Investigation on three-dimensional printed prosthetics leg sockets coated with different reinforcement materials: analysis on mechanical strength and microstructural.

Previous research has primarily focused on pre-processing parameters such as design, material selection, and printing techniques to improve the strength of 3D-printed prosthetic leg sockets. However, these methods fail to address the major challenges that arise post-printing, namely failures at the distal end of the socket and susceptibility to shear failure. Addressing this gap, the study aims to enhance the mechanical properties of 3D-printed prosthetic leg sockets through post-processing techniques. Fifteen PLA + prosthetic leg sockets are fabricated and reinforced with four materials: carbon fiber, carbon-Kevlar fiber, fiberglass, and cement. Mechanical and microstructural properties of the sockets are evaluated through axial compression testing and scanning electron microscopy (SEM). Results highlight superior attributes of cement-reinforced sockets, exhibiting significantly higher yield strength (up to 89.57% more than counterparts) and higher Young's modulus (up to 76.15% greater). SEM reveals correlations between microstructural properties and socket strength. These findings deepen the comprehension of 3D-printed prosthetic leg socket post-processing, presenting optimization prospects. Future research can focus on refining fabrication techniques, exploring alternative reinforcement materials, and investigating the long-term durability and functionality of post-processed 3D-printed prosthetic leg sockets.

Unilateral external fixator and its biomechanical effects in treating different types of femoral fracture: A finite element study with experimental validated model.

Previous works had successfully demonstrated the clinical effectiveness of unilateral external fixator in treating various types of fracture, ranging from the simple type, such as oblique and transverse fractures, to complex fractures. However, literature that investigated its biomechanical analyses to further justify its efficacy is limited. Therefore, this paper aimed to analyse the stability of unilateral external fixator for treating different types of fracture, including the simple oblique, AO32C3 comminuted, and 20 mm gap transverse fracture. These fractures were reconstructed at the distal diaphysis of the femoral bone and computationally analysed through the finite element method under the stance phase condition. Findings showed a decrease in the fixation stiffness in large gap fracture (645.2 Nmm-1 for oblique and comminuted, while 23.4 Nmm-1 for the gap fracture), which resulted in higher displacement, IFM and stress distribution at the pin bone interface. These unfavourable conditions could consequently increase the risk of delayed union, pin loosening and infection, as well as implant failure. Nevertheless, the stress observed on the fracture surfaces was relatively low and in controlled amount, indicating that bone unity is still allowable in all models. Briefly, the unilateral fixation may provide desirable results in smaller fracture gap, but its usage in larger gap fracture might be alarming. These findings could serve as a guide and insight for surgeons and researchers, especially on the biomechanical stability of fixation in different fracture types and how will it affect bone unity.

Biomechanical Effects of the Porous Structure of Gyroid and Voronoi Hip Implants: A Finite Element Analysis Using an Experimentally Validated Model.

Total hip arthroplasty (THA) is most likely one of the most successful surgical procedures in medicine. It is estimated that three in four patients live beyond the first post-operative year, so appropriate surgery is needed to alleviate an otherwise long-standing suboptimal functional level. However, research has shown that during a complete THA procedure, a solid hip implant inserted in the femur can damage the main arterial supply of the cortex and damage the medullary space, leading to cortical bone resorption. Therefore, this study aimed to design a porous hip implant with a focus on providing more space for better osteointegration, improving the medullary revascularisation and blood circulation of patients. Based on a review of the literature, a lightweight implant design was developed by applying topology optimisation and changing the materials of the implant. Gyroid and Voronoi lattice structures and a solid hip implant (as a control) were designed. In total, three designs of hip implants were constructed by using SolidWorks and nTopology software version 2.31. Point loads were applied at the x, y and z-axis to imitate the stance phase condition. The forces represented were x = 320 N, y = -170 N, and z = -2850 N. The materials that were used in this study were titanium alloys. All of the designs were then simulated by using Marc Mentat software version 2020 (MSC Software Corporation, Munich, Germany) via a finite element method. Analysis of the study on topology optimisation demonstrated that the Voronoi lattice structure yielded the lowest von Mises stress and displacement values, at 313.96 MPa and 1.50 mm, respectively, with titanium alloys as the materials. The results also indicate that porous hip implants have the potential to be implemented for hip implant replacement, whereby the mechanical integrity is still preserved. This result will not only help orthopaedic surgeons to justify the design choices, but could also provide new insights for future studies in biomechanics.

Thermal and mechanical characterization of composite materials from industrial plastic wastes and recycled nylon fibers for floor paving tiles application.

Industrial plastic waste is growing globally at an alarming rate and environmental pollution from traditional landfill disposal and incineration treatments are of great concern. As a strategy to reduce plastic pollution, value-added composite materials from industrial plastic wastes reinforced with recycled nylon fibers for use in floor paving tile applications were developed. This is to address the disadvantages of existing ceramic tiles which are relatively heavy, brittle, and expensive. The plastic waste composite structures were produced via compression molding technique at an optimized randomly oriented constant fiber volume fraction of 50 wt% after the initial sorting, cleaning, drying, pulverizing, and melt-mixing. The molding temperature, pressure, and time for the composite's structures were 220 ℃, 65 kg.cm-3, and 5 min respectively. The composites' thermal, mechanical, and microstructural properties were characterized in accordance with appropriate ASTM standards. From the results obtained, the differential scanning calorimetry (DSC) of mixed plastic wastes and nylon fiber wastes showed a processing temperature range of 130-180 ℃, and 250 ℃ respectively. Thermal degradation temperature (TGA) of the plastic and nylon fiber waste composites were stable above 400 ℃ with maximum bending strength, however, the reinforced plastic waste sandwiched composite structures had outstanding mechanical properties indicating unique characteristics suitable for floor paving tiles. Hence, the current research has developed tough and lightweight tiles composites that are economically viable, and their application will contribute to the development of the building and construction sectors thereby reducing about 10-15% of annual plastic waste generation and a sustainable environment.

Processing and properties optimisation of carbon nanofibre-reinforced magnesium composites for biomedical applications.

In the last decade, magnesium alloys have been considered as absorbable metals for biomedical applications, while some have reached their clinical use as temporary bone implants. However, their widespread use is still limited by its strength and degradability. One way of improvement can be done by reinforcing magnesium alloys with carbon nanofibres to form composites. This work aims at developing carbon nanofibre-reinforced magnesium-zinc (Mg-Zn/CNF) composites with optimum strength and degradability while ensuring their biocompatibility. A response surface method was used to determine their optimum process parameters (composition, compaction pressure, and sintering temperature), and analyse the resulting properties (elastic modulus, hardness, weight loss, and cytocompatibility). Results showed that the optimal parameters were reached at 1.8% of CNF, 425 MPa of compaction pressure, and 500 °C of sintering temperature, whereby it gave an elastic modulus of 5 GPa, hardness of 60 Hv, and a weight loss of 51% after three days immersion in PBS. The composites exhibited a hydrophobic surface that controlled the liberation of Mg2+ and Zn2+ ions, leading to more than 70% osteoblast cells viability up to seven days of incubation. This study can also serve as a starting point for future researchers interested in finding methods to fabricate Mg-Zn/CNF composites with high mechanical characteristics, corrosion resistance, and biocompatibility.

Effects of badminton insole design on stress distribution, displacement and bone rotation of ankle joint during single-leg landing: a finite element analysis.

Previous research has reported that up to 92% of injuries amongst badminton players consist of lower limb, whereby 35% of foot fractures occurred at the metatarsal bone. In sports, insoles are widely used to increase athletes' performance and prevent many injuries. However, there is still a lack of badminton insole analysis and improvements. Therefore, this study aimed to biomechanically analyse three different insole designs. A validated and converged three-dimensional (3D) finite element model of ankle-foot complex was developed, which consisted of the skin, talus, calcaneus, navicular, three cuneiform, cuboid, five metatarsals and five phalanges. Three existing insoles from the market, (1) Yonex Active Pro Truactive, (2) Victor VT-XD 8 and (3) Li-Ning L6200LA, were scanned using a 3D scanner. For the analysis, single-leg landing was simulated. On the superior surface of the skin, 2.57 times of the bodyweight was axially applied, and the inferior surface of the outsole was fixed. The results showed that Insole 3 was the most optimum design to reduce peak stress on the metatarsals (3.807 MPa). In conclusion, the optimum design of Insole 3, based on the finite element analysis, could be a justification of athletes' choices to prevent injury and other complications.

Biomechanical effects of cross-pin's diameter in reconstruction of anterior cruciate ligament - A specific case study via finite element analysis.

For anterior cruciate ligament reconstruction (ACL-R), one of the crucial aspects of treatment is the fixator selection that could provide initial graft fixation post-operatively. Literature on biomechanical stabilities of different sizes of fixators as femoral graft fixation is limited. Therefore, this study aims to analyse the influence of different diameters of cross-pins on the stability of graft fixations after ACL-R via finite element analysis (FEA). In the methodology, three-dimensional (3D) models of three different diameters of cross-pins were developed, of which anterior tibial loads (ATL) were applied onto the tibia. From the findings, the cross-pin with a smaller diameter (4 mm) provided optimum stability than larger diameter cross-pins, whereby it demonstrated acceptable stresses at the fixators (both cross-pin and interference screw) with a different percentage of 28%, while the stresses at the corresponding bones were favourable for osseointegration to occur. Besides, the strains of the knee joint with 4 mm diameter cross-pin were also superior in providing a good biomechanical environment for bone healing, while the recorded strain values at fixators were comparable with a larger diameter of cross-pins without being inferior in terms of deformation. To conclude, the cross-pin with 4 mm diameter depicted the best biomechanical aspects in graft fixation for ACL-R since it allows better assistance for the osseointegration process and can minimise the possibility of the breakage and migration of fixators. This study is not only useful for medical surgeons to justify their choices of pin diameter to treat patients, but also for researchers to conduct future studies.

Catalyst-Free Crosslinking Modification of Nata-de-Coco-Based Bacterial Cellulose Nanofibres Using Citric Acid for Biomedical Applications.

Bacterial cellulose (BC) has gained attention among researchers in materials science and bio-medicine due to its fascinating properties. However, BC's fibre collapse phenomenon (i.e., its inability to reabsorb water after dehydration) is one of the drawbacks that limit its potential. To overcome this, a catalyst-free thermal crosslinking reaction was employed to modify BC using citric acid (CA) without compromising its biocompatibility. FTIR, XRD, SEM/EDX, TGA, and tensile analysis were carried out to evaluate the properties of the modified BC (MBC). The results confirm the fibre crosslinking phenomenon and the improvement of some properties that could be advantageous for various applications. The modified nanofibre displayed an improved crystallinity and thermal stability with increased water absorption/swelling and tensile modulus. The MBC reported here can be used for wound dressings and tissue scaffolding.

Biomechanical analysis of three different types of fixators for anterior cruciate ligament reconstruction via finite element method: a patient-specific study.

Complication rates of anterior cruciate ligament reconstruction (ACL-R) were reported to be around 15% although it is a common arthroscopic procedure with good outcomes. Breakage and migration of fixators are still possible even months after surgery. A fixator with optimum stability can minimise those two complications. Factors that affect the stability of a fixator are its configuration, material, and design. Thus, this paper aims to analyse the biomechanical effects of different types of fixators (cross-pin, interference screw, and cortical button) towards the stability of the knee joint after ACL-R. In this study, finite element modelling and analyses of a knee joint attached with double semitendinosus graft and fixators were carried out. Mimics and 3-Matic softwares were used in the development of the knee joint models. Meanwhile, the graft and fixators were designed by using SolidWorks software. Once the meshes of all models were finished in 3-Matic, simulation of the configurations was done using MSC Marc Mentat software. A 100-N anterior tibial load was applied onto the tibia to simulate the anterior drawer test. Based on the findings, cross-pin was found to have optimum stability in terms of stress and strain at the femoral fixation site for better treatment of ACL-R.

The effects of additional hollow cylinder coated to external fixator screws for treating pilon fracture: A biomechanical perspective.

An external fixator is a promising medical device that could provide optimum stability and reduce the rate of complications in treating bone fracture during intervention period. It is noted that the biomechanics behaviour of device can be altered by introducing more features such as material suitability and additional components. Therefore, this study was conducted via finite element method to investigate the effects of additional hollow cylinder coated with external fixator screws in treating Type III pilon fracture. Finite element models which have been validated with experimental data were used to simulate stresses at the pin-bone interface and relative micromovement at interfragmentary fractures during swing (70 N load) and stance phases (350 N load). All bones and external fixators were assigned with isotropic material properties while the cartilages were simulated with hyper-elastic. For the hollow cylinder, polyethylene was assigned due to its properties which are equivalent to the bone. From the results, it is found that stresses at the pin-bone interface for the coated screws were reduced to 54% as compared to the conventional fixator. For the micromovement, there was no difference between both models, whereby the value was 0.03 mm. The results supported previously published literature, in which high stresses are unavoidable at the interface, fortunately, those stresses did not exceed the ultimate strength of bone, which is safe for treating patients. In conclusion, if patients are allowed to bear weight bearing, the external fixator with coated screws is a more favourable option to be fixed into the bone to avoid complications at the interface.

Biomechanical evaluation of three different configurations of external fixators for treating distal third tibia fracture: Finite element analysis in axial, bending and torsion load.

External fixators have been widely used in treating open fractures and have produced excellent outcomes, as they could successfully heal bones. The stability of external fixators lies greatly in their construction. Factors that associated with the stability of the external fixators includes stress, displacement, and relative micromotion. Three-dimensional (3D) models of bone and external fixators were constructed by using 3D modelling software, namely Materialise and SolidWorks, respectively. Three different configurations of external fixators namely Model 1, Model 2, and Model 3 were analysed. Three load cases were simulated to assess the abovementioned factors at the bone, specifically at the fracture site and at the external fixator. Findings showed that the double-cross configuration (Model 3) was the most promising in axial, bending, and torsion load cases as compared to the other two configurations. The no-cross configuration (Model 1) had the highest risk of complication due to high stress, relative micromotion, and displacement in the bending and torsion load cases. On the other hand, the single-cross configuration (Model 2) had the highest risk of complication when applied with axial load. In conclusion, the double-cross locking construct (Model 3) showed the biggest potential to be a new option for medical surgeons in treating patients associated with bone fracture. This new double-cross locking construct showed superior biomechanical stability as compared to single-cross and no-cross configurations in the axial, bending, and torsion load cases.

A finite element study: Finding the best configuration between unilateral, hybrid, and ilizarov in terms of biomechanical point of view.

In an open fracture, the external fixator is one of the definitive treatment options as it could provide the initial stabilisation of the fractured bone. Limited literature discussing on the biomechanical stability between unilateral, hybrid and Ilizarov configurations, principally in treating a femoral fracture. Thus, this study aims to analyse the biomechanical stability of different external fixators via the finite element method (FEM). The present study portrays that different configurations of fixators possess different biomechanical stability, hence leading to different healing rates and complication risks. For the methodology, three-dimensional models of three different external fixators were reconstructed where axial loads were applied on the proximal end of the femur, simulating the stance phase. From the results, the unilateral configuration provides better stability compared to the hybrid and Ilizarov, where it displaced the least with an average percentage difference of 50% for the fixator's frame and 23% for the bone. The unilateral configuration also produced the least interfragmentary movement (0.48 mm) as compared to hybrid (0.62 mm) and Ilizarov (0.61 mm) configurations. Besides, the strain and stress of the unilateral configuration were superior in terms of stability compared to the other two configurations. As a conclusion, the unilateral configuration had the best biomechanical stability as it was able to assist the bone healing process as well as minimising the risk of pin tract infection while treating a femoral fracture.

Stress Distributions and Micromovement of Fragment Bone of Pilon Fracture Treated With External Fixator: A Finite Element Analysis.

Osteoporosis and osteoarthritis are common pathological problems of the human bone tissue. There are some cases of pilon fractures associated with these 2 pathological conditions. In terms of treatment, for a normal and healthy bone with pilon fracture, the use of the Delta external fixator is a favorable option because it can allow early mobilization for patients and provide stability for the healing process. However, the stability of the external fixator differs when there is low bone stiffness, which has not been previously investigated. Therefore, this study was conducted to determine the stability of the external fixator to treat pilon fracture associated with osteoporosis and osteoarthritis, particularly to differentiate the stress distribution and micromovement of fracture fragment. Three-dimensional finite element models of the ankle and foot bones were reconstructed based on the computed tomography datasets. The bones consisted of 5 metatarsal, 3 cuneiform, and 1 each of cuboid, navicular, calcaneus, talus, fibula, and tibia bones. They were assigned with linear isotropic behavior. The ankle joint consisted of ligament and cartilage, and they were assigned with the use of linear links and the Mooney-Rivlin model, respectively. During simulation of the gait cycle, 70 N and 350 N were applied axially to the tibia bone to represent the swing and stance phases, respectively. The metatarsal and calcaneus bones were fixed to prevent any movement of the rigid body. The study found that the greatest von Mises stress value was observed at the pin-bone interface for the osteoporosis (108 MPa) model, followed by the osteoarthritis (87 MPa) and normal (44 MPa) models, during the stance phase. For micromovement, the osteoporosis model had the largest value at 0.26 mm, followed by the osteoarthritis (0.09 mm) and normal (0.03 mm) models. In conclusion, the greatest magnitudes of stress and micromovement were observed for the osteoporosis bone and extra care should be taken to treat pilon fracture associated with this pathological condition.

Development of Polymeric Nanocomposite (Xyloglucan-co-Methacrylic Acid/Hydroxyapatite/SiO2) Scaffold for Bone Tissue Engineering Applications-In-Vitro Antibacterial, Cytotoxicity and Cell Culture Evaluation.

Advancement and innovation in bone regeneration, specifically polymeric composite scaffolds, are of high significance for the treatment of bone defects. Xyloglucan (XG) is a polysaccharide biopolymer having a wide variety of regenerative tissue therapeutic applications due to its biocompatibility, in-vitro degradation and cytocompatibility. Current research is focused on the fabrication of polymeric bioactive scaffolds by freeze drying method for nanocomposite materials. The nanocomposite materials have been synthesized from free radical polymerization using n-SiO2 and n-HAp XG and Methacrylic acid (MAAc). Functional group analysis, crystallinity and surface morphology were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) techniques, respectively. These bioactive polymeric scaffolds presented interconnected and well-organized porous morphology, controlled precisely by substantial ratios of n-SiO2. The swelling analysis was also performed in different media at varying temperatures (27, 37 and 47 °C) and the mechanical behavior of the dried scaffolds is also investigated. Antibacterial activities of these scaffolds were conducted against pathogenic gram-positive and gram-negative bacteria. Besides, the biological behavior of these scaffolds was evaluated by the Neutral Red dye assay against the MC3T3-E1 cell line. The scaffolds showed interesting properties for bone tissue engineering, including porosity with substantial mechanical strength, biodegradability, biocompatibility and cytocompatibility behavior. The reported polymeric bioactive scaffolds can be aspirant biomaterials for bone tissue engineering to regenerate defecated bone.

Unifying the seeds auto-generation (SAGE) with knee cartilage segmentation framework: data from the osteoarthritis initiative.

PURPOSE: Manual segmentation is sensitive to operator bias, while semiautomatic random walks segmentation offers an intuitive approach to understand the user knowledge at the expense of large amount of user input. In this paper, we propose a novel random walks seed auto-generation (SAGE) hybrid model that is robust to interobserver error and intensive user intervention. METHODS: Knee image is first oversegmented to produce homogeneous superpixels. Then, a ranking model is developed to rank the superpixels according to their affinities to standard priors, wherein background superpixels would have lower ranking values. Finally, seed labels are generated on the background superpixel using Fuzzy C-Means method. RESULTS: SAGE has achieved better interobserver DSCs of 0.94 ± 0.029 and 0.93 ± 0.035 in healthy and OA knee segmentation, respectively. Good segmentation performance has been reported in femoral (Healthy: 0.94 ± 0.036 and OA: 0.93 ± 0.034), tibial (Healthy: 0.91 ± 0.079 and OA: 0.88 ± 0.095) and patellar (Healthy: 0.88 ± 0.10 and OA: 0.84 ± 0.094) cartilage segmentation. Besides, SAGE has demonstrated greater mean readers' time of 80 ± 19 s and 80 ± 27 s in healthy and OA knee segmentation, respectively. CONCLUSIONS: SAGE enhances the efficiency of segmentation process and attains satisfactory segmentation performance compared to manual and random walks segmentation. Future works should validate SAGE on progressive image data cohort using OA biomarkers.

Developing functionally graded PVA hydrogel using simple freeze-thaw method for artificial glenoid labrum.

Intact glenoid labrum is one of passive stabilizer for glenohumeral joint, which have various stiffness at different region. The aim of this study is to develop new artificial glenoid labrum from Polyvinyl Alcohol (PVA) hydrogel, which known as good biomaterial due to its biocompatibility and ability to tailor its modulus. PVA hydrogel was formed using freeze-thaw (FT) method and the stiffness of PVA was controlled by manipulating the concentration of PVA and number of FT cycles. Then, the gradual stiffness was formed using simple diffusion method by introducing the pre-freeze-and-thaw steps. The results showed 20% PVA with three FT cycles suit to highest stiffness of glenoid labrum while 10% PVA with three FT cycles suit to lowest stiffness of glenoid labrum. The functionally graded PVA hydrogel was then developed using the same method by diffusing two mixture (20% PVA and 10% PVA). Mechanical compression test showed, the highest modulus (0.41 MPa) found at the 20% PVA region and lowest modulus (0.1 MPa) found at 10% PVA region. While, at intermediate region, the compressive modulus was in between 20% and 10%, 0.2 MPa. The existence of gradual stiffness was further prove by checking crystallinity of material at each region using Differential Scanning Calorimetry (DSC) and Wide Angle X-ray Diffraction (WAXD). Microstructure of material was obtained from Scanning Electron Microscopy (SEM). This functionally graded PVA hydrogel also able to reduce about 51% of stress at glenoid implant and up to 17% for micromotion at the interfaces. Existence of artificial glenoid labrum could minimize the occurrence of glenoid component loosening.

Biomechanical features of six design of the delta external fixator for treating Pilon fracture: a finite element study.

Pilon fractures can be caused by high-energy vertical forces which may result in long-term patient immobilization. Many experts in orthopedic surgery recommend the use of a Delta external fixator for type III Pilon fracture treatment. This device can promote immediate healing of fractured bone, minimizing the rate of complications as well as allowing early mobilization. The characteristics of different types of the Delta frame have not been demonstrated yet. By using the finite element method, this study was conducted to determine the biomechanical characteristics of six different configurations (Model 1 until Model 6). CT images from the lower limb of a healthy human were used to reconstruct three-dimensional models of foot and ankle bones. All bones were assigned with isotropic material properties and the cartilages were assigned to exhibit hyperelasticity. A linear link was used to simulate 37 ligaments at the ankle joint. Axial loads of 70 and 350 N were applied at the proximal tibia to simulate the stance and swing phase. The metatarsals and calcaneus were fixed distally in order to prevent rigid body motion. A synthetic ankle bone was used to validate the finite element model. The simulated results showed that Delta3 produced the highest relative micromovement (0.09 mm, 7 µm) during the stance and swing phase, respectively. The highest equivalent von Mises stress was found at the calcaneus pin of the Delta4 (423.2 MPa) as compared to others. In conclusion, Delta1 external fixator was the most favorable option for type III Pilon fracture treatment. Graphical abstract ᅟ.

Finite element analysis of the wrist in stroke patients: the effects of hand grip.

The provision of the most suitable rehabilitation treatment for stroke patient remains an ongoing challenge for clinicians. Fully understanding the pathomechanics of the upper limb will allow doctors to assist patients with physiotherapy treatment that will aid in full arm recovery. A biomechanical study was therefore conducted using the finite element (FE) method. A three-dimensional (3D) model of the human wrist was reconstructed using computed tomography (CT)-scanned images. A stroke model was constructed based on pathological problems, i.e. bone density reductions, cartilage wane, and spasticity. The cartilages were reconstructed as per the articulation shapes in the joint, while the ligaments were modelled using linear links. The hand grip condition was mimicked, and the resulting biomechanical characteristics of the stroke and healthy models were compared. Due to the lower thickness of the cartilages, the stroke model reported a higher contact pressure (305 MPa), specifically at the MC1-trapezium. Contrarily, a healthy model reported a contact pressure of 228 MPa. In the context of wrist extension and displacement, the stroke model (0.68° and 5.54 mm, respectively) reported a lower magnitude than the healthy model (0.98° and 9.43 mm, respectively), which agrees with previously reported works. It was therefore concluded that clinicians should take extra care in rehabilitation treatment of wrist movement in order to prevent the occurrence of other complications. Graphical abstract ᅟ.

Biomechanical evaluation of two commonly used external fixators in the treatment of open subtalar dislocation--a finite element analysis.

Subtalar dislocation is a rare injury caused by high-energy trauma. Current treatment strategies include leg casts, internal fixation and external fixation. Among these, external fixators are the most commonly used as this method is believed to provide better stabilization. However, the biomechanical stability provided by these fixators has not been demonstrated. This biomechanical study compares two commonly used external fixators, i.e. Mitkovic and Delta. CT imaging data were used to reconstruct three-dimensional models of the tibia, fibula, talus, calcaneus, navicular, cuboid, three cuneiforms and five metatarsal bones. The 3D models of the bones and cartilages were then converted into four-noded linear tetrahedral elements, whilst the ligaments were modelled with linear spring elements. Bones and cartilage were idealized as homogeneous, isotropic and linear. To simulate loading during walking, axial loading (70 N during the swing and 350 N during the stance phase) was applied at the end of diaphyseal tibia. The results demonstrate that the Mitkovic fixator produced greater displacement (peak 3.0mm and 15.6mm) compared to the Delta fixator (peak 0.8mm and 3.9 mm), in both the swing and stance phase, respectively. This study demonstrates that the Delta external fixator provides superior stability over the Mitkovic fixator. The Delta fixator may be more effective in treating subtalar dislocation.

Finite element analysis of three commonly used external fixation devices for treating Type III pilon fractures.

Pilon fractures are commonly caused by high energy trauma and can result in long-term immobilization of patients. The use of an external fixator i.e. the (1) Delta, (2) Mitkovic or (3) Unilateral frame for treating type III pilon fractures is generally recommended by many experts owing to the stability provided by these constructs. This allows this type of fracture to heal quickly whilst permitting early mobilization. However, the stability of one fixator over the other has not been previously demonstrated. This study was conducted to determine the biomechanical stability of these external fixators in type III pilon fractures using finite element modelling. Three-dimensional models of the tibia, fibula, talus, calcaneus, navicular, cuboid, three cuneiforms and five metatarsal bones were reconstructed from previously obtained CT datasets. Bones were assigned with isotropic material properties, while the cartilage was assigned as hyperelastic springs with Mooney-Rivlin properties. Axial loads of 350 N and 70 N were applied at the tibia to simulate the stance and the swing phase of a gait cycle. To prevent rigid body motion, the calcaneus and metatarsals were fixed distally in all degrees of freedom. The results indicate that the model with the Delta frame produced the lowest relative micromovement (0.03 mm) compared to the Mitkovic (0.05 mm) and Unilateral (0.42 mm) fixators during the stance phase. The highest stress concentrations were found at the pin of the Unilateral external fixator (509.2 MPa) compared to the Mitkovic (286.0 MPa) and the Delta (266.7 MPa) frames. In conclusion, the Delta external fixator was found to be the most stable external fixator for treating type III pilon fractures.