analyses of patient demographics and trauma-related and iatrogenic variables, including age, sex, body mass index, Osteoporosis Self-Assessment Tool for Asians (OSTA) index, mechanism of injury, Young-Burgess classification, site of injury, type of injury, type of screw, mode of fixation, numbers of guidewire adjustments, accuracy of screw position, and quality of fracture reduction. The incidence of screw loosening was 15.6% (n = 21). The mean duration for screw loosening was 3.2 ± 1.5 months after operation. Univariate analysis results showed that the Young-Burgess classification, type of injury, site of injury, type of screw, mode of fixation, and OSTA index might be related to screw loosening (p < 0.05). According to the multivariate logistic regression, vertical shear injuries (Odds ratios [OR] 9.80, 95% Confidence intervals [CI] [1.96-73.28], p = 0.008), type of injury (OR 0.25, 95% CI [0.13-0.79], p = 0.027), common screws (OR 6.94, 95% CI [1.53-31.40], p = 0.012), screws insertion only at the level of the first sacral segment (S1) (OR 8.79, 95% CI [1.18-65.46], p = 0.034), injury site located in the medial sacral foramina (OR 6.28, 95% CI [1.16-34.06], p = 0.033), and lower OSTA index [OR 0.41, 95% CI [0.24-0.71], p = 0.001] were significantly related to screw loosening. Vertical shear injuries, sacral fractures, injury site located in the medial sacral foramina, and lower OSTA index are significantly associated with the postoperative occurrence of screw loosening. Transiliac-transsacral screw fixation and screws insertion both at the level of the S1 and second sacral segment can prevent screw loosening.

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.

Metal artifact reduction and clinical verification in oral and maxillofacial region based on deep learning

Objective: To construct a kind of neural network for eliminating the metal artifacts in CT images by training the generative adversarial networks (GAN) model, so as to provide reference for clinical practice. Methods: The CT data of patients treated in the Department of Radiology, West China Hospital of Stomatology, Sichuan University from January 2017 to June 2022 were collected. A total of 1 000 cases of artifact-free CT data and 620 cases of metal artifact CT data were obtained, including 5 types of metal restorative materials, namely, fillings, crowns, titanium plates and screws, orthodontic brackets and metal foreign bodies. Four hundred metal artifact CT data and 1 000 artifact-free CT data were utilized for simulation synthesis, and 1 000 pairs of simulated artifacts and metal images and simulated metal images (200 pairs of each type) were constructed. Under the condition that the data of the five metal artifacts were equal, the entire data set was randomly (computer random) divided into a training set (800 pairs) and a test set (200 pairs). The former was used to train the GAN model, and the latter was used to evaluate the performance of the GAN model. The test set was evaluated quantitatively and the quantitative indexes were root-mean-square error (RMSE) and structural similarity index measure (SSIM). The trained GAN model was employed to eliminate the metal artifacts from the CT data of the remaining 220 clinical cases of metal artifact CT data, and the elimination results were evaluated by two senior attending doctors using the modified LiKert scale. Results: The RMSE values for artifact elimination of fillings, crowns, titanium plates and screws, orthodontic brackets and metal foreign bodies in test set were 0.018±0.004, 0.023±0.007, 0.015±0.003, 0.019±0.004, 0.024±0.008, respectively (F=1.29, P=0.274). The SSIM values were 0.963±0.023, 0.961±0.023, 0.965±0.013, 0.958±0.022, 0.957±0.026, respectively (F=2.22, P=0.069). The intra-group correlation coefficient of 2 evaluators was 0.972. For 220 clinical cases, the overall score of the modified LiKert scale was (3.73±1.13), indicating a satisfactory performance. The scores of modified LiKert scale for fillings, crowns, titanium plates and screws, orthodontic brackets and metal foreign bodies were (3.68±1.13), (3.67±1.16), (3.97±1.03), (3.83±1.14), (3.33±1.12), respectively (F=1.44, P=0.145). Conclusions: The metal artifact reduction GAN model constructed in this study can effectively remove the interference of metal artifacts and improve the image quality.

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.

Adverse events associated with AveirTM VR leadless pacemaker: A Food and Drug Administration MAUDE database study.

Leadless pacemaker (LP) offers an innovative approach for treating bradyarrhythmia, thus avoiding pacemaker pocket and lead-related complications. The Food and Drug Administration (FDA) has recently approved the Aveir™ leadless pacing system (screw-in type LP). We queried the FDA MAUDE database to study the safety profile and assess the types of complications with this relatively novel device technology. A MAUDE database search was conducted on January 20, 2023, for reports received post-FDA approval to capture all adverse events. A total of 98 medical device report were reported for Aveir™ LP. After excluding duplicate, programmer-related, or introducer-sheath-related entries (n = 34), 64 entries were included. The most commonly encountered problem was high threshold/noncapture (28.1%, 18 events), followed by stretched helix (17.2%, 11 events) and device dislodgement (15.6%, ten events-5 intraprocedural, while 5 in the postoperative Day 1). Other reported events included high impedance (14.1%, nine events), sensing issues (12.5%, eight events), bent/broken helix (7.8%, five events), premature separation (4.7%, three events), interrogation problem (3.1%, two events), low impedance (3.1%, two events), premature battery depletion (1.6%, one event) and inadvertent MRI mode switch (1.6%, one event) and miscellaneous (15.6%, n = 10). There were eight serious patient injury events-pericardial effusion requiring pericardiocentesis (7.8%, five events) due to cardiac perforation that resulted in two deaths (3.1%) followed by sustained ventricular arrhythmias (4.6%, n = 3). In our study assessing the real-world safety profile of the Aveir™ LP, serious adverse events have been reported-life-threatening ventricular arrhythmias, pericardial effusion, device explantation/reimplantation, and death.

Evolutionary Multi-Objective Optimization of Extrusion Barrier Screws: Data Mining and Decision Making.

Polymer single-screw extrusion is a major industrial processing technique used to obtain plastic products. To assure high outputs, tight dimensional tolerances, and excellent product performance, extruder screws may show different design characteristics. Barrier screws, which contain a second flight in the compression zone, have become quite popular as they promote and stabilize polymer melting. Therefore, it is important to design efficient extruder screws and decide whether a conventional screw will perform the job efficiently, or a barrier screw should be considered instead. This work uses multi-objective evolutionary algorithms to design conventional and barrier screws (Maillefer screws will be studied) with optimized geometry. The processing of two polymers, low-density polyethylene and polypropylene, is analyzed. A methodology based on the use of artificial intelligence (AI) techniques, namely, data mining, decision making, and evolutionary algorithms, is presented and utilized to obtain results with practical significance, based on relevant performance measures (objectives) used in the optimization. For the various case studies selected, Maillefer screws were generally advantageous for processing LDPE, while for PP, the use of both types of screws would be feasible.

MP-453087-5 ADVERSE EVENTS ASSOCIATED WITH AVEIRTMVR LEADLESS PACEMAKER: A FOOD AND DRUG ADMINISTRATION MAUDE DATABASE STUDY

Since the first pacemaker implantation, much of the effort has been focused on battery longevity and device miniaturization. Leadless pacemaker offers an innovative approach to the treatment of bradyarrhythmias, thus avoiding long-term lead-related complications. Recently, the Aveir (screw-in type leadless pacemaker) (Abbott) has been approved by the Food and Drug Administration (FDA). We queried the FDA Manufacturer And User Facility Device Experience (MAUDE) database to study the safety profile and assess the types of complications with this relatively novel device technology. The MAUDE database is a repository of industry and patient/physician-reported medical device adverse events. A MAUDE database search was conducted on November 10, 2022, for reports received post-FDA approval to capture all adverse events. A total of 42 events (after removing duplicate entries or programmer or introducer sheath-related issues n=13) were reported for Aveir leadless pacemaker post-FDA approval. The most frequently reported issue was a device malfunction-related event (n=36, 85.7%). The most commonly encountered problem was the capture issue (28.6%, 12 events), followed by the sensing issue (19%, 8 events), high impedance (19%, 8 events), stretched helix (19%, 8 events), device dislodgement (14.3%, 6 events), device separation failure (14.3%, 6 events), premature separation (4.8%, 2 events), material twist (4.8%, 2 events), and broken helix (2.4%, 1 event). As such, this resulted in pericardial effusion requiring pericardiocentesis (9.5%, 4 events), cardiac perforation (9.5%, 4 events), and arrhythmia (2.4%, 1 event). This resulted in one death. Aveir leadless pacemaker implantation may be complicated by myocardial perforations and tears that result in cardiac tamponade and death. Our study is limited by heterogeneity in reporting, and lack of assessment of the total number of cases performed per year; thus, warranting better transparency and monitoring mechanisms.

Design Features of the Screw Unit for Processing Bulk Substances

This article is devoted to the description of the multifunctional energy converter (MFEC) design of the screw type. MFEC is an induction motor with an external hollow solid rotor. On the surface of the rotor, which is a steel pipe, the turns of the screw conveyer are welded. When supplying power to the stator winding (which visually resembles the wound rotor of an induction motor), the magnetic field not only causes the rotor to rotate, but also, due to the formation of eddy currents, heats the latter. Thus, the idea of combining several functional components is realized in one device: mixing, heating and transportation along the turns of the screw of bulk material. The specified operations are implemented without the use of an external electric drive, heaters, but only due to the principle of operation of the MFEC. Previously, the two-module design of the MFEC was investigated, but experimental studies indicated certain shortcomings of the chosen approach. In this work, an attempt is made to show an alternative configuration of the MFEC, based on the execution of independent single modules that can be combined into a continuous screw thanks to transitional fasteners. In addition, the approach to the power supply and module management system has been revised. This article is one of a series of works devoted to a detailed description of the design of the MFEC.

Immediate and late inflammatory and bone healing response post implantation of self-tapping and self-drilling osteosynthesis screws

The aim of this study was to comparatively analyse osseointegration after the implantation of self-tapping screws (STS) and self-drilling screws (SDS). Thus, 24 four-month-old male Wistar rats, received SDS and STS screws in their left and right tibias, respectively. Sample collection was performed immediately at 0 hours (0h), two, seven, and 21 days after implantation (2d, 7d, 21d). Samples from immediately and 21 days after were analysed by micro computed tomography (MicroCT). All time points were evaluated by histology (Haematoxylin and Eoisin and Goldner's Trichrome) and immunohistochemistry for tartrate-acid resistant phosphatase positive (TRAP+) osteoclasts. MicroCT images revealed an intimate contact between bone and each type of screw at 0h. However, SDS group presented decreased bone volume (BV, mm3) at 21 days in comparison with STS. Both SDS and STS post implantation presented areas of suitable new bone formation surrounding screw threads from seven days, and inflammation decreased from two to 21 days. Also, TRAP+ osteoclasts were mainly identified at seven days in both STS and SDS groups, particularly surrounding areas of pressure, with significant differences between groups. In conclusion, differences in shape and insertion technique for SDS and STS screws did not affect immediate and late inflammatory and bone healing response post implantation in this animal model. Both osteosynthesis screws allowed satisfactory post-surgical outcomes.

Stress Shielding Prediction of Unicortical and Bicortical Screws: A Finite Element Analysis

The stability in an implant fixation plays a vital role in ensuring proper formation and remodelling process of the fractured bone. Failure in implant fixation is commonly associated with short- and long-term instability of the bone-implant interface. The bone-implant interaction creates a complicated mechanical interplay that might influence the stress distribution and hence the biomechanical performance stability of the implant fixation. Furthermore, implant screw parameters namely thread size, geometrical design and material properties become additional factors that affect the bone-implant interaction. The purpose of this study was to investigate the effect of unicortical and bicortical screws’ parameters on the screw-bone interaction mechanism. To evaluate the stress transfers between screw and bone, the stress parameters namely stress transfer parameters (STP) was employed. A two-dimensional (2D) finite element model of full treaded screw was simulated while varying the parameters of the screw: two types of material (stainless steel A316 and titanium alloy Ti-6Al-4V), screw length and screw pitch. It was found that the lower in elastic modulus results to the higher stress transfer between implant- bone interface. As the titanium have lower elastic modulus, it gave higher values of STP which help to transmit and distribute stress better compared to the stainless steel. While the effect of varying screw pitch between two types of screws shows that STPs values of fully threaded bicortical screws shows significant result for finer pitch size that may advancing bone remodelling process at the early stage.

A Novel Pedicle Screw Design with Variable Thread Geometry: Biomechanical Cadaveric Study with Finite Element Analysis.

Pedicle screw fixation provides one of the most stable spinal constructs. Their designs together with osseous characteristics have been known to influence the screw-bone interplay during surgical maneuvers and thereafter the fusion process. Various technical modifications to enhance screw performance have been suggested. This study evaluated the pull-out strength and axial stiffness of a novel pedicle screw design with variable thread geometry and pitch. The newly designed triple threaded pedicle screw is tapered, and has unique out-turned flanges to hold the cancellous bone and a finer pitch at its distal and proximal end to engage the cortical bone. Five lumbar and 4 lower thoracic cadaveric vertebrae were divided into hemivertebrae. A standard cancellous pedicle screw and the newly designed pedicle screw were inserted into each hemivertebra. Axial stiffness and peak pull-out force between the screw types were compared; a finite element analysis was also performed to additionally compare the pull out under toggle forces. In cadaveric study, the axial stiffness of the new screw was significantly better than that of the standard screw. However, the peak load between the screws was not statistically different. Finite element analyses suggested lesser stress at bone-implant interface for the new screw along with better axial stiffness under both co-axial and toggle forces. Our novel pedicle screw design with variable thread geometry demonstrates greater axial stiffness compared with the standard screws, and therefore is likely to withstand a greater surgical manipulation.

Robotics in Cervical Spine Surgery: Feasibility and Safety of Posterior Screw Placement.

Robot-assisted (RA) techniques have been widely investigated in thoracolumbar spine surgery. However, the application of RA methods on cervical spine surgery is rare due to the complex morphology of cervical vertebrae and catastrophic complications. Thus, the feasibility and safety of RA cervical screw placement remain controversial. This study aims to evaluate the feasibility and safety of RA screw placement on cervical spine surgery. A comprehensive search on PubMed, Cochrane Library, Embase Database, Web of Science, Chinese National Knowledge Databases, and Wanfang Database was performed to select potential eligible studies. Randomized controlled trials (RCTs), comparative cohort studies, and case series reporting the accuracy of cervical screw placement were included. The Cochrane risk of bias criteria and Newcastle-Ottawa Scale criteria were utilized to rate the risk of bias of the included literatures. The primary outcome was the rate of cervical screw placement accuracy with robotic guidance; subgroup analyses based on the screw type and insertion segments were also performed. One RCT, 3 comparative cohort studies, and 3 case series consisting of 160 patients and 719 cervical screws were included in this meta-analysis. The combined outcomes indicated that the rates of optimal and clinically acceptable cervical screw placement accuracy under robotic guidance were 88.0% (95% confidence interval [CI], 84.1%-91.4%; p = 0.073; I2 = 47.941%) and 98.4% (95% CI, 96.8%-99.5%; p = 0.167; I2 = 35.954%). The subgroup analyses showed that the rate of optimal pedicle screw placement accuracy was 88.2% (95% CI, 83.1%-92.6%; p = 0.057; I2 = 53.305%); the rates of optimal screw placement accuracy on C1, C2, and subaxial segments were 96.2% (95% CI, 80.5%-100.0%; p = 0.167; I2 = 44.134X%), 89.7% (95% CI, 80.6%-96.6%; p = 0.370; I2 = 0.000X%), and 82.6% (95% CI, 70.9%-91.9%; p = 0.057; I2 = 65.127X%;), respectively. RA techniques were associated with high rates of optimal and clinically acceptable screw positions. RA cervical screw placement is accurate, safe, and feasible in cervical spine surgery with promising clinical potential.

Effects of viscosity modifying admixture and nanoclay on fresh and rheo-viscoelastic properties and printability characteristics of cementitious composites

This study explores the effects of a viscosity modifying admixture (VMA) and attapulgite nanoclay (ANC) on rheological and viscoelastic properties as well as printability characteristics of mortar mixtures used for 3D printing. A total of sixteen mortar mixtures with varying dosages of VMA and ANC are prepared using a factorial design of experiments. Rheological properties of each mixture including static yield stress, plastic viscosity, and dynamic yield stress are evaluated through rotational rheometry tests such as ramp test and stress growth test. Then, the viscoelastic properties such as storage modulus, loss modulus and linear viscoelastic range are determined using oscillatory rheology tests. A thermogravimetric analysis (TGA) is conducted to assess the effects of VMA and ANC on hydration characteristics of mortar mixtures. A statistical analysis is performed to further evaluate the individual and joint effects of VMA and ANC on key performance parameters. An unsupervised clustering algorithm is used to group the mixtures into three clusters based on the obtained rheological and viscoelastic properties. A direct printing test using a screw type 3D concrete printing is conducted to assess the printability and buildability of the mortar mixtures selected from each cluster. Results indicate that the ANC can more effectively alter both rheological and viscoelastic properties of mortar composites for 3D printing compared with VMA. However, the combined use of VMA and ANC in printable mortar mixtures leads to a high static yield stress and storage modulus and the resulted mixture exhibits good buildability without any plastic collapse.

A study into the effect of material deposition methods on hardened properties of 3D printed concrete

Concrete 3D printing (3DCP) is a novel construction method that uses the principle of additive manufacturing (AM) to build the concrete structure in a layered fashion directly from 3D computer aided digital model. Out of several AM techniques, extrusion-based 3D printing was widely used for AM of concrete structures. However, unlike the metal and polymer, concrete structures are expected to be high rise, hence the use of pumping of concrete is needed to avoid manual material loading in a typical screw driven extruder. This paper investigates the effects of these two material deposition methods such as direct pumping and screw based extrusion on hardened properties of the printed structures. From the experimental results, it was found that the maximum strength of the pumped specimens was around 68 MPa in 28 days which is close to casted strength (72 MPa). Even the pumped specimens gave higher mechanical strength with lesser anisotropic variation compared to the extruded specimens, irrespective of the change in layer height. The maximum compressive strength of the printed specimens decreased from 30% to 10% as layer height increased (from 10 mm to 15 mm) for extruded and pumped specimens, respectively. The cross sectional view of the printed specimens was used to compute the percentage of porosity, which was then connected with the percentage of layer overlap of the ideal mathematical sketches. These results are further backed with bond strength data which indicates 22 % higher inter layer and 33 % higher intra layer bond strength of the pumped specimens when compared to the extruded specimens of 10 mm layer height print.

Design, fabrication and evaluation of a screw type pelletizer with an interchangeable auger

Design, fabrication and evaluation of a screw type pelletizer with an interchangeable auger

Effect of Si on the dislocation state within martensite of ultra-high strength hot-rolled medium Mn steel with good ductility

Medium Mn steels are promising candidates for the third-generation advanced high-strength steels due to their good combination of ultimate tensile strength (UTS) and total elongation after fracture (TEL). Most investigations of medium Mn steels focused on the volume fraction of retained austenite (RA) and stability of RA; however, the strengthening phase martensite was paid little attention to. The present study systematically investigated the effect of Si on the deformation behavior of martensite in 0.2C–6.8Mn-(0, 2, 4)Si (wt. %) hot-rolled medium Mn steels without any heat treatment. The UTS and TEL of the 4Si hot-rolled medium Mn steel are 2163 MPa and 11.7%, respectively, which is rare in the existing hot-rolled medium Mn steels. All three hot-rolled steels had practically equal fraction and mechanical stability of RA, so that the influence of Si on the evolution of martensite fine structure and the nature of the ultra-high UTS and good ductility during deformation could be revealed. By combining the X-ray and neutron diffraction techniques, it was found that the addition of Si increased the dislocation density, especially screw dislocations, and decreased the crystallite size within martensite. The ultra-high UTS originates from the enhanced strain hardening rate caused by the Si alloying, high dislocation density and possibly increased number of martensite lath boundaries and dislocation cell formation. The good ductility mainly stems from the formation of dislocation cell structure due to the addition of Si causing dislocations to be mostly of screw type. The dislocation cells can also improve the strain hardening rate. This work opens a new pathway towards tailoring the dislocation state within martensite for substantially enhanced the mechanical properties of hot-rolled medium Mn steels.

Photoluminescence Properties of InGaN/InGaN MQWs with Different Electron Injection Layers

The structural and optical properties of InxGa1-xN/InyGa1-yN multi quantum well (MQW) light emitting devices with/without electron injection layers were studied. The samples with electron injection layer consist of step-graded (GIE) and two step staircase (SEI) electron injection layer between n-type GaN and MQWs active region. Edge and screw type of dislocation densities were deduced from High Resolution X-Ray Diffraction (HR-XRD) curves and no significant difference were realized. The zeroth and higher order satellite peaks were more clearly observed in the sample without electron injection layer. Optical characterization was carried out by temperature dependent photoluminescence (PL) technique. It was found that the PL densities of samples with step-graded and two step-staircase electron injection layers had almost two times lower temperature dependence compared to the reference sample without electron injection layer. On the other hand, the line width of the photoluminescence peak associated with MQWs is much narrower at low temperature for sample without electron injection layer than the other two samples.

Type synthesis of serial kinematic chains with screw type terminal constraints based on an adding joint method

Serial kinematic chains(SKCs) with screw type terminal constraints are ubiquitous. However, the type synthesis of such mechanisms has not been systematically studied. Unlike the SKCs which only have pure constraint forces and torques, these kinds of SKCs contain independent screw type terminal constraints with non-zero pitch. This paper develops a systematic work for the type synthesis of general SKCs with terminal screw type constraints. In this paper, combined with the screw theory and the atlas method, the principle and steps for synthesizing SKCs based on an adding joint method are proposed. To derive feasible SKCs with terminal screw type constraints, the concept of constraint-kinematic identification graph(CKIG) is proposed and used to identify the screw type constraints in SKCs. Based on the proposed approach, varied 4R, 3R1P and 2R2P SKCs with 1F1H and 1C1H type terminal constraints and numerous 5R, 4R1P and 3R2P SKCs with 1H type terminal constraint are obtained. In addition, some examples for constructing novel parallel mechanisms(PMs) using the derived SKC with screw type terminal constraints are given. This paper provides an effective method for the type synthesis of SKCs with screw type terminal constraints.

Design and Characterization of Mg Alloy Pedicle Screws for Atlantoaxial Fixation

To investigate the feasibility of using absorbable Mg alloy pedicle screws for atlantoaxial dislocation fixation, four types of Mg alloy pedicle screws of different thread forms were designed, and simulation analysis of the pull-out force was performed using the finite element method. Stress and displacement distributions of the atlantoaxial fixation model were obtained. Subsequently, screw samples were prepared using the WE43 Mg alloy for extraction, torsion, and immersion corrosion tests. Finite element analysis results showed that the pull-out forces of triangular, rectangular, trapezoidal, and zigzag thread screws were 552.61, 540.91, 546.4, and 542.74 N, respectively, and the stresses on the screws were 146, 185, 195, and 265 MPa, respectively, when they were pulled out. In other words, the triangular thread screw had the largest pull-out resistance and smallest stress peak. The average corrosion rate of Mg alloy screws in vitro was 0.46 mg·cm−2·day−1. Compared with that before corrosion, the extraction resistance of the corroded screws did not change significantly; however, the torsional strength decreased, but it was still greater than the torque required for screw implantation. It can be concluded that triangular thread Mg alloy pedicle screws have good extraction resistance and mechanical stability and can meet the load-bearing requirements for atlantoaxial dislocation fixation. The degradation of the Mg alloy reduced the mechanical strength of the screws, but the triangularly threaded screws can still maintain their effectiveness.

Blood Loss Following Open Posterior Spinal Fusion in Fractures: Cannulated vs. Solid Pedicle Screws.

We aim to delineate whether there is increased blood loss with the use of cannulated pedicle screws compared to solid pedicle screws in patients undergoing posterior spinal fusion. A single-centre retrospective case-control study was undertaken on patients undergoing PSF for spinal fractures. Cannulated screw fixation was compared with solid screw fixation. Intraoperative blood loss was estimated using pre and postoperative haemoglobin levels, recorded estimated blood loss and cell saver reports. Anticoagulation, blood product administration, operative time and number of levels fused were assessed. A total of 64 cases, 32 in each cohort, were included in the analysis. Overall mean haemoglobin reduction from pre- to post-operative was 2.82 ± 1.85 g/L per screw inserted in the cannulated group, compared to a haemoglobin decrease of 2.81 ± 1.521 g/L per screw inserted in the solid screw group (p = 0.971). Total estimated intraoperative blood loss was 616.3 + 355.4 mL in the cannulated group, compared to 713.6 + 473.5 mL in the solid screw group (p = 0.456). Patients with preoperative thrombocytopenia had a transfusion rate of 0.5 ± 0.71 units/patient compared to 0.04 ± 0.19 units/patient in patients with normal platelet levels (p < 0.005). The differences in blood loss observed between cannulated and solid pedicle screws are non-significant overall. The largest predictor for need of transfusion was pre-operative thrombocytopenia, regardless of the type of screw used.