Computational Models of Articular Cartilage

Unveiling the mechanical role of radial fibers in meniscal tissue: Toward structural biomimetics

Can the meniscus affect the nature of a chondrocyte?

Gait analysis using 3D motion capture systems provides joint kinematic and kinetic analysis results such as joint relative angles and moments that can be use used to evaluate the degrees of pathological gait patterns. However, the complex data produced using these 3D motion capture systems can only analyzed by experts, because the gait analysis is highly coupled to the kinematics of each joint. Therefore, several Several previous studies using gait analysis have relied on the data compression technique to represent gait deviation from the average normal profiles as a single value. Even though it is important to evaluate gait pathologies at the joint level, all these previous studies have just used a single value to evaluate the pathological gait pattern. Using just one variable for evaluation of a gait is limited in terms of determining which joint movement patterns are getting better during rehabilitation. Therefore, in this study, a method suitable for evaluating gait deviation during a gait was developed to provide three indices for the hip, knee and ankle joints. In addition, to validate the proposed method in clinical cases, experimental tests were conducted on thirty thirty-six normal walkers and six patients with cerebral palsy. Furthermore, to validate the proposed method in regards to rehabilitation, experimental tests were conducted on three classified walking groups with imposed ankle equinus constraints. The JNI for the hip joint, knee joint and ankle were 8.78 (±3.70), 2.92 (±3.25) and 8.79 (±4.38), respectively, in the normal walking group. However, these values were significantly different for the pathological walking group with cerebral palsy. The JNI of the hip joint, knee joint and ankle joint were 203.73 (±171.59), 81.23 (±52.13) and 248.39 (±149.99), respectively, for this group. There were also differences between any two of the three classified groups with imposed ankle equinus constraints. In particular, the JNI of the ankle joint was statistically different at the p<0.01 level, and this parameter clearly increased as the degree of the imposed ankle equinus was increased. These results demonstrate that the proposed JNI can be used as a scalar factor to evaluate the angular deviation of each joint in normal and patient groups. In addition, this approach can be adapted to evaluate rehabilitation and pre/post surgery.

To establish a 3D finite element model of normal knee joint involved its meniscus, which can be used to simulate the anatomical morphology and characteristics of human knee joint, to verify the validity of the model by preliminary FEA mechanical analysis, and explain partially biomechanical mechanisms of meniscus. CT and MRI data were harvested by scanning the knee joint of a healthy male volunteer, and then these data were imported into Mimics 10.01 software and Geomagic Studio software to constructed the 3D models of tissue structures of knee joint. These models were combined to constructed the 3D model of intact knee joint and meshed in ANSA software. Therefore the finite element model of intact knee joint was established. Finally, after the definitionof its material behavior, boundary conditions and loading. The finite element model of knee joint was analyzed and verified using ANSYS software. Meanwhile The biomechanical properties of meniscus were analyzed. The complete knee finite element model composed of bone, meniscus, articular cartilage, and major ligaments was established. It could effectively simulate the anatomical morphology and characteristics of knee joint and its meniscus. The contact area of medial meniscus was 771.05 mm2, while the contact area of lateral meniscus was 634.31 mm2, and the ratio was 1.216. The stress distribution was uniform, but the stress of the medial meniscus was higher than that of the lateral meniscus, and the peak stress located in the posterior horn of the medial meniscus and the anterior horn of the lateral meniscus, respectively, and the peak stress value was 4.11 MPa. The maximum displacement of the meniscus was located in body, and the displacement of the medial meniscus was more remarkable than that of the lateral meniscus, and the maximum displacement value is 0.33 mm. The obtained finite element analysis results corresponded to that reported in the literature, which mean the model's reliability. The established finite element model of knee joint are proved to be have validity, and is a useful model for finite element analysis of meniscus tear and menisectomy. The results of finite element analysis can explain partially biomechanical mechanisms of meniscus which can provide theoretical guidance for clinical treatment of meniscus injury.

Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): CVON eDETECT 2015-12 Background Patients with genetic cardiomyopathies mostly remain asymptomatic until the occurrence of life-threatening arrhythmias and sudden cardiac death. The responsible pro-arrhythmic mechanisms, as well as the indicators for pro-arrhythmia, often remain unclear. Current research approaches are commonly based on experimental animal models or clinical data obtained from mutation carriers. The translation (and bridging) of results obtained from experimental models to humans and scale integration of these findings remains challenging. As a consequence, clinical relevance is often disputed. In light of these challenges, computer modelling shows strong potential for its ability to capture the complex dynamics of the cardiovascular system across different scales. Purpose We therefore aim to develop a multiscale electromechanical computer model coupling electrophysiology, sarcomere dynamics (contractility), whole-heart function and hemodynamics to investigate mechanisms (resulting from genetic predisposition to cardiomyopathy) of arrhythmogenicity and cardiac dysfunction in these patients. Methods We coupled our previously published model of cellular electromechanics to the CircAdapt computer model of the heart and circulation. Electromechanical coupling was performed through the amount of calcium bound to troponin (as described in the cellular model). The same electrophysiological properties were assumed in all cardiac walls. Diffusion of calcium from the sarcolemmal space to the membrane was described phenomenologically through a resistance model. Results Simulated hemodynamics properties were in range with control values with LVEDV = 110.8mL, LVESV = 38.7mL, RVEDV = 99.2mL, mLAP = 10.2mmHg, mRAP = 4.0mmHg. At the cellular level, sarcolemmal calcium transients showed the effect of mechanical change as illustrated by the bump in CaT. This effect was attenuated at the membrane due to the effect of diffusion. Alterations in the functionality of molecular entities underlying calcium homeostasis recapitulated cellular experimental findings as expected illustrated by implementing changes in adrenergic signaling. Conclusions We have established a new multiscale electromechanical computer model describing electrophysiology, sarcomere mechanics and hemodynamics. The model simulates normal values in the control situation. Current work focusses on parameter sensitivity analysis and validation. Feeding this new model with experimentally obtained data from patient-specific models (ranging from individual cells to e.g. transgenic mouse models based on relevant mutations) therefore has potential to bridge the gap between pathogenic experimental models and patient data. This will add to the understanding of underlying mechanisms responsible for disease onset and progression, and furthermore could develop into a tool to identify patients/mutation carriers at risk for severe disease outcome. Abstract Figure.

The successful development of cartilage repair treatments for the knee requires understanding of the biomechanical environment within the joint. Computational finite element models play an important role in non-invasively understanding knee mechanics, but it is important to compare model findings to experimental data. The purpose of this study was to develop a methodology for generating subject-specific finite element models of porcine tibiofemoral joints that was robust and valid over multiple different constraint scenarios. Computational model predictions of two knees were compared to experimental studies on corresponding specimens loaded under several different constraint scenarios using a custom designed experimental rig, with variations made to the femoral flexion angle and level of tibial freedom. For both in vitro specimens, changing the femoral flexion angle had a marked effect on the contact distribution observed experimentally. With the tibia fixed, the majority of the contact region shifted to the medial plateau as flexion was increased. This did not occur when the tibia was free to displace and rotate in response to applied load. These trends in contact distribution across the medial and lateral plateaus were replicated in the computational models. In an additional model with the meniscus removed, contact pressures were elevated by a similar magnitude to the increase seen when the meniscus was removed experimentally. Overall, the models were able to capture specimen-specific trends in contact distribution under a variety of different loads, providing the potential to investigate subject-specific outcomes for knee interventions.

Repetitive magnetic stimulation induces synaptic plasticity through cooperative pre- and postsynaptic activation

Transcranial direct current stimulation (tDCS) is a neuromodulatory technique that delivers low-intensity currents facilitating or inhibiting spontaneous neuronal activity. Such noninvasive electrotherapies have a number of advantages that have been exploited in clinical practice; in particular, tDCS dose is easily customized by varying electrode number, position, size, shape, and current. Recent developments in computational models have further customized dose to individual subjects and cases. Finite Element Method models developed from high-resolution magnetic resonance imaging (MRI) scans are among the tools available today. Designing and interpreting these models while aware of their limitations can affect the rational design of electrotherapy as evidenced in studies combining computer modeling and clinical data. Though modeling for noninvasive brain stimulation is still in its development phase, it is predicted that with increased validation, dissemination, simplification, and democratization of modeling tools, computational forward models of neuromodulation will become useful tools to guide the optimization of clinical electrotherapy. As an example of tDCS customization and dose design, case studies of computational modeling in susceptible populations are discussed in the final section.

Recent advances in computational modeling have led to significant discoveries about the representation and acquisition of phonological knowledge and the limits on language learning and variation. These discoveries are the result of applying computational learning models to increasingly rich and complex natural language data while making increasingly realistic assumptions about the learning task. This article reviews the recent developments in computational modeling that have made connections between fully explicit theories of learning, naturally occurring corpus data, and the richness of psycholinguistic and typological data possible. These advances fall into two broad research areas: ( a) the development of models capable of learning the quantitative, noisy, and inconsistent patterns that are characteristic of naturalistic data and ( b) the development of models with the capacity to learn hidden phonological structure from unlabeled data. After reviewing these advances, the article summarizes some of the most significant consequent discoveries.

BackgroundPost-traumatic knee osteoarthritis affects an estimated one in two people within a decade of traumatic knee injury. While altered biomechanics in older adults are associated with the onset and progression of insidious-onset knee osteoarthritis, the relationship between biomechanics and post-traumatic osteoarthritis is less clear.ObjectiveWe aimed to evaluate associations between knee biomechanics and future structural and symptomatic outcomes post-surgery for traumatic knee injuries.MethodsWe systematically searched MEDLINE, EMBASE, Scopus, CINAHL, and SPORTDiscus from inception until May 2025. The eligibility criteria were studies that: (1) included participants post-surgery for traumatic knee injuries; (2) assessed knee biomechanics (kinetics, kinematics) during dynamic tasks (e.g. walking, hopping); and (3) reported longitudinal associations between early knee biomechanics and future post-traumatic osteoarthritis outcomes, including joint structure (imaging) or symptoms (patient-reported outcomes). Meta-analyses were completed where possible, with the remaining studies synthesised narratively due to heterogeneity precluding meta-analysis.ResultsWe included 18 studies (structure = 12, symptoms = 6); 17 following anterior cruciate ligament reconstruction and one post-meniscectomy. Meta-analysis of three studies examined the association between patellofemoral contact force up to 1-year post-anterior cruciate ligament reconstruction and future cartilage structure at 1–5 years, assessed via T2 relaxation times and progression of cartilage defects on magnetic resonance imaging. Lower patellofemoral contact force was associated with worse future trochlear cartilage structure (r = − 0.48, 95% confidence interval − 0.63, − 0.31; I2 = 0%), but the association with patellar cartilage was not significant (r = − 0.09, 95% confidence interval − 0.30, 0.12; I2 = 0%). A meta-analysis of three studies found no relationship between joint kinetics (e.g. knee flexion moment or knee adduction moment) and future structural outcomes in the tibiofemoral compartment, including T1 rho relaxation times, cartilage defects on magnetic resonance imaging and radiographic osteoarthritis. Narrative synthesis of other studies found that lower kinetic measures (e.g. knee flexion moment, knee adduction moment) were associated with worse future trochlear cartilage, but relationships with patellar cartilage and tibiofemoral joint structure were inconsistent. For symptoms, although time post-surgery appears to influence associations with mechanical loading, lower measures of frontal plane kinetics (e.g. knee adduction moment, medial ground reaction force) were associated with better future symptoms regardless of the timepoint.ConclusionsUnderloading of the patellofemoral joint within the first year post-anterior cruciate ligament reconstruction is associated with worse patellofemoral cartilage, a pattern not observed in the tibiofemoral joint. Clinicians should consider optimising loading interventions and addressing modifiable biomechanical alterations post-surgery to preserve cartilage health and reduce symptoms.Protocol RegistrationPROSPERO: CRD42024504099.Supplementary InformationThe online version contains supplementary material available at 10.1007/s40279-025-02288-1.

PurposeOsteoarthritis (OA) is one of the most common pathological conditions to affect the human knee joint. In order to analyse the biomechanical causes and effects of OA, accessing the internal structures such as cartilage or the menisci directly is not possible. Therefore, computational models can be used to study the effects of OA on the stresses and strains in the joint and the susceptibility to deformations within the knee joint.MethodsIn this study, a three-dimensional finite element model of a knee complex was constructed using MRI scans. Medical image processing software was used to create accurate geometries of bones, articular cartilages, menisci, patella, patella tendon and all the relevant ligaments. Finally, a 3D model of OA knee joint was created with a few changes to the cartilage. The cartilage was thinned, and the material properties were altered in order to simulate OA in the joint. 3D gait measurements were analysed to define loading and boundary conditions.ResultsThe developed model analysed the possibility of osteoarthritis. It was shown that the medial regions of cartilage layers and menisci in the knee joint sustain higher values of stress for OA conditions, while for the healthy knee, the stresses are more evenly distributed across the cartilage in the medial and lateral regions.ConclusionThe results suggest that any treatment for knee osteoarthritis should focus more on the medial region of the tibiofemoral cartilage in order not to cause degradation.

This is the second part of the paper related to the exploration of deformation machining technology (DMT), originally developed at Bauman Moscow State Technical University, as it may apply to making electrical joints and comparing their performance to bolted and welded electrical joints. The DMT process is used to generate tooth-like profiles on two opposing surfaces that make the electrical joints which are later joined by applying a mechanical load. Part I contained a more detailed explanation of the DMT process and the description of the results of computer modeling of DMT joints in copper and aluminum. This paper provides the experimental results of the mechanical and electrical performance of copper and aluminum DMT joints which were compared to bolted and welded electrical joints of identical geometries. Measurements of tensile strength and electrical resistance, after thermal cycling and short-circuit testing, show equivalent or better performance of copper DMT joints compared with copper bolted and welded joints. In addition, it is observed that copper DMT joints have superior performance when compared with aluminum DMT joints, this was attributed to lesser gap filling and the springback effect that occurs after the mechanical load for making the joint is removed. The computer modeling results reported in Part I of this paper support these observations.

In this research, we designed a universal graph model. We targeted this work on improving graph data organization representation, flexible formation of graph substructures for complex system modeling and generic processing of data organization. We form coherently composed graph modeling features including inheritance hierarchy of basic graph types, data participating graphs of multiple aspects, hierarchically composed and connected graphs, and property-based graph models based on existing graph models. Design cases are used to illustrate its achievement of our design goal. Keywords—graph theory; graph model, multi-aspect graph; hierarchical graph I. INTRODUCTION Computer modeling plays a key role to apply computer's capability in various fields of applications. Effective support of computer modeling should consist of data representation capability, data access and navigation capability, and generic operations for forming more general and reusable generic algorithms. As computer applications keep growing complex in wider areas, we need enhanced computer models capable of supporting these applications. Graph data models are one of the most extensively used discrete mathematical models in computer modeling of various applications from VLSI circuit design, computer system design and modeling, network modeling, etc. Traditional graph libraries such as LEDA(1), Boost Graph Library(2), LINK(3), and GraphStream(4) focuses on single- level directed and undirected graph modeling. Lee's work(5) utilized decorator and visitor patterns to add new vertex data and attach processing during graph traversal. Pizzonia's (6) employed static object-oriented extension of graph property classes associated with corresponding graph operations. Bertault(7) employed an extensible graph property class hierarchy and dynamic property checking. Directed and undirected hypergraphs are not supported in these approaches. Hyperedges in hypergraphs can be represented as vertices in ordinary graphs. Hypergraphs cannot be treated as super types of directed and undirected graphs to support generic algorithms with ordinary graphs. On data organization point of view, these approaches provide various graph organization types but only as single- level specialized graph type. Each of them should be utilized distinctly. Once these graph models need to be combined in a complex data model, designers should add artificial data structures to join them together. Still, such combined data model or its selected subparts cannot be viewed and utilized as if in a single graph model. This requires designers to add more application-specific gluing data structures, processing codes of distinct graph substructures and their gluing logic, and semantically similar but redundant non-generic codes. It thus hinders effective development and reuse of computer models for various complex applications. From our literature survey, we did not find any previous work providing combinational features for flexibly composing graph structures. Our design goal lies in three improvement directions, representation of complex system data organization, flexible formation of graph substructures for processing, and generic processing of data organization as well as individual data. Our main approach is to form coherently composed graph modeling features including inheritance hierarchy of basic graph types, vertex data participating in graphs of multiple aspects, hierarchically composed and connected graphs, and property-based graph models based on existing graph models. It forms a universal graph model of combinations of complex graph-oriented data organizations, flexibly forms various virtual graph substructures for complex system modeling and processing, and support generic processing capability at the graph structure levels and at the leaf data levels. In section 2, we describe refined design goals and the approach of our work. In the following sections, we in sequence introduce planned composed graph modeling features of our universal graph model, including generic accesses among basic graph models, joining multiple graphs into a multi-aspect graph model, generic structuring of graph models, and generic accesses of property-based graph models. In section 7, we introduce its software design and a design case. The last section concludes this research.

Comparative assessment of knee joint models used in multi-body kinematics optimisation for soft tissue artefact compensation.

The kinematics of human knee joint mainly includes the all degree of freedom motion of human knee joint. The human knee joint is the most complex structure of human anatomy and thus it also has high risk of failure. This joint may fail due to failure in ligaments, bone or any other component of the knee joint. Thus, the motion can be restored through the application of prosthetic knee joint. By comparing various single axis and polycentric prosthetic knee designs on the basis of maximum stress induced, manoeuvrability, weight and an optimal model could be developed that will not only have lightweight but will also include easy and low-cost manufacturing. Simulation-based finite element analysis was done on a single axis and two polycentric knee prosthetic knee designs using ANSYS WORKBENCH 18.1.