Specimen-Specific Natural, Pathological, and Implanted Knee Mechanics Using Finite Element Modeling

There is an increasing incidence of knee pain and injury among the population, and increasing demand for higher knee function in total knee replacement designs. As a result, clinicians and implant manufacturers are interested in improving patient outcomes, and evaluation of knee mechanics is essential for better diagnosis and repair of knee pathologies. Common knee pathologies include osteoarthritis (degradation of the articulating surfaces), patellofemoral pain, and cruciate ligament injury and/or rupture. The complex behavior of knee motion presents unique challenges in the diagnosis of knee pathology and restoration of healthy knee function. Quantifying knee mechanics is essential for developing successful rehabilitation therapies and surgical treatments. Researchers have used in-vitro and in-vivo experiments to quantify joint kinematics and loading, but experiments can be costly and time-intensive, and contact and ligament mechanics can be difficult to measure directly. Computational modeling can complement experimental studies by providing cost-effective solutions for quantifying joint and soft tissue forces. Musculoskeletal models have been used to measure whole-body motion, and predict joint and muscle forces, but these models can lack detail and accuracy at the joint-level. Finite element modeling provides accurate solutions of the internal stress/strain behavior of bone and soft tissue using subject-specific geometry and complex contact and material representations. While previous FE modeling has been used to simulate injury and repair, models are commonly based on literature description or average knee behavior. The research presented in this dissertation focused on developing subject-specific representations of the TF and PF joints including calibration and validation to experimental data for healthy, pathological, and implanted knee conditions. A combination of in-vitro experiment and modeling was used to compare healthy and cruciate-deficient joint mechanics, and develop subject-specific computational representations. Insight from in-vitro testing supported in-vivo simulations of healthy and implanted subjects, in which PF mechanics were compared between two common patellar component designs and the impact of cruciate ligament variability on joint kinematics and loads was assessed. The suite of computational models developed in this dissertation can be used to investigate knee pathologies to better inform clinicians on the mechanisms surrounding injury, support the diagnosis of at-risk patients, explore rehabilitation and surgical techniques for repair, and support decision-making for new innovative implant designs

Effects of Scapular Notching and Bone Remodelling on Long-Term Fixation of the Glenoid Component in Reverse Shoulder Arthroplasty

Reverse shoulder arthroplasty (RSA) has been a proposed surgical treatment for severe rotator cuff deficiency associated with arthritis. Favourable clinical results for this type of prosthesis have been reported from short- and mid-term follow-up studies. However, the high revision rate (5% - 33%) at long-term follow up (i.e. greater than 6 years) is a concern. One of the principal factors leading to RSA failure is glenoid component loosening with an incidence of 5% - 38%. Therefore, one objective of this project is to investigate factors leading to long-term glenoid loosening. As various glenosphere positions have been proposed to minimize scapular notching, the other objective is to predict fixation strengths associated with these new surgical techniques. Scapular notching is one of the most frequently reported complications for Delta RSA, due to the high postoperative incidence of 50% to 96%. In this thesis, the study of scapular notching showed negative effects on the inferior screw safety and safety of the bone close to the screw. The study of initial stability showed that scapular notching may not destroy the good environment for bony ingrowth. Strain-induced bone remodelling has been an important factor for the bone loss after hip and knee joint prosthesis implantations. Effects of this factor on the bone loss after Delta RSA implantations were investigated. The results showed that bone resorption was considerable in the region close to the back of metagelene and the middle stem with a mean reduction of postoperative bone apparent density of approximately 63% at 8-year follow up. Thereby, postoperative bone loss could be caused by three factors: strain-induced bone resorption, scapular notching and osteolysis induced by the polyethylene wear particles. In this study, prosthesis fixations in the case of inferior positioning and downward tilting of the glenosphere were assessed using two parameters: strain-induced bone resorption and initial stability. It was found that inferior positioning may lead to early bone resorption due to the inferior shift of postoperative glenohumeral force. The downward tilting may cause significant increase of bone-prosthesis micromotions and may result in poor initial stabilities of glenoid prosthesis

Development of a Rigid Body Computational Model for Investigation of Wrist Biomechanics

The wrist is one of the most complex joints in the human body. As such, the wrist joint is difficult to model due to the number of bones involved and its intricate soft tissue interactions. Many studies have attempted modeling the wrist previously; however, the majority of these studies simplify the joint into two-dimensions or idealized mechanical joints to reduce the complexity of the simulation. While these approaches still yield valuable information, the omission of a third-dimension or geometry defined movements limits the models’ usefulness in predicting joint function under non-idealized conditions. Therefore, the goal of this study was to develop a computational model of the wrist joint complex using commercially available software, whereby joint motion and behavior is dictated by highly accurate three-dimensional articular contact, ligamentous constraints, muscle loads, and external perturbations only. As such, a computational model of the human wrist was created using computed tomography (CT) images of a cadaver right upper extremity. Commercially available medical imaging software and three-dimensional computer aided design (CAD) software were used to reconstruct the osteoarticular surfaces and accurately add soft tissue constraints, as well as calculate kinematic motion simulations. The model was able to reproduce physiologic motion including flexion/extension and radial/ulnar deviation. Validation of the model was achieved by comparing predicted results from the model to the results of a published cadaveric experiment that analyzed wrist function under effects of various surgical procedures. The model was used to replicate the exact testing conditions prescribed for the experiment, and the model was able to accurately reproduce the trends and, in many instances, the magnitudes of the range of motion measurements in the study. Furthermore, the model can now be used to predict the magnitudes for the joint contact forces within the wrist as well as the tension developed in ligaments in hopes locating potential areas of concern after these surgical procedures have been conducted, including further development of arthritis in the wrist and ligament breakdown

An In-Vitro and Finite Element Investigation on the Efficacy of Unloader Knee Braces on Meniscus Strain and Tibiofemoral Pressure

The medial and lateral menisci, situated in the knee joint, are most injured soft tissues in the human body. Meniscus injuries can be isolated or occur concurrently with an anterior cruciate ligament (ACL) injury. Certain tears are not amenable to surgical intervention and non-invasive treatment options such as unloader knee braces are theorized to benefit the knee joint during a medial meniscus injury. Unloader braces have shown favourable outcomes for medial osteoarthritis; however, there is a knowledge gap regarding the efficacy of these braces as an intervention for the meniscus. This study investigated the efficacy of two medial unloader braces (i.e., Rebound Cartilage and Unloader Fit) on the medial meniscus and tibiofemoral joint compartment during simulated activities of daily living (ADL) in healthy and injured ACL states. Posteromedial and anteromedial meniscus strains and tibiofemoral cartilage pressures were measured on cadaveric specimens (n=10) while replicating gait, double leg squats (DLS), and single leg squats (SLS) using a dynamic knee simulator. In a complementary study, the experimental boundary conditions were applied to a pre-existing 50th percentile male right leg finite element (FE) model and the three ADLs were simulated in both ACL states with a simulated 10 Nm valgus moment (VM) unloader brace effect. The computational approach investigated additional outcomes that could not be measured experimentally such as posterolateral meniscus strains. Descriptive statistics were calculated for experimental strain and pressure outcomes and an analysis of variance (ANOVA) was conducted. Descriptive statistics were calculated for FE strain and pressures, and a cross-correlation analysis (CORA) was performed to compare between the FE model and experiment. Both unloader braces resulted in significant reductions in mean and peak posteromedial meniscus strains during the ACL-intact state and significant differences in peak anteromedial meniscal strain (p.05). There were no significant differences in tibial cartilage pressures with the application of both braces during the ACL-intact state (p>.05). Both braces resulted in an intended valgus unload during DLS and gait, though not during SLS despite reductions in posteromedial meniscus strain during SLS. Strain and pressure outcomes revealed that the RC brace significantly outperformed the UF brace (p<.05), as intended by the manufacturer, moreover, this was more noticeable in the ACL-deficient state. The FE simulations demonstrated strong kinematic validity (CORA=0.74–0.99) with the experiments and the simulated ADLs matched experimental behaviours with ACL-deficient and VM conditions. FE posteromedial meniscus strain outcomes were within the experimental corridors and strain and pressure outcomes were within 1–2 SD of the mean experimental outcomes. Posterolateral meniscus strains were 7-16% higher than posteromedial meniscus strains and helped demonstrate affirmative unloading mechanics when compared to the unbraced scenario. The VM approximated unloader brace mechanics as evidenced by strain and pressure increases in the lateral meniscus and cartilage, respectively, and demonstrated higher efficacy in the ACL-intact state over the -deficient state, similar to the experiment. This study addressed a major literature gap in knee brace biomechanics by quantifying the efficacy of two commercially available unloader braces on the medial meniscus and demonstrated the viability of a FE approach to measure deep tissue strain. Future research can consider these braces for clinical research in patients with a healthy ACL and the FE model or framework can be used to investigate a variable brace moment BC, additional ADLs, or injury states such as meniscectomies/osteoarthritis

Musculoskeletal Modeling of The Human Elbow Joint

Title from PDF of title page viewed June 8, 2017Dissertation advisor: Antonis P. Stylianou and Majid Bani-YaghoubVitaIncludes bibliographical references (pages 130-139)Thesis (Ph.D.)--School of Computing and Engineering and Department of Mathematics and Statistics. University of Missouri--Kansas City, 2017Comprehensive knowledge of the in vivo loading of elbow structures is essential in understanding the biomechanical causes associated with elbow diseases and injuries, and to find appropriate treatment. Currently, in vivo measurements of ligament, and muscle forces, and cartilage contact pressures during elbow activities is not possible. Therefore, computational models needs to be employed for prediction. A dynamic computational model in which muscle, ligament and articular surface contact forces are predicted concurrently would be the ideal tool for patient specific pre-operative planning, computer aided surgery and rehabilitation. Computational models of the elbow have been developed to study joint behavior, but all of these models have limited applicability because the joint structure was modeled as an idealized joint (e.g. hinge joint) rather than a true anatomical joint. Three dimensional studies of elbow passive motion showed that the elbow does not function as a simple hinge joint. An accurate elbow model should reflect the intrinsic laxity of the elbow especially for clinical applications. Presented here are methods for developing an anatomically based computational model of the human elbow joint that replicates the mechanical behavior of the joint and is capable of concurrent prediction of articular contact, ligament, and muscle forces under dynamic conditions. The model performance was evaluated in both a cadaveric study and a living human subject experiment. The validated models were then used to investigate the effects of medial and lateral collateral ligament deficiency on elbow joint kinematics, ligament loads, and articular contact pressure distribution.Introduction -- Background -- Prediction of elbow joint contact mechanics in the multibody framework -- Lateral collateral ligament deficiency of the elbow joint: a modeling approach -- A modeling approach to simulating medial collateral ligament deficiency of the elbow joint -- Muscle driven elbow joint simulation: a computational approach -- Conclusio

Supervised Deep Learning with Finite Element Synthetic Data for Force Estimation in Robotic-assisted Surgery

The prevalence of robot-assisted minimally invasive surgery on the liver has increased exponentially. Having accurate, real-time knowledge of force during robotic-assisted surgical procedures is vital for safe surgery. Many techniques have been proposed in the literature to tackle this concern, from deploying force sensors to physics-based modeling of the robot and, more recently, learning-based force prediction. For a high-fidelity force measurement, sensors should be integrated at the instrument's tip, close to the surgical site, which brings sterilization, biocompatibility, and MRI compatibility concerns. On the other hand, Dynamic robot modeling may be precise in a specific setting, but it suffers from the lack of generalization encountering unseen settings. Considering the drawbacks and deficits of mentioned methods, indirect force estimation via deflection measurement through imaging techniques is investigated as an alternative solution, generally done via machine learning methods. Almost all previous studies are either supervised learning, where data are labeled with ex-vivo ground truth, or unsupervised or semi-supervised learning, where outcomes are promising but not adequate. This study investigated indirect force prediction for the human liver through a developed deep autoencoder model as a supervised deep learning method trained via synthetic data generated by finite element (FE) simulation. This method took advantage of various patient-specific livers parameters and geometries extracted from CT images. The Hyperelastic modeling of the soft tissue is considered and assessed with various hyperelastic models. The uncertainty due to the surgical tool's occlusion is addressed in this model, and a novel state vector was proposed to improve the accuracy and generalisability of the prediction. In addition, the impact of the bounded region on the model's accuracy was evaluated. It was shown that the proposed method could predict the external force on an unseen tissue with different geometry and mechanical properties. The accuracy of force prediction considering tool occlusion noise diminishes by 4.2 percent, which is in an acceptable range. The accuracy of presented model for various scenarios ranges from 95 to 88 percent. Model's results have been evaluated by predicting the force encountering the surface deformation of an unseen liver geometry and constitutive model where the mean absolute error of prediction is 0.249 Newton

Book of Abstracts 15th International Symposium on Computer Methods in Biomechanics and Biomedical Engineering and 3rd Conference on Imaging and Visualization

In this edition, the two events will run together as a single conference, highlighting the strong connection with the Taylor & Francis journals: Computer Methods in Biomechanics and Biomedical Engineering (John Middleton and Christopher Jacobs, Eds.) and Computer Methods in Biomechanics and Biomedical Engineering: Imaging and Visualization (JoãoManuel R.S. Tavares, Ed.). The conference has become a major international meeting on computational biomechanics, imaging andvisualization. In this edition, the main program includes 212 presentations. In addition, sixteen renowned researchers will give plenary keynotes, addressing current challenges in computational biomechanics and biomedical imaging. In Lisbon, for the first time, a session dedicated to award the winner of the Best Paper in CMBBE Journal will take place. We believe that CMBBE2018 will have a strong impact on the development of computational biomechanics and biomedical imaging and visualization, identifying emerging areas of research and promoting the collaboration and networking between participants. This impact is evidenced through the well-known research groups, commercial companies and scientific organizations, who continue to support and sponsor the CMBBE meeting series. In fact, the conference is enriched with five workshops on specific scientific topics and commercial software.info:eu-repo/semantics/draf

Biomechanical investigation of the factors related to pedicle screw fixation strength

Spinal pathologies or injuries can severely compromise the quality of life for the patients. The surgical intervention is often performed using internal fixation devices. Fixation with pedicle screws is a well-established method providing spinal stability and deformity correction. However, reported rates of fixation failure because of screw loosening have become a major concern, especially with the appearance of new and more powerful surgical techniques. Numerous experimental studies have been devoted to pedicle screw fixation strength evaluation. The evaluation methods are commonly including preoperative measurements of bone mineral density, screw insertional torque measurement and pullout tests. Bone mineral density measurement gives only to some extent an estimation of the pedicle screw fixation strength. Several studies indicated that the screw insertional torque measurement can provide predictive information on the fixation strength. However, the latter was not confirmed by other studies. This controversy illustrates the need for improving the understanding of factors related to pedicle screw fixation strength. In addition, there is a need for better understanding the mechanisms of pedicle screw loosening leading to failure and their effects on the fixation strength. The main objective of this doctoral thesis was to improve the understanding on the mechanisms of pedicle screw loosening and the factors related to pedicle screw fixation strength. This objective is related to two hypotheses: 1) the indentation force measured while performing the pilot hole and the torque observed during screw insertion are related to the screw pullout force and stiffness; 2) cyclic bending load (toggling) on pedicle screw in craniocaudal (CC) and mediolateral (ML) directions loosens the screw and affects the pullout force and stiffness. Three specific objectives were defined to verify the hypotheses using two experimental protocols. The first specific objective was to develop and validate tools measuring the indentation force while performing the pilot hole and the insertional torque during pedicle screw insertion. The second objective was to compare the screw loosening mechanisms through toggling in different modes and evaluate their effects on pedicle screw pullout force and stiffness. Finally, the third objective was to establish the relationships between the indentation force, the insertional torque and the screw pullout force and stiffness. The first protocol was performed on synthetic bone surrogates mainly to explore the first specific objective. Furthermore, to account for the effect of various bone densities and toggling modes on pullout force and stiffness, pedicle screw were pulled out with and without toggling from synthetic bone surrogates of three different densities. With five repetitions, a total of 36 trials have been completed. Finally, potential relationships between the indentation force and the insertional torque with the pullout force and stiffness were explored. The second protocol was performed on porcine vertebrae to investigate the second and the third specific objectives. As the second specific objective, three toggling modes (CC, ML and no toggling (NT)) were performed on porcine lumbar vertebrae ranging from L1 to L3. The screws were then submitted to axial pullout test. A complete design of experiment with two factors and three levels (32 = 9 trials) was used to investigate on the main effect of toggling mode and vertebral level on screw pullout force and stiffness, as well as their quadratic interactions. With five repetitions, a total of 54 trials were performed on 27 isolated vertebrae, using both pedicles. Finally, potential relationships were investigated between the indentation force while performing a pilot hole, the insertional torque during screw insertion, and the pullout force and stiffness with and without toggling. The results of the first protocol suggest that screw toggling significantly affects the pullout force (P = 0.01) and stiffness (P < 0.0001). A higher pullout force and stiffness was demonstrated for higher density without toggling. The effect of density was higher than the effect of toggling on pullout force. The indentation force while performing the pilot hole was significantly correlated to pullout force and stiffness (r = 0.99, P < 0.0001 and r = 0.92, P < 0.0001 respectively). Strong correlations were also shown between the insertional torque during screw insertion and the pedicle screw pullout force and stiffness (r = 0.98, P < 0.0001 and r = 0.91, P < 0.0001 respectively). The study on porcine vertebrae showed that screw toggling significantly affects the pullout force (P = 0.0004) and stiffness (P 0.85, P < 0.0001). For pullout force without toggling BMD and pedicle area were the main contributing factors to the regression model. For the stiffness with and without toggling, the indentation force was the single best factor with highest contribution to the regression model. In conclusion, pedicle screw toggling significantly affects the pedicle screw pullout force and stiffness. Screw toggling, in particular CC toggling, should be considered in the biomechanical evaluation of pedicle screw fixation strength. Furthermore, the contribution of toggling was more important on the stiffness than the pullout force. The effect of vertebral level should be considered in determining the fixation strength. The developed instruments and methods for indentation force measurement during pilot hole creation and insertional torque measurement during screw insertion were reproducible, and provide valuable data to estimate pedicle screw pullout force and stiffness. The relationship between the pilot hole indentation force and screw insertional torque, and the screw pullout force and stiffness are a affected by the toggling mode. Indentation force and insertional torque measurements, together with BMD measurement, are recommended for a better estimation of pedicle screw fixation strength after CC toggling

A finite element study of the human cranium : the impact of morphological variation on biting performance

This thesis investigated the relationship between craniofacial morphology and masticatory mechanics using finite element analysis (FEA). Chapter 1 is a literature review of the relevant background: bone mechanics, jaw-elevator muscle anatomy, imaging techniques, FEA and geometric morphometrics.The second, third and fourth chapters comprise experimental work aiming to provide a framework for FE model construction and loading. The second chapter aimed to validate the method for FE model building and assess the sensitivity of models to simplifications. Models with simplified bone anatomy and resolution predicted strains close to those measured experimentally. The third chapter assessed the predictability of muscle cross-sectional area (CSA) from bony features. It was found that muscle CSA, an estimator of muscle force, has low predictability. The fourth chapter assessed FE model sensitivity to variations in applied muscle forces. Results showed that a cranial FE model behaved reasonably robustly under variations in the muscle loading regimen.Chapter 5 uses the conclusions from the previous studies to build FE models of six human crania, including two individuals with artificial deformations of the neurocranium. Despite differences in form and the presence of deformation, all performed similarly during biting, varying mainly in the magnitudes of performance parameters. The main differences related to the form of the maxilla, irrespective of neurocranial deformation. The most orthognatic individuals with the narrowest maxilla showed the most distinctive deformation during incisor and molar bites, and achieved the greatest bite force efficiency. However, bite forces were similar among individuals irrespective of the presence of artificial deformation. This appears to relate to the preservation of normal dental occlusion, which in turn maintains similar loading and so morphogenesis of the mid face. Altogether, the results of this thesis show that FEA is reliable in comparing masticatory system functioning and point to how variations in morphology impact skeletal performance