Screw Configuration Research Articles

Initial stability and stress distribution of ankle arthroscopic arthrodesis with three kinds of 2-screw configuration fixation: a finite element analysis

BackgroundArthroscopic ankle arthrodesis (AAA) is recognized as the standard treatment for the end-stage ankle arthritis. Two-screw configuration fixation is a typical technique for AAA; however, no consensus has been reached on how to select most suitable inserted position and direction. For better joint reduction, we developed a new configuration (2 home run-screw configuration: 2 screws are inserted from the lateral-posterior and medial-posterior malleolus into the talar neck) and investigated whether it turned out to be better than the other commonly used 2-screw configurations.MethodsIn this study, we investigated three kinds of 2-screw configurations: 2 “home run”-screw configuration (group A), crossed transverse configuration (the screw is inserted from the medial malleolus into the anterior talus and the other from the lateral tibia maintains posterior talus, group B), and 2 parallel screw configuration (2 parallel screws are inserted from the posteromedial side of the tibia into talus, group C). The effects of the above three insertions on the loading stress of the tibio-talar joint were comparatively analyzed with a three-dimensional finite element model.ResultsGroup A was better than groups B and C in respect of stress distribution uniformity and superior to both groups B and C in anti-flexion strength and anti-internal rotation strength. Group A was slightly worse than group C but better than group B in anti-dorsiflexion and anti-valgus and varus strength.ConclusionsTwo “home run”-screw configuration facilitates the reduction of anterior talus dislocation of end-stage ankle arthritis. Our finite element analysis demonstrates the configuration is superior to crossed transverse and parallel configuration for arthroscopic ankle arthrodesis in terms of stress distribution and initial stability.

Dissolution improvement of an active pharmaceutical ingredient in a polymer melt by hot melt extrusion

Abstract Dissolution of poorly water-soluble active pharmaceutical ingredients (APIs) in polymeric melts plays an important role in the manufacturing of solid dispersions and solid solutions. The understanding of the dissolution is essential for selecting the processing equipment, the operating conditions, and the polymer excipients. The methodology presented in this work for ketoprofen (KTO) and polymer excipients serves as a screening process to select the best API-polymer formulation for hot melt extrusion (HME) to target a specific release profile. KTO dispersion within the polymer was characterized by differential scanning calorimetry (DSC), X-ray diffraction (XRD), and dissolution tests. Thermal characterization shows that a single phase amorphous solid solution (one glass transition temperature [Tg]) was achieved under the HME processing conditions and screw configuration; and with the combination of polymer excipients, an extended release profile of KTO was accomplished, releasing 100% of KTO in 24 h.

Continuous twin screw wet granulation: The combined effect of process parameters on residence time, particle size, and granule morphology

In this study, a set of 24 experiments was designed to understand the combined effect of different process parameters, i.e. material feed rate, liquid-to-solid (L/S) ratio, screw speed, and screw configuration on the residence time distribution, granule morphology, and particle size distribution in twin screw wet granulation of microcrystalline cellulose. It was shown that residence times were longer at higher L/S and lower screw speeds. However, the most dominant effect on mean residence time had screw configuration, with longer residence times observed with increasing complexity of the screws employed. Scanning electron microscopy and laser diffraction measurements showed accordingly that the most important quality attribute affecting size of granules is L/S ratio. The relationships between input and output parameters observed for our low throughput setup generally match those concerning higher throughput granulators described in literature.

Implant Removal Matrix for the Foot and Ankle Orthopaedic Surgeon.

Orthopaedic surgery frequently requires the use of metal plate and screw constructs for osteosynthesis. These constructs may be subsequently removed for a variety of indications. In the lower extremity in particular, implants (ie, hardware) can lead to prominence and pain secondary to a thin soft-tissue envelope with little subcutaneous tissue. Often, removal is performed without knowledge of the exact type of screw head configuration and/or size, which can make removal technically challenging. The purpose of this study is to consolidate screw head sizes and configurations from commonly utilized orthopaedic foot and ankle implant manufacturers matched against 2 commonly used universal implant removal sets to aid in the expeditious removal of hardware. Orthopaedic manufacturers of foot and ankle-specific implants were included based on market share. Publicly available information on screw size, head configuration, and driver size was collected and recorded. This information was cross-referenced against the drivers available in 2 commonly utilized universal implant removal sets. Seven foot and ankle implant manufacturers were included. The data were compiled in table format according to manufacturer and subcategorized by noncannulated screws, cannulated screws, and locking screws. Many factors affect the success of hardware removal, and it is imperative that the surgeon knows which drivers are compatible with the implanted hardware. The expanding magnitude and diversity of orthopaedic implants makes removal of hardware more challenging. A guide of compatible drivers for various screw types helps expedite this procedure. Level V.

Effect of composite bone plates on callus generation and healing of fractured tibia with different screw configurations

In this paper, finite element analysis of a fractured tibia with a glass/polypropylene composite implant is introduced. A rejection coefficient algorithm (for callus development) that is sensitive to interfragmentary movement is programmed, calibrated (using experimental in vivo statistics), and successfully implemented on a 3D fractured tibia model. A biphasic mechano-regulation algorithm is implemented to verify healing status under five different screw configurations (C1–C5) using glass/polypropylene composite bone plates and the development of tissue phenotypes in calluses is estimated. A 300% increase in circumferential callus volume is obtained when using the composite bone plate. Furthermore, the C5 configuration of the composite bone plate results in a maximum interfragmentary movement of 4.33% on day one with faster and stronger healing through 95% of bone growth during the final day of healing.

Finite element analysis of the impact of screw insertion distal to the trochanter minor on the risk of iatrogenic subtrochanteric fracture.

Iatrogenic subtrochanteric fractures are rarely encountered after cannulated screw fixation of femoral neck fractures; however, when they do occur, there can be several complications. Many orthopedic surgeons have concerns about the potential for iatrogenic subtrochanteric fractures after screw fixation distal to the trochanter minor; therefore, some surgeons are typically reluctant to perform this procedure. This study focused on the risk of an iatrogenic subtrochanteric fracture after treating femoral neck fractures with cannulated screws. The main purpose of the study was to understand iatrogenic subtrochanteric fractures and evaluate the effects on these fractures of an inverted triangular-shaped configuration for placement of the cannulated screws. A femur bone with an femoral neck fracture at a 40° incline to the horizontal plane was generated along with a representation of a three-dimensional finite element model, and three inverted triangular-shaped configurations for placement of the cannulated screws were investigated using finite element analyses. Statistical results indicated that the occurrence risk of ISF increases when the screw is located distal to the trochanter minor. Moreover, the risk of occurrence of intertrochanteric fracture increases when the screw is located medial to the trochanter minor because of local concentrated stress on the surface of the screw canals. To avoid the vulnerability of the subtrochanteric region, it was found that proximal placement of the screws using the inverted triangular-shaped configuration could yield better results. In addition, the results of this study provide suggestions on improved screw configurations.

Microwave Devulcanized Crumb Rubbers in Polypropylene Based Thermoplastic Dynamic Vulcanizates.

Because of the chemically crosslinked 3D molecular structure of rubbers, their recycling is a challenging task, especially when cost efficiency is also considered. One of the most straightforward procedures is the grinding of discarded rubber products with subsequent devulcanization. The devulcanized rubber can be used as a feedstock for fresh rubber compounds or can be blended with uncured virgin rubber and thermoplastic polymers to form thermoplastic dynamic vulcanizates (TDVs). TDVs combine the beneficial (re)processability of thermoplastics and the elastic properties of rubbers. Our current work focuses on the development of polypropylene (PP)-based TDVs with the use of a tire model rubber (MR) composed of natural rubber (NR) and styrene-butadiene rubber (SBR) in a ratio of 70/30. The research target was the partial substitution of the above fresh MR by microwave devulcanized crumb rubber (dCR). TDVs were produced by continuous extrusion, and the effects of composition (PP/MR/dCR = 40/60/0…50/35/15) and processing parameters (different screw configurations, temperature profiles, the feeding method of PP) were investigated. Results showed that the fresh rubber compound can be replaced up to 10 wt % without compromising the mechanical properties of the resulting TDV.

FACTORS AFFECTING THE FLOATING AQUATIC FEED PELLETS QUALITY

Production of high quality floating aquatic feed has in recent years accounted more than 65% of the market needs of fish feed. Most of fish feed factories have tended to develop their production lines by adding extrusion units to produce floating fish feed after increasing demand from farmers for this type of feed for many reasons, such as :the high conversion rates than sinking feed , decreased the consumed amounts of fish feed in aquaculture farms about 30%,easy to follow the fish vitality during feeding process and reduced the chances of infection by fish diseases. The parameters under studied were water addition site (just pre-conditioner- just extruder barrel zones -pre-conditioner and extruder barrel zones), extruder screw configurations profile (high configuration shear, medium configuration shear and low configuration shear) and drying cooling process after extrusion (cooling only and drying with cooling). Steam percentage of (13%) added into the pre-conditioner for all study treatments as constant parameters. The floating die specifications of the extruder were L/D ratio of 30:1, land length diameter of 2.5 mm and the die consists of 10 holes each outer diameter of 2.5mm. The optimum running parameters for proceeds floating aquatic feed were water addition into both pre-conditioner and extruder barrel zones (9%PC+5%EX), high shear screw configurations profile, and drying process for 10.5 min at air temperature of 210oC with cooling process for 5.5 min. The result of extruder performance and floating pellets quality measurements for these parameters were, extruder production rate of 196.6 kg/h, extruder specific mechanical energy (SME) of 130.7 kJ/kg, floating pellets bulk density of 332.9 kg/m3, final product pellets expansion ratio of 2.28, and floating pellets water stability of 100% after 33 h in water.

Obtuse triangle screw configuration for optimal internal fixation of femoral neck fracture: an anatomical analysis.

To identify the optimal screw configuration for internal fixation of femoral neck fractures based on anatomic analysis on radiologic imaging. 30 proximal femurs of 15 adults were constructed by CT. 3 femoral neck sections (FNS), the subcapital, medial, and the fundus, were projected on to the lateral femoral trochanteric wall. The simulated 3 screw configurations in the projection of FNS include: 2 inverted equilateral triangles symmetrised to the axis of the FNS (IET-FNS group) or the coronal axis of the proximal femur (IET-PR group) and an obtuse triangle (OT group). The distance between the screws, the distance between the centre of the FNS and the screws, and the area ratio of the triangle/FNS were calculated. The projection of the FNS on to the lateral femoral trochanteric wall is displayed as a rotating forward ellipse. Measurements of distance between screws, distance between the centre of the FNS to the screws, and the area ratio of triangle/FNS were significantly larger in the OT group than in the IET-FNS and IET-PF groups ( p < 0.05). The values of the 3 parameters in the IET-FNS group were also larger than those in the IET-PF group ( p < 0.05). The obtuse triangle screw configuration displayed advantages with respect to the parameters of distance between screws, distance between the centre of FNS to screws, and the triangle area. Therefore, the obtuse triangle screw configuration may be the ideal pattern for internal fixation of femoral neck fractures (Pauwels I and II). This needs to be corroborated with biomechanics testing.

Mathematical modeling for resource and energy saving control of extruders in multi-assortment productions of polymeric films

In this article, the authors describe mathematical modeling of polymer processing in extruders of various types used in extrusion and calender productions of film materials. The method consists of the synthesis of a static model for calculating throughput, energy consumption of the extruder, extrudate quality indices, as well as a dynamic model for evaluating polymer residence time in the extruder, on which the quality indices depend. Models are adjusted according to the extruder type (single-screw, reciprocating, twin-screw), its screw and head configuration, extruder’s work temperature conditions, and the processed polymer type. Models enable creating extruder screw configurations and determining extruder controlling action values that provide the extrudate of required quality while satisfying extruder throughput and energy consumption requirements. Model adequacy has been verified using polyolefins’ and polyvinylchloride processing data in different extruders. The program complex, based on mathematical models, has been developed in order to control extruders of various types in order to ensure resource and energy saving in multi-assortment productions of polymeric films. Using the program complex in the control system for the extrusion stage of the polymeric film productions enables improving film quality, reducing spoilage, lessening the time required for production line change-over to other throughput and film type assignment.

Arthroscopic Subtalar Arthrodesis: Does the Type of Fixation Modify Outcomes?

The goal of the present study was to analyze a modified American Orthopaedic Foot and Ankle Society (AOFAS) ankle-hindfoot scale score, time to union, and the incidence of fusion after isolated arthroscopic posterior subtalar arthrodesis using either 1 or 2 screws of different diameters. We reviewed a consecutive series of 65 patients, mean age 50.0 ± 15.6 years, including 38 males (58.5%) and 27 females (41.5%), who had undergone arthrodesis from May 2004 to February 2011. The mean follow-up duration was 57.5 (range 24 to 105) months. The patients were divided into 3 groups according to the fixation method used: group 1 (n = 12; 18.5%) underwent fixation with one 6.5-mm screw; group 2 (n = 40; 61.5%) with one 7.3-mm screw; and group 3 (n = 13; 20%) with two 7.3-mm screws. An overall statistically significant (p < .0001) improvement was seen in the modified AOFAS scale score for all 3 fixation groups; however, the difference was not statistically significant (p = .79) among the fixation groups. Fusion was achieved in 62 patients (95.4%) after a mean of 12.1 (range 9 to 16) weeks. The difference in the time to union was not statistically significant (p = .781) among the fixation groups. Nine patients (13.8%) experienced complications, and nonunion was significantly (p = .005) more prevalent in the single 6.5-mm screw group. In conclusion, all 3 screw configurations led to improved modified AOFAS scale scores, although nonunion was more common among patients fixed with a single 6.5-mm screw.

Evaluation of the role of carbon nanotubes on the electrical properties of poly(butylene terephthalate) nanocomposites for industrial applications

In this article, innovative electrically conductive polymer nanocomposites based on poly(butylene terephthalate) (PBT) filled with carbon nanotubes (CNTs) at different concentrations, to be used in the automotive field, have been investigated. Field emission scanning electron microscopy (FESEM) analysis revealed how a good nanofiller dispersion was obtained, especially by using surface treated nanotubes and by processing these materials using a more restrictive screw configuration. Melt flow index measurements highlighted that the processability of these nanocomposites was reduced at elevated filler amounts, even if CNT surface treatment promoted a partial retention of the fluidity of the neat PBT. Thermal degradation stability was improved upon the addition of CNT, even at limited filler amounts. Differential scanning calorimetry measurements evidenced how the presence of CNT slightly increased both the crystallization temperature and the crystalline fraction of the materials. The additivation of CNTs promoted a stiffening effect at elevated CNT contents, associated to an evident embrittlement of the samples. Electrical resistivity measurements showed that the most interesting results (i.e. 2.6 × 101 Ω·cm) were obtained for nanocomposites with a total filler content of 3 wt%, processed using the more restrictive screw configuration. For these materials, it was possible to obtain a rapid surface heating through Joule effect at applied voltages of 12 V.

Effects of chain-extending stabilizer on bioplastic poly(lactic acid)/polyamide blends compatibilized by reactive extrusion

The immiscible bio-plastic blend of poly(lactic acid) (PLA) and polyamide11 (PA11 or Nylon11) was compatibilized, using a catalyzed the ester-amide interchange chemical reaction during reactive extrusion. The effects of screw configuration on mixing and reaction optimization were explored. It was found that effective mixing and minimized degradation were achieved when kneading elements were installed only near the die end of the extruder rather than near the beginning of the melt section. However, significant degradation of PLA could not be avoided during processing, which led to a decrease in mechanical strength of blend. To prevent the molecular weight reduction, tris(nonylphenyl) phosphite (TNPP) stabilizer was introduced to improve the thermal stability of PLA matrix. Improvement to both tensile strength and elongation were achieved in the resulting PLA/PA11/TsOH/TNPP blend.

Biomechanical Strength of Retrograde Fixation in Proximal Third Scaphoid Fractures.

Background: Current techniques for fixation of proximal pole scaphoid fractures utilize antegrade fixation via a dorsal approach endangering the delicate vascular supply of the dorsal scaphoid. Volar and dorsal approaches demonstrate equivalent clinical outcomes in scaphoid wrist fractures, but no study has evaluated the biomechanical strength for fractures of the proximal pole. This study compares biomechanical strength of antegrade and retrograde fixation for fractures of the proximal pole of the scaphoid. Methods: A simulated proximal pole scaphoid fracture was produced in 22 matched cadaveric scaphoids, which were then assigned randomly to either antegrade or retrograde fixation with a cannulated headless compression screw. Cyclic loading and load to failure testing were performed and screw length, number of cycles, and maximum load sustained were recorded. Results: There were no significant differences in average screw length (25.5 mm vs 25.6 mm, P = .934), average number of cyclic loading cycles (3738 vs 3847, P = .552), average load to failure (348 N vs 371 N, P = .357), and number of catastrophic failures observed between the antegrade and retrograde fixation groups (3 in each). Practical equivalence between the 2 groups was calculated and the 2 groups were demonstrated to be practically equivalent (upper threshold P = .010). Conclusions: For this model of proximal pole scaphoid wrist fractures, antegrade and retrograde screw configuration have been proven to be equivalent in terms of biomechanical strength. With further clinical study, we hope surgeons will be able to make their decision for fixation technique based on approaches to bone grafting, concern for tenuous blood supply, and surgeon preference without fear of poor biomechanical properties.

Automatic Optimization of Screw Configuration of an Intermeshing Co-rotating Twin Screw Extruder using Artificial Intelligence Algorithm

Automatic Optimization of Screw Configuration of an Intermeshing Co-rotating Twin Screw Extruder using Artificial Intelligence Algorithm

Preparation, characterization, and pharmacokinetics in swine of a florfenicol enteric formulation prepared using hot-melt extrusion technology.

The objective of this work was to manufacture an enteric formulation of florfenicol (FF) using hot-melt extrusion (HME) technology and to evaluate its in vitro dissolution and in vivo pharmacokinetics. For the HME process, hypromellose acetate succinate LG (HPMCAS-LG) was the enteric polymer mixed with FF, and the two components were extruded with a standard screw configuration at a speed of 50rpm. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD), and Fourier transform infrared spectroscopy (FT-IR) were performed to characterize the HME extrudate. The release percentage of the enteric formulation in the acidic stage was <10% of the loaded FF, whereas that in the phosphate buffer stage was >80%. Pharmacokinetic evaluations in swine revealed that the enteric formulation had a longer t1/2λ and MRT than commercially available FF powder (FULAIKA® ), indicating that the novel formulation exhibited enteric and sustained release properties. Compared with the commercial product, the relative bioavailability of the enteric formulation reached up to 117.2%. This study suggests that this formulation may have potential for future commercialization.

Effects of Screw Configuration on the Preload Force of Implant-Abutment Screws.

The aim of this study was to investigate the effects of tightening torque, screw head angle, and thread number on the preload force of abutment screws. The test specimens consisted of three self-manufactured components (ie, a thread sleeve serving as an implant analog, an abutment analog, and an abutment screw). The abutment screws were fabricated with metric M1.6 external threads. The thread number varied between one and seven threads. The screw head angles were produced in eight varying angles (30 to 180 degrees). A sensor unit simultaneously measured the preload force of the screw and the torsion moment inside the screw shank. The tightening of the screw with the torque wrench was performed in five steps (15 to 35 Ncm). The torque wrench was calibrated before each step. Only the tightening torque and screw head angle affected the resulting preload force of the implant-abutment connection. The thread number had no effect. There was an approximately linear correlation between tightening torque and preload force. The tightening torque and screw head angle were the only study parameters that affected the resulting preload force of the abutment screw. The results obtained from this experiment are valid only for a single torque condition. Further investigations are needed that analyze other parameters that affect preload force. Once these parameters are known, it will add value for a strong, but detachable connection between the implant and abutment. Short implants and flat-to-flat connections especially will benefit significantly from this knowledge.

Assessment of spatial heterogeneity in continuous twin screw wet granulation process using three-compartmental population balance model

In this study, a novel three-compartmental population balance model (PBM) for a continuous twin screw wet granulation process is developed, combining the techniques of PBM and regression process modeling. The developed model links screw configuration, screw speed, and blend throughput with granule properties to predict the granule size distribution (GSD) and volume-average granule diameter. The granulator screw barrel was divided into three compartments along barrel length: wetting compartment, mixing compartment, and steady growth compartment. Different granulation mechanisms are assumed in each compartment. The proposed model therefore considers spatial heterogeneity, improving model prediction accuracy. An industrial data set containing 14 experiments is applied for model development. Three validation experiments show that the three-compartmental PBM can accurately predict granule diameter and size distribution at randomly selected operating conditions. Sixteen combinations of aggregation and breakage kernels are investigated in predicting the experimental GSD to best judge the granulation mechanism. The three-compartmental model is compared with a one-compartmental model in predicting granule diameter at different experimental conditions to demonstrate its advantage. The influence of the screw configuration, screw speed and blend throughput on the volume-average granule diameter is analyzed based on the developed model.

Does The Screw Orientation Effect s The Stability Of Femoral Neck Facture : A Finite Element Analysis

Objectives: The incidence of femoral neck fractures in younger-age people increases due to high-energy trauma. To avoid complications, stable internal fixation is essential. The most commonly used implants for vertically oriented femoral neck fractures are the cannulated and dynamic hip screws. In our study, we compared differently oriented cannulated screw configurations and a standard DHS for fixation of femoral neck fracture.Materials and Methods: A finite element-based collum femoris fracture was created and was fixed using four differently oriented triangular screw configurations and a dynamic hip screw. The loads were applied using a commercially available software package.Results: Centrally oriented cannulated screw configuration had the most compression and compression stress on the fracture side, and it had the highest stress values on the implant.Conclusion: We recommend the use of centrally oriented triangular cannulated screws for femoral neck fracture fixation. With this construct, more compression and compression pressure can be obtained, which can result in the early healing of the fracture. However, it must be kept in mind that this construct exerts more stress on the implant, which could be a reason for implant failure

Study of Sisal Fibre Attrition and Characterization during Direct Extrusion Compression Moulding

The Present Research work has been done under the sponsorship of Department of Science and Technology (DST), Government of India.Natural fibre reinforced thermoplastic composites getting higher demand in the present scenario. In this paper the research work has been done on Sisal fibre attrition and characterization during Direct Extrusion compression moulding. The continuous Sisal fibre rovings were obtained from external source and Physical properties were studied. Polypropylene was used as a matrix and Maleic Anhydride Polypropylene (MAPP) as a coupling agent. Fibre rovings were treated with 5% NaoH and Nacl (Alkaline and Silane) respectively to remove lignin content and impurities which were present in it and by that it was observed the improvement in fibre matrix adhesion. Extrusion process was achieved by introducing new compounding element and screw configuration by that fibre attrition has been reduced. Fibre length and Screw speed were considered as major parameters in characterization. Test plates were obtained for different volume fraction with different screw speeds. Obtained Test plates were tested as per ASTM standards in the mean time Solvent test and Microscopic tests were also conducted in order to do fibre length analysis. Increased Mechanical properties were obtained and it was correlated and validated with the fibre length and screw speed. From the results it was clear that the stiffness and dimension stability of the composites increases with the factors like fibre aspect ratio, volume fraction of fibres, fibre critical length and fibre to matrix modulus ratio.