Development Of A Finite Element Pelvis And Lower Extremity Model With Growth Plates For Pediatric Pedestrian Protection

Finite element (FE) model is a useful tool frequently used for investigating the injury mechanisms and designing protection countermeasures. At present, no 10 years old (YO) pedestrian FE model has been developed from appropriate anthropometries and validated against limitedly available impact response data. A 10 YO child FE pelvis and lower extremities (PLEX) model was established to fill the gap of lacking such models in this age group. The baseline model was validated against available pediatric postmortem human subjects (PMHS) test data and additional scaled adult data, then the PLEX model was integrated to build a whole-body FE model representing a 10 YO pedestrian. Additional investigations revealed that the immature tissues, growth plates (GPs), should be explicitly modeled because they have different mechanical properties than the surrounding bones. Epidemiological data revealed that GP accounted for a large portion of pediatric fractures. To investigate the GP’s material property for further advancement of the baseline PLEX FE model for simulating impact mechanical responses, a series of tensile and shearing experiments on porcine bone-GP-bone units were carried out. The GPs from the femoral head, distal femur, and proximal tibia of 20-weeks-old piglets were tested, under different strain rates. Randomized block ANOVA was conducted to determine the effects of anatomic region and strain rate on the material properties of GPs. By comparing the porcine experimental data to the limited data obtained from tests on human subjects reported in the literature, an optimal conversion factor was derived to correlate the material properties of 20-week-old piglet GPs and 10 YO child GPs. A transversely isotropic hyperelastic material model (MAT_92 available in LS-DYNA) with added viscosity was adopted to mimic the GP tissues. After a series of optimization procedures, the material parameter sets needed for MAT_92 were determined to represent the GPs of a 10 YO child. To further explore the GP modeling techniques, a sub-model representing the proximal femur was extracted from the PLEX model. The femoral head GP in the sub-model was modeled using the geometry from CT scans and the material properties from early optimizations. FE simulations of femoral head shearing were conducted on the sub-model to determine other GP modeling settings. In the following technical application, similar GP modeling techniques were implemented to model the GPs at the hip and knee regions to update the baseline PLEX model, and further the whole-body model. An SUV-to-pedestrian impact scenario was simulated using the updated whole-body model, the remarkable influences of the GPs on the stress distributions in the PLEX were quantitatively assessed

Advancements in Prosthetics and Joint Mechanisms

abstract: Robotic joints can be either powered or passive. This work will discuss the creation of a passive and a powered joint system as well as the combination system being both powered and passive along with its benefits. A novel approach of analysis and control of the combination system is presented. A passive and a powered ankle joint system is developed and fit to the field of prosthetics, specifically ankle joint replacement for able bodied gait. The general 1 DOF robotic joint designs are examined and the results from testing are discussed. Achievements in this area include the able bodied gait like behavior of passive systems for slow walking speeds. For higher walking speeds the powered ankle system is capable of adding the necessary energy to propel the user forward and remain similar to able bodied gait, effectively replacing the calf muscle. While running has not fully been achieved through past powered ankle devices the full power necessary is reached in this work for running and sprinting while achieving 4x’s power amplification through the powered ankle mechanism. A theoretical approach to robotic joints is then analyzed in order to combine the advantages of both passive and powered systems. Energy methods are shown to provide a correct behavioral analysis of any robotic joint system. Manipulation of the energy curves and mechanism coupler curves allows real time joint behavioral adjustment. Such a powered joint can be adjusted to passively achieve desired behavior for different speeds and environmental needs. The effects on joint moment and stiffness from adjusting one type of mechanism is presented.Dissertation/ThesisDoctoral Dissertation Mechanical Engineering 201

Can a comprehensive transition plan to barefoot running be the solution to the injury epidemic in American endurance runners?

Fossils belonging to the genus Homo, dating as far back as two million years ago, exhibit uniquely efficient features suggesting that early humans had evolved to become exceptional endurance runners. Although they did not have the cushion or stability-control features provided in our modern day running shoes, our early human ancestors experienced far less of the running-related injuries we experience today. The injury rate has been estimated as high as 90% annually for Americans training for a marathon and as high as 79% annually for all American endurance runners. There is an injury epidemic in conventionally shod populations that does not exist in the habitually unshod or minimally shod populations around the world. This has led many to conclude that the recent advent of highly technological shoes might be the problem. Although current literature has been inconclusive, there are two main limitations in virtually all of the studies: 1) transition phases of less than three months and 2) transition phases without rehabilitation exercises. These two aspects are key to the treatment of the structural consequences on the muscles and tendons of the foot and calf that habitually shod individuals have faced. This study includes a discussion of the cumulative consequences that lifelong shoe usage has on the development of the feet and lower legs. I propose a 78-week study that addresses the limitations of past studies by implementing a gradual, 32-week, multi-shoe transition complemented by an evidence-based rehabilitation program. I believe that this approach will restore strength and elasticity to muscles and tendons that have been inhibited by lifelong usage of overconstructed shoes and adequately prepare runners for the increased demand brought on by a­­­­­ changing running mechanic. This comprehensive, multifaceted transition plan to a fully minimalist shoe will provide novel insight into the ongoing barefoot debate. Can this approach finally demonstrate the proposed benefits of losing the shoes

The Design and Realization of a Sensitive Walking Platform

Caminante is a bipedal platform design to test sensitive walking. The robot was designed with all the characteristics that were deemed necessary in order to test successfully develop and test new control and wait generation systems that can be applied to all legged robots. A twelve degrees of freedom platform with series elastic actuators that mimics the major human leg joints was developed and constructed. The system uses cable driven SEA’s for compliance and force control. Two 36 tactile sensor arrays capable of measure shear and normal forces on the sole of the feet were developed to measure the forces generated by walking and develop better control schemes for the bipedal system

The mechanical response of a passive-dynamic ankle-foot- orthosis and its interaction with the lower limb during gait

The prescription of a passive dynamic ankle foot orthosis (PD-AFO), trademarked the Momentum, has improved functional outcome for many patients, though not all. The design features of the PD- AFO that account for this improvement, and the changes the PD-AFO introduces into gait, are not fully understood. This thesis aims to establish how the PD-AFO alters the external and internal loading of the foot during gait. Gait analysis was used to evaluate changes in external loading of the foot when wearing the PD-AFO (possible offloading). It was demonstrated that the PD-AFO reduced loading in the foot when walking, with maximum offloading seen during early stance. A novel methodology, using strain gauges, demonstrated the struts’ energy storage and return (ESAR) characteristics and ability to provide propulsive power during late stance. Finite element (FE) modelling was used to evaluate internal loading of the foot. A comprehensive development process was undertaken to build FE models of the foot and PD-AFO. By running multiple simulations of the FE model of the PD-AFO, design components whose mechanical characteristics may significantly alter gait were highlighted, such as the alignment of the posterior struts. The FE models of the foot and PD-AFO were combined to model the loading at a point during early stance; comparable results with data recorded experimentally was achieved. Simulation results demonstrated greater relative reduction in contact stresses, compared to contact force, at the subtalar joint. This suggested that PD-AFO’s influence on the subtalar joint angle may be an important design feature in the PD-AFO’s success. This research may help to predict who may be successfully aided by the PD-AFO, target research on design components that influence the mechanical response of the PD-AFO; and indicate potential long-term adverse effects of using the device as a result of changes to gait.Open Acces

Cancellous bone and theropod dinosaur locomotion. Part I—an examination of cancellous bone architecture in the hindlimb bones of theropods

This paper is the first of a three-part series that investigates the architecture of cancellous (‘spongy’) bone in the main hindlimb bones of theropod dinosaurs, and uses cancellous bone architectural patterns to infer locomotor biomechanics in extinct non-avian species. Cancellous bone is widely known to be highly sensitive to its mechanical environment, and has previously been used to infer locomotor biomechanics in extinct tetrapod vertebrates, especially primates. Despite great promise, cancellous bone architecture has remained little utilized for investigating locomotion in many other extinct vertebrate groups, such as dinosaurs. Documentation and quantification of architectural patterns across a whole bone, and across multiple bones, can provide much information on cancellous bone architectural patterns and variation across species. Additionally, this also lends itself to analysis of the musculoskeletal biomechanical factors involved in a direct, mechanistic fashion. On this premise, computed tomographic and image analysis techniques were used to describe and analyse the three-dimensional architecture of cancellous bone in the main hindlimb bones of theropod dinosaurs for the first time. A comprehensive survey across many extant and extinct species is produced, identifying several patterns of similarity and contrast between groups. For instance, more stemward non-avian theropods (e.g. ceratosaurs and tyrannosaurids) exhibit cancellous bone architectures more comparable to that present in humans, whereas species more closely related to birds (e.g. paravians) exhibit architectural patterns bearing greater similarity to those of extant birds. Many of the observed patterns may be linked to particular aspects of locomotor biomechanics, such as the degree of hip or knee flexion during stance and gait. A further important observation is the abundance of markedly oblique trabeculae in the diaphyses of the femur and tibia of birds, which in large species produces spiralling patterns along the endosteal surface. Not only do these observations provide new insight into theropod anatomy and behaviour, they also provide the foundation for mechanistic testing of locomotor hypotheses via musculoskeletal biomechanical modelling

A Generalized Method for Predictive Simulation-Based Lower Limb Prosthesis Design

Lower limb prostheses are designed to replace the functions and form of the missing biological anatomy. These functions are hypothesized to improve user outcome measures which are negatively affected by receiving an amputation – such as metabolic cost of transport, preferred walking speed, and perceived discomfort during walking. However, the effect of these design functions on the targeted outcome measures is highly variable, suggesting that these relationships are not fully understood. Biomechanics simulation and modeling tools are increasingly capable of analyzing the effects of a design on the resulting user gait. In this work, prothesis-aided gait is optimized in simulation to reduce both muscle effort and peak loads on the residual limb using a generalized prosthesis model. Compared to a traditional revolute powered ankle joint model, a two degree-of freedom generalized model reduced muscle activations by 50% and peak loads by 15%. Simulated prosthesis behaviors corresponding to the optimal gait patterns were translated into a two degree-of-freedom ankle-foot prosthesis design with powered bidirectional linear translation and plantarflexion. The prototype is capable of delivering up to 171 N-m of plantarflexion torque and 499 N of translation force, with 15° dorsi-/35° plantarflexion and 10 cm translation range of motion. The mass and height of the ankle-foot are 2.29 kg and 19.5 cm, respectively. The mass of the entire system including the wearable offboard system is 8.58 kg. This platform is designed to emulate the behavior of the simulated prosthesis, as well as be configurable to emulate alternate behaviors obtained from simulations with different optimization objectives. The prototype is controlled to replicate simulated walking patterns using a high level finite state controller, mid-level stiffness controller, and low level load controller. Closed loop load control has bandwidth of 15 Hz in translation and 7.2 Hz in flexion. Load tracking during walking with a single able-bodied human subject ranges from 93 to 159 N in translation and 4.6 to 21.3 N-m in flexion. The contribution of this work is to provide a framework for predictive simulation-based prosthesis design, evidence of its practical implementation, and the experimental tools to validate future predictive simulation studies