Computational models of bone fracture healing and applications: a review.

Fracture healing is a very complex physiological process involving multiple events at different temporal and spatial scales, such as cell migration and tissue differentiation, in which mechanical stimuli and biochemical factors assume key roles. With the continuous improvement of computer technology in recent years, computer models have provided excellent solutions for studying the complex process of bone healing. These models not only provide profound insights into the mechanisms of fracture healing, but also have important implications for clinical treatment strategies. In this review, we first provide an overview of research in the field of computational models of fracture healing based on CiteSpace software, followed by a summary of recent advances, and a discussion of the limitations of these models and future directions for improvement. Finally, we provide a systematic summary of the application of computational models of fracture healing in three areas: bone tissue engineering, fixator optimization and clinical treatment strategies. The application of computational models of bone healing in clinical treatment is immature, but an inevitable trend, and as these models become more refined, their role in guiding clinical treatment will become more prominent.

mResU-Net: multi-scale residual U-Net-based brain tumor segmentation from multimodal MRI.

Brain tumor segmentation is an important direction in medical image processing, and its main goal is to accurately mark the tumor part in brain MRI. This study proposes a brand new end-to-end model for brain tumor segmentation, which is a multi-scale deep residual convolutional neural network called mResU-Net. The semantic gap between the encoder and decoder is bridged by using skip connections in the U-Net structure. The residual structure is used to alleviate the vanishing gradient problem during training and ensure sufficient information in deep networks. On this basis, multi-scale convolution kernels are used to improve the segmentation accuracy of targets of different sizes. At the same time, we also integrate channel attention modules into the network to improve its accuracy. The proposed model has an average dice score of 0.9289, 0.9277, and 0.8965 for tumor core (TC), whole tumor (WT), and enhanced tumor (ET) on the BraTS 2021 dataset, respectively. Comparing the segmentation results of this method with existing techniques shows that mResU-Net can significantly improve the segmentation performance of brain tumor subregions.

Improved adaptive tessellation rendering algorithm.

BACKGROUND: The human body model in the virtual surgery system is generally nested by multiple complex models and each model has quite complex tangent and curvature change. In actual rendering, if all details of the human body model are rendered with high performance, it may cause the stutter due to insufficient hardware performance. If the human body model is roughly rendered, the details of the model cannot be well represented. OBJECTIVE: In order to realize the real-time rendering of complex models in virtual surgical systems, this paper proposes an improved adaptive tessellation rendering algorithm, which includes offline and online parts. METHODS: The offline part mainly completes data reading and data structure constructing. The online part performs the surface subdivision operation in-real time for each frame, which includes the subdivision operation of the control points and surface evaluation. The offline part simplifies the subdivision step by recording the surface subdivision hierarchy using a quadtree and using control templates to record control point information. RESULTS: The online part reduces computation time by using a matrix to record topological relationships between vertices and vertex weights. The online part can compress the time complexity of traversing the quadtree of different subdivision levels to O⁢(n⁢log⁡n) by establishing an association with the quadtree of each subdivision level and using the greedy algorithm to complete the traversal of the quadtree. Finally, the adaptive tessellation rendering algorithm proposed in this paper is compared with other commonly used tessellation algorithms. CONCLUSION: The algorithm has advantages in computational efficiency and graphical display.

An Automatic Segmentation Method for Lung Tumor Based on Improved Region Growing Algorithm.

In medical image processing, accurate segmentation of lung tumors is very important. Computer-aided accurate segmentation can effectively assist doctors in surgery planning and treatment decisions. Although the accurate segmentation results of lung tumors can provide a reliable basis for clinical treatment, the key to obtaining accurate segmentation results is how to improve the segmentation performance of the algorithm. We propose an automatic segmentation method for lung tumors based on an improved region growing algorithm, which uses the prior information on lung tumors to achieve an automatic selection of the initial seed point. The proposed method includes a seed point expansion mechanism and an automatic threshold update mechanism and takes the combination of multiple segmentation results as the final segmentation result. In the lung image database consortium (LIDC-IDRI) dataset, we designed 10 experiments to test the proposed method and compare it with 4 popular segmentation methods. The experimental results show that the average dice coefficient obtained by the proposed method is 0.936 ± 0.027, and the average Jaccard distance is 0.114 ± 0.049. The average dice coefficient obtained by the proposed method is 0.107, 0.053, 0.040, and 0.156, higher than that of the other four methods, respectively. This study proves that the proposed method can automatically segment lung tumors in CT slices and has suitable segmentation performance.

A novel virtual cutting method for deformable objects using high-order elements combined with mesh optimisation.

BACKGROUND: Virtual cutting of deformable objects plays an important role in many applications, especially in digital medicine, such as soft tissue cutting in virtual surgery training system. METHODS: We developed a novel virtual cutting algorithm, combined with mesh optimisation. A new local mesh processing method is used to control the number and quality of the elements created during the cutting process. At the same time, high-order tetrahedral elements are used to fit the cutting surface and reduce the mesh size. RESULTS: In this paper, single cut, multiple cut and intersecting cut are performed on the mesh model, combined with a force feedback device, and the result obtained is that the visual feedback is higher than 30 Hz, and the tactile feedback is 800∼1000 Hz. CONCLUSIONS: Experimental results show that the method proposed in this paper can effectively eliminate low-quality elements and control the mesh size, thereby ensuring real-time simulation.

Multiscale modeling of skeletal muscle to explore its passive mechanical properties and experiments verification.

The research of the mechanical properties of skeletal muscle has never stopped, whether in experimental tests or simulations of passive mechanical properties. To investigate the effect of biomechanical properties of micro-components and geometric structure of muscle fibers on macroscopic mechanical behavior, in this manuscript, we establish a multiscale model where constitutive models are proposed for fibers and the extracellular matrix, respectively. Besides, based on the assumption that the fiber cross-section can be expressed by Voronoi polygons, we optimize the Voronoi polygons as curved-edge Voronoi polygons to compare the effects of the two cross-sections on macroscopic mechanical properties. Finally, the macroscopic stress response is obtained through the numerical homogenization method. To verify the effectiveness of the multi-scale model, we measure the mechanical response of skeletal muscles in the in-plane shear, longitudinal shear, and tensions, including along the fiber direction and perpendicular to the fiber direction. Compared with experimental data, the simulation results show that this multiscale framework predicts both the tension response and the shear response of skeletal muscle accurately. The root mean squared error (RMSE) is 0.0035 MPa in the tension along the fiber direction; The RMSE is 0.011254 MPa in the tension perpendicular to the fiber direction; The RMSE is 0.000602 MPa in the in-plane shear; The RMSE was 0.00085 MPa in the longitudinal shear. Finally, we obtained the influence of the component constitutive model and muscle fiber cross-section on the macroscopic mechanical behavior of skeletal muscle. In terms of the tension perpendicular to the fiber direction, the curved-edge Voronoi polygons achieve the result closer to the experimental data than the Voronoi polygons. Skeletal muscle mechanics experiments verify the effectiveness of our multiscale model. The comparison results of experiments and simulations prove that our model can accurately capture the tension and shear behavior of skeletal muscle.

An efficient method to improve the quality of tetrahedron mesh with MFRC.

In this paper, we proposed a novel operation to reconstruction tetrahedrons within a certain region, which we call MFRC (Multi-face reconstruction). During the existing tetrahedral mesh improvement methods, the flip operation is one of the very important components. However, due to the limited area affected by the flip, the improvement of the mesh quality by the flip operation is also very limited. The proposed MFRC algorithm solves this problem. MFRC can reconstruct the local mesh in a larger range and can find the optimal tetrahedron division in the target area within acceptable time complexity. Therefore, based on the MFRC algorithm, we combined other operations including smoothing, edge removal, face removal, and vertex insertion/deletion to develop an effective mesh quality improvement method. Numerical experiments of dozens of meshes show that the algorithm can effectively improve the low-quality elements in the tetrahedral mesh, and can effectively reduce the running time, which has important significance for the quality improvement of large-scale mesh.

A review of computer-assisted orthopaedic surgery systems.

BACKGROUND: Computer-assisted orthopaedic surgery systems have great potential, but no review has focused on computer-assisted surgery systems for the spine, hip, and knee. METHODS: A systematic search was performed in Web of Science and PubMed. We searched the literature on computer-assisted orthopaedic surgery systems from 2008 to the present and focused on three aspects of systems: training, planning, and intraoperative navigation. RESULTS AND DISCUSSION: In this review study, we reviewed 34 surgical training systems, 31 surgical planning systems, and 41 surgical navigation systems. The functions and characteristics of the surgical systems were compared and analysed, and the current concerns about and the impact of the surgical systems on doctors and surgery were clarified. CONCLUSION: Computer-assisted orthopaedic surgery systems are still in the development stage. Future surgical training systems should include synthetic models with patient anatomy. Surgical planning systems with automatic planning should be developed, and surgical navigation systems with multimodal fusion, robotic assistance and imaging should be developed.

Modeling and simulation of excitation- contraction coupling of fast-twitch skeletal muscle fibers.

BACKGROUND: The current excitation-contraction coupling model of fast-twitch skeletal muscle fibers cannot completely simulate the excitation-contraction process. OBJECTIVE: To solve this problem, this study proposes an excitation-contraction model of fast-twitch skeletal muscle fibers based on the physiological structure and contractile properties of half-sarcomeres. METHODS: The model includes the action potential model of fast-twitch fiber membranes and transverse tubule membranes, the cycle model of 𝐶𝑎2+ in myofibril, the cross-bridge cycle model, and the fatigue model of metabolism. RESULTS: Finally, detailed analyses of the results from the simulation are conducted using the Simulink toolbox in MATLAB. Two conditions, non-coincidence and coincidence, are analyzed for both the thick and thin myofilaments. CONCLUSIONS: The simulation results of two groups of models are the same as the previous research results, which validates the accuracy of models.

Label fusion method combining pixel greyscale probability for brain MR segmentation.

Multi-atlas-based segmentation (MAS) methods have demonstrated superior performance in the field of automatic image segmentation, and label fusion is an important part of MAS methods. In this paper, we propose a label fusion method that incorporates pixel greyscale probability information. The proposed method combines the advantages of label fusion methods based on sparse representation (SRLF) and weighted voting methods using patch similarity weights (PSWV) and introduces pixel greyscale probability information to improve the segmentation accuracy. We apply the proposed method to the segmentation of deep brain tissues in challenging 3D brain MR images from publicly available IBSR datasets, including images of the thalamus, hippocampus, caudate, putamen, pallidum and amygdala. The experimental results show that the proposed method has higher segmentation accuracy and robustness than the related methods. Compared with the state-of-the-art methods, the proposed method obtains the best putamen, pallidum and amygdala segmentation results and hippocampus and caudate segmentation results that are similar to those of the comparison methods.

Mechanical Respond and Failure Mode of Large Size Honeycomb Sandwiched Composites under In-Plane Shear Load.

The present work focuses on the in-plane shear respond and failure mode of large size honeycomb sandwich composites which consist of plain weave carbon fabric laminate skins and aramid paper core. A special size specimen based on a typical element of aircraft fuselage was designed and manufactured. A modified in-plane shear test method and the corresponding fixture was developed. Three large size specimens were tested. The distributed strain gauges were used to monitor the mechanical response and ultimate bearing capacity. The results show that a linear respond of displacement and strain appears with the increase of the load. The average shear failure load reaches 205.68 kN with the shear failure occurring on the face sheet, and the maximum shear strain monitored on the composite plate is up to 16,115 µÎµ. A combination of theoretical analysis and finite element method (FEM) was conducted to predict the shear field distribution and the overall buckling load. The out-of-plane displacement field distribution and in-plane shear strain field distribution under the pure shear loading were revealed. The theoretical analysis method was deduced to obtain the variation rule of the shear buckling load. A good agreement was achieved among the experiment, theoretical analysis, and FEM results. It can be concluded that the theoretical analysis method is relatively conservative, and the FEM is more accurate in case of deformation and strain. The results predicted by h element and p element methods are very close. The results of the study could provide data support for the comprehensive promotion of the design and application of honeycomb sandwich composites.

Multi-atlas active contour segmentation method using template optimization algorithm.

BACKGROUND: Brain image segmentation is the basis and key to brain disease diagnosis, treatment planning and tissue 3D reconstruction. The accuracy of segmentation directly affects the therapeutic effect. Manual segmentation of these images is time-consuming and subjective. Therefore, it is important to research semi-automatic and automatic image segmentation methods. In this paper, we propose a semi-automatic image segmentation method combined with a multi-atlas registration method and an active contour model (ACM). METHOD: We propose a multi-atlas active contour segmentation method using a template optimization algorithm. First, a multi-atlas registration method is used to obtain the prior shape information of the target tissue, and then a label fusion algorithm is used to generate the initial template. Second, a template optimization algorithm is used to reduce the multi-atlas registration errors and generate the initial active contour (IAC). Finally, a ACM is used to segment the target tissue. RESULTS: The proposed method was applied to the challenging publicly available MR datasets IBSR and MRBrainS13. In the MRBrainS13 datasets, we obtained an average thalamus Dice similarity coefficient of 0.927 ± 0.014 and an average Hausdorff distance (HD) of 2.92 ± 0.53. In the IBSR datasets, we obtained a white matter (WM) average Dice similarity coefficient of 0.827 ± 0.04 and a gray gray matter (GM) average Dice similarity coefficient of 0.853 ± 0.03. CONCLUSION: In this paper, we propose a semi-automatic brain image segmentation method. The main contributions of this paper are as follows: 1) Our method uses a multi-atlas registration method based on affine transformation, which effectively reduces the multi-atlas registration time compared to the complex nonlinear registration method. The average registration time of each target image in the IBSR datasets is 255 s, and the average registration time of each target image in the MRBrainS13 datasets is 409 s. 2) We used a template optimization algorithm to improve registration error and generate a continuous IAC. 3) Finally, we used a ACM to segment the target tissue and obtain a smooth continuous target contour.

A review of virtual cutting methods and technology in deformable objects.

BACKGROUND: Virtual cutting of deformable objects has been a research topic for more than a decade and has been used in many areas, especially in surgery simulation. METHODS: We refer to the relevant literature and briefly describe the related research. The virtual cutting method is introduced, and we discuss the benefits and limitations of these methods and explore possible research directions. RESULTS: Virtual cutting is a category of object deformation. It needs to represent the deformation of models in real time as accurately, robustly and efficiently as possible. To accurately represent models, the method must be able to: (1) model objects with different material properties; (2) handle collision detection and collision response; and (3) update the geometry and topology of the deformable model that is caused by cutting. CONCLUSION: Virtual cutting is widely used in surgery simulation, and research of the cutting method is important to the development of surgery simulation.

Three-dimensional computational model simulating the fracture healing process with both biphasic poroelastic finite element analysis and fuzzy logic control.

A dynamic model regulated by both biphasic poroelastic finite element analysis and fuzzy logic control was established. Fuzzy logic control was an easy and comprehensive way to simulate the tissue differentiation process, and it is convenient for researchers and medical experts to communicate with one another to change the fuzzy logic rules and improve the simulation of the tissue differentiation process. In this study, a three-dimensional fracture healing model with two different interfragmentary movements (case A: 0.25 mm and case B: 1.25 mm) was analysed with the new set-up computational model. As the healing process proceeded, both simulated interfragmentary movements predicted a decrease and the time that the decrease started for case B was later than that for case A. Compared with experimental results, both cases corresponded with experimental data well. The newly established dynamic model can simulate the healing process under different mechanical environments and has the potential to extend to the multiscale healing model, which is essential for reducing the animal experiments and helping to characterise the complex dynamic interaction between tissue differentiations within the callus region.

Development and application of computer assisted optimal method for treatment of femoral neck fracture.

BACKGROUND: To help doctors decide their treatment from the aspect of mechanical analysis, the work built a computer assisted optimal system for treatment of femoral neck fracture oriented to clinical application. OBJECTIVE: The whole system encompassed the following three parts: Preprocessing module, finite element mechanical analysis module, post processing module. METHODS: Preprocessing module included parametric modeling of bone, parametric modeling of fracture face, parametric modeling of fixed screw and fixed position and input and transmission of model parameters. Finite element mechanical analysis module included grid division, element type setting, material property setting, contact setting, constraint and load setting, analysis method setting and batch processing operation. Post processing module included extraction and display of batch processing operation results, image generation of batch processing operation, optimal program operation and optimal result display. RESULTS: The system implemented the whole operations from input of fracture parameters to output of the optimal fixed plan according to specific patient real fracture parameter and optimal rules, which demonstrated the effectiveness of the system. CONCLUSIONS: Meanwhile, the system had a friendly interface, simple operation and could improve the system function quickly through modifying single module.

High-quality mesh generation for human hip based on ideal element size: methods and evaluation.

The objective of this work was to obtain high-quality mesh generation results for the human hip. This study adopted an edge-collapse algorithm based on quadric error metrics to simplify the hip model. The adjacent triangular areas and a cost function that considered the mean value of error were introduced to avoid error accumulation and ensure invariant geometric features. Local mesh refinement was achieved by constructing a comprehensive size field. Finally, high-quality surface and volume meshes were generated using the advancing-front technique (AFT) and Delaunay algorithms. Two human hipbones, 13 muscles, and one articular cartilage sample were modelled. The hip model was simplified and the mesh was generated using the method proposed in this study. The smallest angle of most surface mesh elements was greater than 45°, and the triangular numbers in this optimal angle interval were superior to those generated by the AFT algorithms. Eight quality evaluation parameters of the mesh model were tested using the check-elems tool. The femoral meshing results in this work were more accurate than those obtained with the AFT algorithms. The results of the vastus lateralis mesh generation were superior to the results obtained with the existing algorithm, except for the volume skew parameter. The proportions for the high-quality tetrahedral elements obtained using Wang's algorithm for the femur and the vastuslateralis muscle were 17.81% and 24.50%, respectively. The proportions obtained using the hypermesh software were 16.31% and 22.87% for the femoral and vastuslateralis models, respectively. The proposed method had better adaptability to the complex model. The generated mesh was uniform and contained smooth transitions. The mesh generation result was similar to the original geometric model, which made the assembly model fit more accurately. This was significant for the convergence of the finite-element analysis program.

A review of computational models of bone fracture healing.

In the process of fracture healing, there are many cellular and molecular events that are regulated by mechanical stimuli and biochemical signals. To explore the unknown mechanisms underlying bone fracture healing, optimal fixation configurations, and the design of new treatment strategies, computational healing models provide a good solution. With the simulation of mechanoregulatory healing models, bioregulatory healing models and coupled mechanobioregulatory healing models, healing outcomes can be predicted. In this review, first, we provide an overview of current computational healing models. Their clinical applications are also presented. Then, the limitations of current models and their corresponding solutions are discussed in this review. Finally, future potentials are presented in this review. Multiscale modeling from the intracellular level to the tissue level is essential, and more clinical applications of computational healing models are required in future research.

A review of bioregulatory and coupled mechanobioregulatory mathematical models for secondary fracture healing.

Fracture healing is a complex biological process involving many cellular and molecular events. During fracture healing, biochemical signals play a regulatory role in promoting the healing process. Although many experiments have been conducted to study fracture healing, not all of the mechanisms are clearly understood. Over the past years, a lot of mathematical models and computational simulations have been established to investigate the fracture healing process. These models offer a powerful tool to study the interplay between cell behaviour, mechanical stimuli and biochemical signals and help design new treatment strategies. However, most of the mathematical models focus on the effect of mechanical stimuli and few models consider the important role of biochemical signals during fracture healing. In this review, we first emphasize the importance of biochemical signals during fracture healing. Then, existing bioregulatory and coupled mechanobioregulatory models are presented. Finally, some limitations and possible solutions are discussed.

A novel modelling and simulation method of hip joint surface contact stress.

Understanding the hip joint surface contact stress distribution characteristics is helpful to determine hip joint biomechanical features and abnormal pathological behavior. Firstly, a 3-dimensional static hip joint biomechanical model is built using analytical method of model in order to study biomechanical properties including bearing area, stress distribution and the peak value of the contact stress of the femoral head, which reveals the relationship between the biomechanical properties and its geometric parameters. Secondly, based on the finite element analysis of the hip joint model, the contact stress distribution on the surface of femoral head is acquired under the condition of the different joint force and the acetabulum coverage rate. Finally, according to the evaluation of the femoral head surface stress and contact stress peak under different load distribution, accuracy and universality of the biomechanical model is verified.

BMP7 enhances the effect of BMSCs on extracellular matrix remodeling in a rabbit model of intervertebral disc degeneration.

Intervertebral discs (IVDs) provide stability and flexibility to the spinal column; however, IVDs, and in particular the nucleus pulposus (NP), undergo a degenerative process characterized by changes in the disc extracellular matrix (ECM), decreased cell viability, and reduced synthesis of proteoglycan and type II collagen. Here, we investigated the efficacy and feasibility of stem cell therapy using bone marrow mesenchymal stem cells (BMSCs) over-expressing bone morphogenetic protein 7 (BMP7) to promote ECM remodeling of degenerated IVDs. Lentivirus-mediated BMP7 over-expression induced differentiation of BMSCs into an NP phenotype, as indicated by expression of the NP markers collagen type II, aggrecan, SOX9 and keratins 8 and 19, increased the content of glycosaminoglycan, and up-regulated ß-1,3-glucuronosyl transferase 1, a regulator of chondroitin sulfate synthesis in NP cells. These effects were suppressed by Smad1 silencing, indicating that the effect of BMP7 on ECM remodeling was mediated by the Smad pathway. In vivo analysis in a rabbit model of disc degeneration showed that implantation of BMSCs over-expressing BMP7 promoted cell differentiation and proliferation in the NP, as well as their own survival, and these effects were mediated by the Smad pathway. The results of the present study indicate the beneficial effects of BMP7 on restoring ECM homeostasis in NP cells, and suggest potential strategies for improving cell therapy for the treatment of disc diseases.