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There is imminent refracture risk in elderly individuals for up to six years, with a decline thereafter except in women below 75 who face a constant elevated risk. Elderly men with fractures face the highest mortality risk, particularly those with hip and vertebral fractures. Targeted monitoring and treatment strategies are recommended. PURPOSE: Current management and interventions for osteoporotic fractures typically focus on bone mineral density loss, resulting in suboptimal evaluation of fracture risk. The aim of the study is to understand the progression of fractures to refractures and mortality in the elderly using multi-state models to better target those at risk. METHODS: This prospective, observational study analysed data from the AGES-Reykjavik cohort of Icelandic elderly, using multi-state models to analyse the evolution of fractures into refractures and mortality, and to estimate the probability of future events in subjects based on prognostic factors. RESULTS: At baseline, 4778 older individuals aged 65 years and older were included. Elderly men, and elderly women above 80 years of age, had a distinct imminent refracture risk that lasted between 2-6 years, followed by a sharp decline. However, elderly women below 75 continued to maintain a nearly constant refracture risk profile for ten years. Hip (30-63%) and vertebral (24-55%) fractures carried the highest 5-year mortality burden for elderly men and women, regardless of age, and for elderly men over 80, lower leg fractures also posed a significant mortality risk. CONCLUSION: The risk of refracture significantly increases in the first six years following the initial fracture. Elderly women, who experience fractures at a younger age, should be closely monitored to address their long-term elevated refracture risk. Elderly men, especially those with hip and vertebral fractures, face substantial mortality risk and require prioritized monitoring and treatment.
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Fraturas do Quadril , Fraturas por Osteoporose , Recidiva , Fraturas da Coluna Vertebral , Humanos , Fraturas por Osteoporose/mortalidade , Idoso , Masculino , Feminino , Islândia/epidemiologia , Idoso de 80 Anos ou mais , Fraturas do Quadril/mortalidade , Fraturas da Coluna Vertebral/mortalidade , Estudos Prospectivos , Medição de Risco/métodos , Progressão da Doença , Densidade Óssea/fisiologia , PrognósticoRESUMO
Cage subsidence after instrumented lumbar spinal fusion surgery remains a significant cause of treatment failure, specifically for posterior or transforaminal lumbar interbody fusion. Recent advancements in computational techniques and additive manufacturing, have enabled the development of patient-specific implants and implant optimization to specific functional targets. This study aimed to introduce a novel full-scale topology optimization formulation that takes the structural response of the adjacent bone structures into account in the optimization process. The formulation includes maximum and minimum principal strain constraints that lower strain concentrations in the adjacent vertebrae. This optimization approach resulted in anatomically and mechanically conforming spinal fusion cages. Subsidence risk was quantified in a commercial finite element solver for off-the-shelf, anatomically conforming and the optimized cages, in two representative patients. We demonstrated that the anatomically and mechanically conforming cages reduced subsidence risk by 91% compared to an off-the-shelf implant with the same footprint for a patient with normal bone quality and 54% for a patient with osteopenia. Prototypes of the optimized cage were additively manufactured and mechanically tested to evaluate the manufacturability and integrity of the design and to validate the finite element model.
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BACKGROUND AND OBJECTIVE: The accurate evaluation of bone mechanical properties is essential for predicting fracture risk based on clinical computed tomography (CT) images. However, blurring and noise in clinical CT images can compromise the accuracy of these predictions, leading to incorrect diagnoses. Although previous studies have explored enhancing trabecular bone CT images to super-resolution (SR), none of these studies have examined the possibility of using clinical CT images from different instruments, typically of lower resolution, as a basis for analysis. Additionally, previous studies rely on 2D SR images, which may not be sufficient for accurate mechanical property evaluation, due to the complex nature of the 3D trabecular bone structures. The objective of this study was to address these limitations. METHODS: A workflow was developed that utilizes convolutional neural networks to generate SR 3D models across different clinical CT instruments. The morphological and finite-element-derived mechanical properties of these SR models were compared with ground truth models obtained from micro-CT scans. RESULTS: A significant improvement in analysis accuracy was demonstrated, where the new SR models increased the accuracy by up to 700 % compared with the low-resolution data, i.e. clinical CT images. Additionally, we found that the mixture of different CT image datasets may improve the SR model performance. CONCLUSIONS: SR images, generated by convolutional neural networks, outperformed clinical CT images in the determination of morphological and mechanical properties. The developed workflow could be implemented for fracture risk prediction, potentially leading to improved diagnoses and subsequent clinical decision making.
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Processamento de Imagem Assistida por Computador , Redes Neurais de Computação , Processamento de Imagem Assistida por Computador/métodos , Tomografia Computadorizada por Raios X/métodos , Osso e Ossos , Osso EsponjosoRESUMO
A promising new treatment for large and complex bone defects is to implant specifically designed and additively manufactured synthetic bone scaffolds. Optimizing the scaffold design can potentially improve bone in-growth and prevent under- and over-loading of the adjacent tissue. This study aims to optimize synthetic bone scaffolds over multiple-length scales using the full-scale topology optimization approach, and to assess the effectiveness of this approach as an alternative to the currently used mono- and multi-scale optimization approaches for orthopaedic applications. We present a topology optimization formulation, which is matching the scaffold's mechanical properties to the surrounding tissue in compression. The scaffold's porous structure is tuneable to achieve the desired morphological properties to enhance bone in-growth. The proposed approach is demonstrated in-silico, using PEEK, cortical bone and titanium material properties in a 2D parameter study and on 3D designs. Full-scale topology optimization indicates a design improvement of 81% compared to the multi-scale approach. Furthermore, 3D designs for PEEK and titanium are additively manufactured to test the applicability of the method. With further development, the full-scale topology optimization approach is anticipated to offer a more effective alternative for optimizing orthopaedic structures compared to the currently used multi-scale methods.
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Alicerces Teciduais , Titânio , Alicerces Teciduais/química , Titânio/química , Osso e Ossos , Polímeros , PorosidadeRESUMO
Various femoral augmentation designs have been investigated over the past decade for the prevention of geriatric hip fracture. The experimental methods used to evaluate the efficacy of these augmentations have not been critically evaluated or compared in terms of biofidelity, robustness, or ease of application. Such parameters have significant relevance in characterizing future clinical success. In this study we aimed to use a scoping review to summarize the experimental studies that evaluate femoral augmentation approaches, and critically evaluate commonly applied protocols and identify areas for concordance with the clinical situation. We conducted a literature search targeting studies that used experimental test methods to evaluate femoral augmentation to prevent geriatric fragility fracture. A total of 25 studies met the eligibility criteria. The most commonly investigated augmentation to date is the injection of bone cement or another material that cured in situ, and a popular subsequent method for biomechanical evaluation was to load the augmented proximal femur until fracture in a sideways fall configuration. We noted limitations in the clinical relevance of sideways fall scenarios being modeled and large variance in the concordance of many of the studies identified. Our review brings about recommendations for enhancing the fidelity of experimental methods modeling clinical sideways falls, which include an improved representation of soft tissue effects, using outcome metrics beyond load-to-failure, and applying loads inertially. Effective augmentations are encouraging for their potential to reduce the burden of hip fracture; however, the likelihood of this success is only as strong as the methods used in their evaluation.
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Fraturas do Quadril , Ossos Pélvicos , Humanos , Idoso , Fêmur , Fraturas do Quadril/prevenção & controle , Fraturas do Quadril/cirurgia , Cimentos Ósseos/uso terapêutico , Fenômenos BiomecânicosRESUMO
Femoral fractures due to sideways falls continue to be a major cause of concern for the elderly. Existing approaches for the prevention of these injuries have limited efficacy. Prophylactic femoral augmentation systems, particularly those involving the injection of ceramic-based bone cements, are gaining more attention as a potential alternative preventative approach. We evaluated the mechanical effectiveness of three variations of a bone cement injection pattern (basic ellipsoid, hollow ellipsoid, small ellipsoid) utilizing finite element simulations of sideways fall impacts. The basic augmentation pattern was tested with both high- and low-strength ceramic-based cements. The cement patterns were added to the finite element models (FEMs) of five cadaveric femurs, which were then subject to simulated sideways falls at seven impact velocities ranging from 1.0 m/s to 4.0 m/s. Peak impact forces and peak acetabular forces were examined, and failure was evaluated using a strain-based criterion. We found that the basic HA ellipsoid provided the highest increases in both the force at the acetabulum of the impacted femur ("acetabular force", 55.0% ± 22.0%) and at the force plate ("impact force", 37.4% ± 15.8%). Changing the cement to a weaker material, brushite, resulted in reduced strengthening of the femur (45.2% ± 19.4% acetabular and 30.4% ± 13.0% impact). Using a hollow version of the ellipsoid appeared to have no effect on the fracture outcome and only a minor effect on the other metrics (54.1% ± 22.3% acetabular force increase and 35.3% ± 16.0% impact force increase). However, when the outer two layers of the ellipsoid were removed (small ellipsoid), the force increases that were achieved were only 9.8% ± 5.5% acetabular force and 8.2% ± 4.1% impact force. These results demonstrate the importance of supporting the femoral neck cortex to prevent femoral fractures in a sideways fall, and provide plausible options for prophylactic femoral augmentation. As this is a preliminary study, the surgical technique, the possible effects of trabecular bone damage during the augmentation process, and the effect on the blood supply to the femoral head must be assessed further.
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BACKGROUND: Ceramics are used in Total Disc Replacements (1) in articulating surfaces for their wear resistance and biocompatibility and (2) on endplates to promote osseointegration. They furthermore exhibit MRI and CT compatibility. These properties address main challenges associated with non-ceramic Total Disc Replacements i.e. wear, migration and postoperative imaging. While brittleness of ceramics caused fear of fracture in the past, improvements of ceramic materials were made and considerable clinical experience with ceramic Total Disc Replacements was gained. This review aims to assess the evidence on the use of ceramics in Total Disc Replacements and compare safety and effectiveness of ceramic Total Disc Replacements to spinal fusion and Total Disc Replacements in general. METHODS: We conducted a scoping review on the use of ceramics in Total Disc Replacements using Scopus, Web of Science and PubMed. The review includes 36 clinical, ex vivo and nonhuman in vivo, tribological and mechanical studies and case reports. FINDINGS: Ceramics are used in cervical Total Disc Replacements, with safety and efficacy confirmed in clinical studies, with up to 10 and 3.3 years follow-up, for articulation and osseointegration applications, respectively. Clinical evidence shows that ceramic Total Disc Replacements (alike non-ceramic ones) restore segmental motion and result in non-inferior and possibly superior outcomes to spinal fusion. In vivo studies show osseointegration comparable to non-ceramic devices. Tribological studies suggest appropriate wear properties. INTERPRETATION: We found no indications of systematic problems with the use of ceramics in Total Disc Replacements. Ceramics are suitable materials for Total Disc Replacements.
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Substituição Total de Disco , Humanos , Projetos de PesquisaRESUMO
Femoral fractures from sideways falls in the elderly are associated with significant rates of morbidity and mortality. Approaches to prevent these catastrophic injuries include pharmacological treatments, which have limited efficacy. Prophylactic femoral augmentation systems are a promising alternative that are gaining prominence by addressing the most debilitating osteoporosis-related fracture. We have developed finite element models (FEMs) of a novel experimental sideways fall simulator for cadavers. By virtue of the range of specimens and injury outcomes, these FEMs are well-suited to the evaluation of such implants. The purpose of this study was to use the FEMs to evaluate the mechanical effectiveness of three different prophylactic femoral augmentation systems. Models of the Y-Strut® (Hyprevention®, Pessac, France), Gamma Nail® (Stryker, Kalamazoo, USA), and a simple lag screw femoral fracture implant systems were placed into FEMs of five cadaveric pelvis-femur constructs embedded in a soft tissue surrogate, which were then subject to simulated sideways falls at seven impact velocities. Femur-only FEMs were also evaluated. Peak impact forces and peak acetabular forces were examined, and failure was evaluated using a strain-based criterion. We found that the femoral augmentation systems increased the peak forces prior to fracture, but were unable to prevent fracture for severe impacts. The Gamma Nail® system consistently produced the largest strength increases relative to the unaugmented femur for all five specimens in both the pendulum-drop FEMs and the femur-only simulations. In some cases, the same implant appeared to cause fractures in the acetabulum. The femur-only FEMs showed larger force increases than the pendulum-drop simulations, which suggests that the results of the femur-only simulations may not represent sideways falls as accurately as the soft tissue-embedded pendulum-drop simulations. The results from this study demonstrate the ability to simulate a high energy phenomenon and the effect of implants in an in silico environment. The results also suggest that implants could increase the force applied to the proximal femur during impact. Fracture outcomes from the tested implants can be used to inform the design of future devices, which reaffirms the value of modelling with biofidelic considerations in the implant design process. To the authors' knowledge, this is the first paper to use more complex biofidelic FEMs to assess prophylactic femoral augmentation methods.
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Fraturas do Quadril , Ossos Pélvicos , Idoso , Fêmur , Análise de Elementos Finitos , Fraturas do Quadril/prevenção & controle , HumanosRESUMO
Hip fractures in older adults, which often lead to lasting impairments and an increased risk of mortality, are a major public health concern. Hip fracture risk is multi-factorial, affected by the risk of falling, the load acting on the femur, and the load the femur can withstand. This study investigates the influence of impact direction on hip fracture risk and hip protector efficacy. We simulated falls for 4 subjects, in 7 different impact directions (15° and 30° anterior, lateral, and 15°, 30°, 60°, and 90° posterior) at two different impact velocities (2.1 and 3.1 m/s), all with and without hip protector, using previously validated biofidelic finite element models. We found the highest number of fractures and highest fragility ratios in lateral and 15° posterior impacts. The hip protector attenuated femur forces by 23-49 % for slim subjects under impact directions that resulted in fractures (30° anterior to 30° posterior). The hip protector prevented all fractures (6/6) for 2.1 m/s impacts, but only 10% of fractures for 3.1 m/s impacts. Our results provide evidence that, regarding hip fracture risk, posterior-lateral impacts are as dangerous as lateral impacts, and they support the efficacy of soft-shell hip protectors for anterior- and posterior-lateral impacts.
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Acidentes por Quedas/prevenção & controle , Fraturas do Quadril/prevenção & controle , Equipamentos de Proteção/normas , Fenômenos Biomecânicos , Simulação por Computador , Análise de Elementos Finitos , Humanos , Pressão , Estresse MecânicoRESUMO
Hip fractures associated with a high economic burden, loss of independence, and a high rate of post-fracture mortality, are a major health concern for modern societies. Areal bone mineral density is the current clinical metric of choice when assessing an individual's future risk of fracture. However, this metric has been shown to lack sensitivity and specificity in the targeted selection of individuals for preventive interventions. Although femoral strength derived from computed tomography based finite element models has been proposed as an alternative based on its superior femoral strength prediction ex vivo, such predictions have only shown marginal or no improvement for assessing hip fracture risk. This study compares finite element derived femoral strength to aBMD as a metric for hip fracture risk assessment in subjects (N = 601) from the AGES Reykjavik Study cohort and analyses the dependence of femoral strength predictions and classification accuracy on the material model and femoral loading alignment. We found hip fracture classification based on finite element derived femoral strength to be significantly improved compared to aBMD. Finite element models with non-linear material models performed better at classifying hip fractures compared to finite element models with linear material models and loading alignments with low internal rotation and adduction, which do not correspond to weak femur alignments, were found to be most suitable for hip fracture classification.
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Fraturas do Quadril , Ossos Pélvicos , Absorciometria de Fóton , Densidade Óssea , Fêmur/diagnóstico por imagem , Análise de Elementos Finitos , Fraturas do Quadril/epidemiologia , HumanosRESUMO
Muscle tissue composition accounting for the relative content of muscle fibers and intramuscular adipose and loose fibrous tissues can be efficiently analyzed and quantified using images from spiral computed tomography (S-CT) technology and the associated distribution of Hounsfield unit (HU) values. Muscle density distribution, especially when including the whole muscle volume, provides remarkable information on the muscle condition. Different physiological and pathological scenarios can be depicted using the muscle characterization technique based on the HU values and the definition of appropriate intervals and the association of such intervals to different colors. Using this method atrophy, degeneration, and restoration in denervated muscle undergoing electrical stimulation treatments can be clearly displayed and monitored. Moreover, finite element methods are employed to calculate Young's modulus on the patella bone and to analyze correlation between muscle contraction and bone strength changes. The reliability of this tool though depends on S-CT assessment and calibration. To assess imaging quality and the use of HU values to display muscle composition, different S-CT devices are compared using a Quasar body scanner. Density distributions and volumes of various calibration elements such as lung, polyethylene, water equivalent, and trabecular and dense bone are measured with different scanning protocols and at different points of time. The results show that every scanned element undergoes HU variations, which are greater for materials at the extremes of the HU scale, such as dense bone and lung inhale. Moreover, S-CT scanning with low tube voltages (80 KV) produces inaccurate HU values especially in bones. In conclusion, 3-D modeling techniques based on S-CT scanning is a powerful follow-up tool that may provide structural information at the millimeter scale, and thus may drive choice and timing to validate rehabilitation protocols.
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Osso e Ossos/diagnóstico por imagem , Terapia por Estimulação Elétrica , Imageamento Tridimensional/métodos , Músculos/diagnóstico por imagem , Traumatismos da Medula Espinal/diagnóstico por imagem , Tomografia Computadorizada por Raios X/métodos , Terapia por Estimulação Elétrica/métodos , Humanos , Traumatismos da Medula Espinal/terapiaRESUMO
BACKGROUND: Electrospun (ES) poly(É-caprolactone) (PCL) is widely used to provide critical mechanical support in tissue engineering and regenerative medicine applications. Therefore, there is a clear need for understanding the change in the mechanical response of the membranes as the material degrades in physiological conditions. STUDY DESIGN: ES membranes with fiber diameters from 1.6 to 6.7 µm were exposed to in vitro conditions at 37°C in Dulbecco's modified Eagle's medium (DMEM) or dry for up to 6 months. METHODS: During this period, the mechanical properties were assessed using cyclic mechanical loading, and material properties such as crystallinity and ester bond degradation were measured. RESULTS: No significant difference was found for any parameters between samples kept dry and in DMEM. The increase in crystallinity was linear with time, while the ester bond degradation showed an inverse logarithmic correlation with time. All samples showed an increase in modulus with exposure time for the first loading cycle. Modulus changes for the consecutive loading cycles showed a nonlinear relationship to the exposure time that depended on membrane type and maximum strain. In addition, the recovered elastic range showed an expected increase with the maximum strain reached. The mechanical response of ES membranes was compared to experimental tensile properties of the human annulus fibrosus tissue and an in silico model of the intervertebral disk. The modulus of the tested membranes was at the lower range of the values found in literature, while the elastically recoverable strain after preconditioning for all membrane types lies within the desired strain range for this application. CONCLUSION: The long-term assessment under application-specific conditions allowed to establish the mechanical competence of the electrospun PCL membranes. It can be concluded that with the use of appropriate fixation, the membranes can be used to create a seal on the damaged AF.
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PMMA bone cement has gained an important place in a variety of orthopaedic applications in the femur. However, appropriate data on the mechanical properties of bone-cement composites from the human femur are lacking. Therefore, the goal of this study was to determine the morphological and quasi-static compressive properties of proximal femoral bone-cement composites. Thirty trabecular bone specimens were extracted from fifteen pairs of human femoral heads using specimen-specific cutting guides to ensure an accurate alignment with the main trabecular direction (MTD). One specimen from each pair was augmented with PMMA bone cement, while the other one was left untreated. Specimens were scanned with µCT to determine morphological parameters and tested in quasi-static compression until failure. We found that the long axis of the specimens was highly aligned with the MTD (mean error < 5°). A higher compressive modulus and ultimate strength were observed for the bone-cement composite specimens (E = 5.7 ± 0.4 GPa; σu = 77.9 ± 5.1 MPa) compared to the bone only specimens (E = 2.9 ± 0.7 GPa; σu = 19.0 ± 5.8 MPa). Furthermore, the composites had a higher modulus, but lower strength than cement itself (E = 5.0 ± 0.3 GPa; σu = 85.9 ± 2.7 MPa) and the composite modulus was significantly correlated with the bone volume fraction (BV/TV). These results are in contrast to previous findings on human vertebral bone, where the composite was more compliant than cement and no correlation was found between BV/TV and the composite modulus. Thus, properties of bone-cement composites cannot simply be applied across different anatomical sites; the site-specific differences in bone density and trabecular alignment should be taken into account. Collectively, the present results suggest that at low BV/TV, cement dominates the composite properties, while at high BV/TV, the contribution of bone becomes apparent, revealing a positive relationship between BV/TV and the on-axis modulus.
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Cabeça do Fêmur , Polimetil Metacrilato , Cimentos Ósseos , Densidade Óssea , Força Compressiva , Cabeça do Fêmur/diagnóstico por imagem , Humanos , Coluna VertebralRESUMO
Computed tomography (CT)-derived finite element (FE) models have been proposed as a tool to improve the current clinical assessment of osteoporosis and personalized hip fracture risk by providing an accurate estimate of femoral strength. However, this solution has two main drawbacks, namely: (i) 3D CT images are needed, whereas 2D dual-energy x-ray absorptiometry (DXA) images are more generally available, and (ii) quasi-static femoral strength is predicted as a surrogate for fracture risk, instead of predicting whether a fall would result in a fracture or not. The aim of this study was to combine a biofidelic fall simulation technique, based on 3D computed tomography (CT) data with an algorithm that reconstructs 3D femoral shape and BMD distribution from a 2D DXA image. This approach was evaluated on 11 pelvis-femur constructs for which CT scans, ex vivo sideways fall impact experiments and CT-derived biofidelic FE models were available. Simulated DXA images were used to reconstruct the 3D shape and bone mineral density (BMD) distribution of the left femurs by registering a projection of a statistical shape and appearance model with a genetic optimization algorithm. The 2D-to-3D reconstructed femurs were meshed, and the resulting FE models inserted into a biofidelic FE modeling pipeline for simulating a sideways fall. The median 2D-to-3D reconstruction error was 1.02 mm for the shape and 0.06 g/cm3 for BMD for the 11 specimens. FE models derived from simulated DXAs predicted the outcome of the falls in terms of fracture versus non-fracture with the same accuracy as the CT-derived FE models. This study represents a milestone towards improved assessment of hip fracture risk based on widely available clinical DXA images.
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Fraturas do Quadril , Osteoporose , Absorciometria de Fóton , Densidade Óssea , Fêmur/diagnóstico por imagem , Análise de Elementos Finitos , Fraturas do Quadril/diagnóstico por imagem , HumanosRESUMO
INTRODUCTION: Ultimate strength-density relationships for bone have been reported with widely varying results. Reliable bone strength predictions are crucial for many applications that aim to assess bone failure. Bone density and bone morphology have been proposed to explain most of the variance in measured bone strength. If this holds true, it could lead to the derivation of a single ultimate strength-density-morphology relationship for all anatomical sites. METHODS: All relevant literature was reviewed. Ultimate strength-density relationships derived from mechanical testing of human bone tissue were included. The reported relationships were translated to ultimate strength-apparent density relationships and normalized with respect to strain rate. Results were grouped based on bone tissue type (cancellous or cortical), anatomical site, and loading mode (tension vs. compression). When possible, the relationships were compared to existing ultimate strength-density-morphology relationships. RESULTS: Relationships that considered bone density and morphology covered the full spectrum of eight-fold inter-study difference in reported compressive ultimate strength-density relationships for trabecular bone. This was true for studies that tested specimens in different loading direction and tissue from different anatomical sites. Sparse data was found for ultimate strength-density relationships in tension and for cortical bone properties transverse to the main loading axis of the bone. CONCLUSIONS: Ultimate strength-density-morphology relationships could explain measured strength across anatomical sites and loading directions. We recommend testing of bone specimens in other directions than along the main trabecular alignment and to include bone morphology in studies that investigate bone material properties. The lack of tensile strength data did not allow for drawing conclusions on ultimate strength-density-morphology relationships. Further studies are needed. Ideally, these studies would investigate both tensile and compressive strength-density relationships, including morphology, to close this gap and lead to more accurate evaluation of bone failure.
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Densidade Óssea , Osso e Ossos , Força Compressiva , Humanos , Estresse Mecânico , Resistência à TraçãoRESUMO
The structural integrity of cranial implants is of great clinical importance, as they aim to provide cerebral protection after neurosurgery or trauma. With the increased use of patient-specific implants, the mechanical response of each implant cannot be characterized experimentally in a practical way. However, computational models provide an excellent possibility for efficiently predicting the mechanical response of patient-specific implants. This study developed finite element models (FEMs) of titanium-reinforced calcium phosphate (CaP-Ti) implants. The models were validated with previously obtained experimental data for two different CaP-Ti implant designs (D1 and D2), in which generically shaped implant specimens were loaded in compression at either quasi-static (1 mm/min) or impact (5 kg, 1.52 m/s) loading rates. The FEMs showed agreement with experimental data in the force-displacement response for both implant designs. The implicit FEMs predicted the peak load with an underestimation for D1 (9%) and an overestimation for D2 (11%). Furthermore, the shape of the force-displacement curves were well predicted. In the explicit FEMs, the first part of the force-displacement response showed 5% difference for D1 and 2% difference for D2, with respect to the experimentally derived peak loads. The explicit FEMs efficiently predicted the maximum displacements with 1% and 4% difference for D1 and D2, respectively. Compared to the CaP-Ti implant, an average parietal cranial bone FEM showed a stiffer response, greater energy absorption and less deformation under the same impact conditions. The framework developed for modelling the CaP-Ti implants has a potential for modelling CaP materials in other composite implants in future studies since it only used literature based input and matched boundary conditions. Furthermore, the developed FEMs make an important contribution to future evaluations of patient-specific CaP-Ti cranial implant designs in various loading scenarios.
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Implantes Dentários , Titânio , Fosfatos de Cálcio , Análise de Elementos Finitos , Humanos , Próteses e Implantes , Crânio , Estresse MecânicoRESUMO
Cranial implants are used to repair bone defects following neurosurgery or trauma. At present, there is a lack of data on their mechanical response, particularly in impact loading. The aim of the present study was to assess the mechanical response of a recently developed composite calcium phosphate-titanium (CaP-Ti) implant at quasi-static and impact loading rates. Two different designs were tested, referred to as Design 1 (D1) and Design 2 (D2). The titanium structures in the implant specimens were additively manufactured by a powder-bed fusion process and subsequently embedded in a self-setting CaP material. D1 was conceptually representative of the clinically used implants. In D2, the titanium structure was simplified in terms of geometry in order to facilitate the manufacturing. The mechanical response of the implants was evaluated in quasi-static compression, and in impact using a drop-tower. Similar peak loads were obtained for the two designs, at the two loading rates: 808 ± 29 N and 852 ± 34 for D1, and 840 ± 40 N and 814 ± 13 for D2. A strain rate dependency was demonstrated for both designs, with a higher stiffness in the impact test. Furthermore, the titanium in the implant fractured in the quasi-static test (to failure) but not in the impact test (to 5.75 J) for D1. For D2, the displacement at peak load was significantly lower in the impact test than in the quasi-static test. The main difference between the designs was seen in the quasi-static test results where the deformation zones, i.e. notches in the titanium structure between the CaP tiles, in D1 likely resulted in a localization of the deformation, compared to in D2 (which did not have deformation zones). In the impact test, the only significant difference between the designs was a higher maximum displacement of D2 than of D1. In comparison with other reported mechanical tests on osteoconductive ceramic-based cranial implants, the CaP-Ti implant demonstrates the highest reported strength in quasi-static compression. In conclusion, the titanium structure seems to make the CaP-Ti implant capable of cerebral protection in impact situations like the one tested in this study.
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Próteses e Implantes , Titânio , Fosfatos de Cálcio , Teste de Materiais , CrânioRESUMO
The majority of hip fractures in the elderly are the result of a fall from standing or from a lower height. Current injury models focus mostly on femur strength while neglecting subject-specific loading. This article presents an injury modeling strategy for hip fractures related to sideways falls that takes subject-specific impact loading into account. Finite element models (FEMs) of the human body were used to predict the experienced load and the femoral strength in a single model. We validated these models for their predicted peak force, effective pelvic stiffness, and fracture status against matching ex vivo sideways fall impacts (n = 11) with a trochanter velocity of 3.1 m/s. Furthermore, they were compared to sideways impacts of volunteers with lower impact velocities that were previously conducted by other groups. Good agreement was found between the ex vivo experiments and the FEMs with respect to peak force (root mean square error [RMSE] = 10.7%, R2 = 0.85) and effective pelvic stiffness (R2 = 0.92, RMSE = 12.9%). The FEMs were predictive of the fracture status for 10 out of 11 specimens. Compared to the volunteer experiments from low height, the FEMs overestimated the peak force by 25% for low BMI subjects and 8% for high BMI subjects. The effective pelvic stiffness values that were derived from the FEMs were comparable to those derived from impacts with volunteers. The force attenuation from the impact surface to the femur ranged between 27% and 54% and was highly dependent on soft tissue thickness (R2 = 0.86). The energy balance in the FEMS showed that at the time of peak force 79% to 93% of the total energy is either kinetic or was transformed to soft tissue deformation. The presented FEMs allow for direct discrimination between fracture and nonfracture outcome for sideways falls and bridge the gap between impact testing with volunteers and impact conditions representative of real life falls. © 2019 American Society for Bone and Mineral Research.
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Acidentes por Quedas , Fraturas do Quadril , Modelos Biológicos , Estresse Mecânico , Idoso , Idoso de 80 Anos ou mais , Feminino , Análise de Elementos Finitos , Humanos , Cinética , Masculino , Pessoa de Meia-IdadeRESUMO
The risk of hip fracture of a patient due to a fall can be described from a mechanical perspective as the capacity of the femur to withstand the force that it experiences in the event of a fall. So far, impact forces acting on the lateral aspect of the pelvic region and femur strength have been investigated separately. This study used inertia-driven cadaveric impact experiments that mimic falls to the side from standing in order to evaluate the subject-specific force applied to the hip during impact and the fracture outcome in the same experimental model. Eleven fresh-frozen pelvis-femur constructs (6 female, 5 male, ageâ¯=â¯77â¯years (SDâ¯=â¯13â¯years), BMIâ¯=â¯22.8â¯kg/m2 (SDâ¯=â¯7.8â¯kg/m2), total hip aBMDâ¯=â¯0.734â¯g/cm2 (SDâ¯=â¯0.149â¯g/cm2)), were embedded into soft tissue surrogate material that matched subject-specific mass and body shape. The specimens were attached to metallic lower-limb constructions with subject-specific masses and subjected to an inverted pendulum motion. Impact forces were recorded with a 6-axis force plate at 10,000â¯Hz and three dimensional deflections in the pelvic region were tracked with two high-speed cameras at 5000â¯Hz. Of the 11 specimens, 5 femur fractures and 3 pelvis fractures were observed. Three specimens did not fracture. aBMD alone did not reliably separate femur fractures from non-fractures. However, a mechanical risk ratio, which was calculated as the impact force divided by aBMD, classified specimens reliably into femur fractures and non-fractures. Single degree of freedom models, based on specimen kinetics, were able to predict subject-specific peak impact forces (RMSEâ¯=â¯2.55% for non-fractures). This study provides direct evidence relating subject-specific impact forces and subject-specific strength estimates and improves the assessment of the mechanical risk of hip fracture for a specific femur/pelvis combination in a sideways fall.
Assuntos
Fraturas do Quadril/etiologia , Medição de Risco/métodos , Acidentes por Quedas/estatística & dados numéricos , Idoso , Idoso de 80 Anos ou mais , Autopsia , Feminino , Fraturas do Fêmur/epidemiologia , Fêmur/lesões , Análise de Elementos Finitos , Fraturas do Quadril/epidemiologia , Humanos , Masculino , Pessoa de Meia-Idade , Ossos Pélvicos/lesões , Estresse MecânicoRESUMO
Pushout tests can be used to estimate the shear strength of the bone implant interface. Numerous such experimental studies have been published in the literature. Despite this researchers are still some way off with respect to the development of accurate numerical models to simulate implant stability. In the present work a specific experimental pushout study from the literature was simulated using two different bones implant interface models. The implant was a porous coated Ti-6Al-4V retrieved 4 weeks postoperatively from a dog model. The purpose was to find out which of the interface models could replicate the experimental results using physically meaningful input parameters. The results showed that a model based on partial bone ingrowth (ingrowth stability) is superior to an interface model based on friction and prestressing due to press fit (initial stability). Even though the present study is limited to a single experimental setup, the authors suggest that the presented methodology can be used to investigate implant stability from other experimental pushout models. This would eventually enhance the much needed understanding of the mechanical response of the bone implant interface and help to quantify how implant stability evolves with time.