138 results found
Caillet AHD, Phillips ATM, Farina D, et al., 2021, Mathematical Relationships between Spinal Motoneuron Properties, BiorXiv
<jats:p>Our understanding of the behaviour of alpha-motoneurons (MNs) in mammals partly relies on our knowledge of the relationships between MN membrane properties, such as MN size, resistance, rheobase, capacitance, time constant, axonal conduction velocity and afterhyperpolarization period. Based on scattered but converging evidence, current experimental studies and review papers qualitatively assumed that some of these MN properties are related. In this systematic meta-analysis, we reprocessed the data from 40 experimental studies in adult cat, rat and mouse MN preparations in vivo to empirically derive mathematical relations between experimentally measured MN electrophysiological and anatomical properties. These mathematical relationships provide the first validated framework of MN-specific morphometric and electrophysiological properties that reproduce published experimental mammal data in vivo. These relationships moreover support the classic description of a MN as a membrane equivalent electrical circuit and describe for the first time the association between MN size and MN membrane capacitance and time constant. The obtained relationships finally indicate that motor units are recruited in order of increasing MN size, muscle unit size, MN rheobase, unit force recruitment thresholds and tetanic forces, but underlines that MN size and recruitment order may not be related to motor unit type.</jats:p>
Favier C, McGregor A, Phillips A, 2021, Maintaining bone health in the lumbar spine: routine activities alone are not enough, Frontiers in Bioengineering and Biotechnology, Vol: 9, ISSN: 2296-4185
Public health organisations typically recommend a minimum amount of moderate intensity activities such as walking or cycling for two and a half hours a week, combined with some more demanding physical activity on at least 2 days a week to maintain a healthy musculoskeletal condition. For populations at risk of bone loss in the lumbar spine, these guidelines are particularly relevant. However, an understanding of how these different activities are influential in maintaining vertebral bone health is lacking. A predictive structural finite element modelling approach using a strain-driven algorithm was developed to study mechanical stimulus and bone adaptation in the lumbar spine under various physiological loading conditions. These loading conditions were obtained with a previously developed full-body musculoskeletal model for a range of daily living activities representative of a healthy lifestyle. Activities of interest for the simulations include moderate intensity activities involving limited spine movements in all directions such as, walking, stair ascent and descent, sitting down and standing up, and more demanding activities with large spine movements during reaching and lifting tasks. For a combination of moderate and more demanding activities, the finite element model predicted a trabecular and cortical bone architecture representative of a healthy vertebra. When more demanding activities were removed from the simulations, areas at risk of bone degradation were observed at all lumbar levels in the anterior part of the vertebral body, the transverse processes and the spinous process. Moderate intensity activities alone were found to be insufficient in providing a mechanical stimulus to prevent bone degradation. More demanding physical activities are essential to maintain bone health in the lumbar spine.
Favier C, Finnegan M, Quest R, et al., 2021, An open-source musculoskeletal model of the lumbar spine and lower limbs: a validation for movements of the lumbar spine, Computer Methods in Biomechanics and Biomedical Engineering, Vol: 24, Pages: 1310-1325, ISSN: 1025-5842
Musculoskeletal models of the lumbar spine have been developed with varying level of detail for a wide range of clinical applications. Providing consistency is ensured throughout the modelling approach, these models can be combined with other computational models and be used in predictive modelling studies to investigate bone health deterioration and the associated fracture risk. To provide precise physiological loading conditions for such predictive modelling studies, a new full-body musculoskeletal model including a detailed and consistent representation of the lower limbs and the lumbar spine was developed. The model was assessed against in-vivo measurements from the literature for a range of spine movements representative of daily living activities. Comparison between model estimations and electromyography recordings was also made for a range of lifting tasks. This new musculoskeletal model will provide a comprehensive physiological mechanical environment for future predictive finite element modelling studies on bone structural adaptation. It will be made freely available on https://simtk.org/projects/llsm/.
Deane JA, Papi E, Phillips A, et al., 2020, Reliability and minimal detectable change of the ‘Imperial Spine’ marker set for the evaluation of spinal and lower limb kinematics in adults, BMC Research Notes, Vol: 13, ISSN: 1756-0500
ObjectivesAs a step towards the comprehensive evaluation of movement in patients with low back pain, the aim of this study is to design a marker set (three rigid segment spine, pelvic and lower limb model) and evaluate the reliability and minimal detectable change (MDC) of this marker set in healthy adults during gait and sit to stand (STS) tasks using three dimensional motion capture.ResultsThe ‘Imperial Spine’ marker set was used to assess relative peak angles during gait and STS tasks using the minimum recommended sample size (n = 10) for reliability studies with minimum Intraclass Correlation Coefficient (ICC) of 0.70, optimum ICC 0.90 and 9 trials replicated per subject per task. Intra- and inter-tester reliability between an experienced and inexperienced user was examined. ICC, mean, standard error (SEM), Bland Altman 95% limits of agreement (LOA) and MDC were computed.ICC values demonstrated excellent intra- and inter-tester reliability in both tasks, particularly in the sagittal plane (majority ICCs > 0.80). SEM measurements were lower in gait (0.8–5.5°) than STS tasks (1°-12.6°) as were MDC values. LOA demonstrated good agreement. The ‘Imperial Spine’ marker set is reliable for use in healthy adults during functional tasks. Future evaluation in patients is required.
Villette C, Zhang J, Phillips A, 2020, Influence of femoral external shape on internal architecture and fracture risk, Biomechanics and Modeling in Mechanobiology, Vol: 19, Pages: 1251-1261, ISSN: 1617-7940
The internal architecture of the femur and its fracture behaviour vary greatly between subjects. Femoral architecture and subsequent fracture risk are strongly influenced by load distribution during physical activities of daily living. The objective of this work is to evaluate the impact of outer cortical surface shape as a key affector of load distribution driving femoral structure and fracture behaviour. Different femur cortical shapes are generated using a statistical shape model. Their mesoscale internal architecture is predicted for the same activity regime using a structural optimisation approach previously reported by the authors and fracture under longitudinal compression is simulated. The resulting total volume of bone is similar in all geometries although substantial differences are observed in distribution between trabecular and cortical tissue. Greater neck-shaft and anteversion angles show a protective effect in longitudinal compression while a thinner shaft increases fracture risk.
Wadee MA, Phillips ATM, Bekele A, 2020, Effects of disruptive inclusions in sandwich core lattices to enhance energy absorbency and structural isolation performance, Frontiers in Materials, Vol: 7, ISSN: 2296-8016
The energy absorption and structural isolation performance of axially-compressed sandwich structures constructed with stiff face plates separated with an auxetic lattice core metamaterial is studied. Advances in additive manufacturing increasingly allow bespoke, carefully designed, structures to be included within the core lattice to enhance mechanical performance. Currently, the internal structure of the lattice core is deliberately disrupted geometrically to engineer suitable post-buckling behaviour under quasi-static loading. The desirable properties of a high fundamental stiffness and a practically zero underlying stiffness in the post-buckling range ensure that energy may be absorbed within a limited displacement and that any transfer of strain to an attached structure is minimized as far as is feasible. It is demonstrated that such disruptions can be arranged to enhance the panel performance. The concept may be extended to promote cellular buckling where the internal lattice buckles with densification occurring at defined locations and in sequence to absorb energy while maintaining a low underlying mechanical stiffness.
Favier C, Deane J, McGregor A, et al., 2019, Design and preliminary testing of a low-cost balance perturbation system for the evaluation of real life postural adjustment on public transport, Journal of Medical Engineering and Technology, Vol: 43, Pages: 356-362, ISSN: 0309-1902
Balance recovery mechanisms are of paramount importance in situations like public transport where sudden loss of equilibrium can occur. These mechanisms can be altered by aging or pathological disorders. However it is almost impossible to investigate these phenomena in real-life conditions, and the safe environment of a laboratory is needed. This paper investigates how jerk perturbations in the transverse plane similar to those experienced on public transport can be simulated in a controlled manner. A platform capable of producing horizontal perturbations with a person standing on it was developed. Accuracy, repeatability, and load sensitivity of the system were assessed with repeated trials in all four directions of movement. Comparison between the destabilising effect experienced on public transport and the postural response to perturbations from the platform was also made by tracking acceleration of the centre of mass of four subjects in these two situations. Results show that balance perturbations representative of real-life situations, such as standing on public transport, can accurately and repeatedly be produced in a safe and controlled environment with a low-cost and low-maintenance system. Coupled to motion capture technology, the system can be used for pathology assessment and rehabilitation treatments.
Zaharie D, Phillips A, 2019, A comparative study of continuum and structural modelling approaches to simulate bone adaptation in the pelvic construct, Applied Sciences, Vol: 9, Pages: 1-18, ISSN: 2076-3417
This study presents the development of a number of finite element (FE) models of the pelvis using different continuum and structural modelling approaches. Four FE models were developed using different modelling approaches: continuum isotropic, continuum orthotropic, hybrid isotropic and hybrid orthotropic. The models were subjected to an iterative adaptation process based on the Mechanostat principle. Each model was adapted to a number of common daily living activities (walking, stair ascent, stair descent, sit-to-stand and stand-to-sit) by applying onto it joint and muscle loads derived using a musculoskeletal modelling framework. The resulting models, along with a structural model previously developed by the authors, were compared visually in terms of bone architecture, and their response to a single load case was compared to a continuum FE model derived from computed tomography (CT) imaging data. The main findings of this study were that the continuum orthotropic model was the closest to the CT derived model in terms of load response albeit having less total bone volume, suggesting that the role of material directionality in influencing the maximum orthotropic Young’s modulus should be included in continuum bone adaptation models. In addition, the hybrid models, where trabecular and cortical bone were distinguished, had similar outcomes, suggesting that the approach to modelling trabecular bone is less influential when the cortex is modelled separately.
Phillips A, 2019, Structural modelling of trabecular bone adaptation using a Voronoi network, International Society of Biomechanics
Favier C, McGregor A, Phillips A, 2019, Subject specific multiscale modelling for the study of lumbar pathologies, 17th International symposium on computer simulation in biomechanics, Publisher: International Society of Biomechanics
Phillips A, 2019, Structural modelling of trabecular bone adaptation using a Voronoi network, ISB TGCS Symposium on Computational Simulation in Biomechanics, Publisher: International Society of Biomechanics
Phillips A, 2019, Modelling Trabecular Bone as a Voronoi Structure, Bone Research Society / British Orthopaedic Research Society combined meeting 2019
Structural finite element models of trabecular boneadaptation within the femur(1) and pelvis(2) usedrandomized networks of truss elements with straindue to axial force used as a driver for adaptation oftrabeculae cross-sectional areas. At the macro-scalethe adapted models successfully highlightedtrabecular trajectories and were used to predictfracture initiation and progression, in the femoralneck(3). The use of a truss network requires a highnodal connectivity (NC) defined as the number ofstructural elements representing trabeculaeconnecting to each node, in order to maintainstructural and computational stability. A minimumNC of 6 results from the orthotropic nature of theprincipal stress directions that bone is believed toform trajectories along, while higher NCs are requiredto resist multiple load cases that introduce sheardue to off axis loading compared to the principalstress directions obtained when adaptation is carriedout for a single load case.Recent micro-CT studies characterising the structuralarchitecture of trabecular bone(4) contradict thetrajectory hypothesis indicating frequent NC valuesof 3 and 4 with nodes having common structuralarrangements or motifs. A Voronoi network is astructural form that provides an abundance of nodeswith a NC of 4. The Voronoi method of partitioningspace around control points is implemented inRhino using the Grasshopper parametric designtool to create a network as a collection of node andelement definitions. The Abaqus finite elementsolver is used to analyse this network using beamelements with strains developed due to axial force,biaxial bending and torsion moments. An extendedbone adaptation approach is used to adapt thecross-sectional properties at multiple points alongthe length of each trabeculae.Initial results suggest using a Voronoi network is apromising approach to model trabecular boneadaptation and fatigue micro-fracture. Ongoingwork will investigate the iterative placement of thecontrol points used to construct
Favier C, McGregor A, Phillips A, 2019, Full body subject specific musculoskeletal model for complex spine movements, XXVII Congress of the International Society of Biomechanics
Kaufmann J, Phillips A, McGregor A, 2019, Investigating bone health in lower-limb amputees, 2019 Blast Injury Conference
Kaufmann J, Phillips A, McGregor A, 2019, Investigating bone health in lower-limb amputees, TGCS 2019 - 17th International Symposium on Computer Simulation in Biomechanics
Kaufmann J, Phillips A, McGregor A, 2019, Investigating bone health in lower-limb amputees, ISB/ASB 2019
Sperry MM, Phillips ATM, McGregor AH, 2019, Lower back pain and healthy subjects exhibit distinct lower limb perturbation response strategies: a preliminary study, Journal of Back and Musculoskeletal Rehabilitation, Vol: 32, Pages: 27-35, ISSN: 1053-8127
BACKGROUND: It is hypothesized that inherent differences in movement strategies exist between control subjects and those with a history of lower back pain (LBP). Previous motion analysis studies focus primarily on tracking spinal movements, neglecting the connection between the lower limbs and spinal function. Lack of knowledge surrounding the functional implications of LBP may explain the diversity in success from general treatments currently offered to LBP patients. OBJECTIVE: This pilot study evaluated the response of healthy controls and individuals with a history of LBP (hLBP) to a postural disturbance. METHODS: Volunteers (n= 26) were asked to maintain standing balance in response to repeated balance disturbances delivered via a perturbation platform while both kinematic and electromyographic data were recorded from the trunk, pelvis, and lower limb. RESULTS: The healthy cohort utilized an upper body-focused strategy for balance control, with substantial activation of the external oblique muscles. The hLBP cohort implemented a lower limb-focused strategy, relying on activation of the semitendinosus and soleus muscles. No significant differences in joint range of motion were identified. CONCLUSIONS: These findings suggest that particular reactive movement patterns may indicate muscular deficits in subjects with hLBP. Identification of these deficits may aid in developing specific rehabilitation programs to prevent future LBP recurrence.
Wadee MA, Phillips ATM, Bekele A, 2019, From buckliphobes to buckliphiles: Recent developments in exploiting positive virtues of instability, 7th International Conference on Structural Engineering, Mechanics and Computation (SEMC), Publisher: CRC PRESS-BALKEMA, Pages: 455-461
Villette CC, Phillips ATM, 2018, Rate and age-dependent damage elasticity formulation for efficient hip fracture simulations, Medical Engineering and Physics, Vol: 61, Pages: 1-12, ISSN: 1350-4533
Prediction of bone failure is beneficial in a range of clinical situations from screening of osteoporotic patients with high fracture risk to assessment of protective equipment against trauma. Computational efficiency is an important feature to consider when developing failure models for iterative applications, such as patient-specific diagnosis or design of orthopaedic devices. The authors previously developed a methodology to generate efficient mesoscale structural full bone models. The aim of this study was to implement a damage elasticity formulation representative of an elasto-plastic material model with age and strain rate dependencies compatible with these structural models. This material model was assessed in the prediction of femoral fractures in longitudinal compression and side fall scenarios. The simulations predicted failure loads and fracture patterns in good agreement with reported results from experimental studies. The observed influence of strain rate on failure load was consistent with literature. The superiority of a simplified elasto-plastic formulation over an elasto-brittle bone material model was assessed. This computationally efficient damage elasticity formulation was capable of capturing fracture development after onset.
Kaufmann J, Phillips A, McGregor A, 2018, Investigating bone health in lower-limb amputees, 2018 Blast Injury Conference
Favier C, McGregor A, Phillips A, 2018, Subject specific multiscale modelling of the lumbar spine, 14th Annual Bath Biomechanics Symposium
Verbruggen S, Kainz B, Shelmerdine SC, et al., 2018, Altered biomechanical stimulation of the developing hip joint in presence of hip dysplasia risk factors, Journal of Biomechanics, Vol: 78, Pages: 1-9, ISSN: 0021-9290
Fetal kicking and movements generate biomechanical stimulation in the fetal skeleton, which is important for prenatal musculoskeletal development, particularly joint shape. Developmental dysplasia of the hip (DDH) is the most common joint shape abnormality at birth, with many risk factors for the condition being associated with restricted fetal movement. In this study, we investigate the biomechanics of fetal movements in such situations, namely fetal breech position, oligohydramnios and primiparity (firstborn pregnancy). We also investigate twin pregnancies, which are not at greater risk of DDH incidence, despite the more restricted intra-uterine environment. We track fetal movements for each of these situations using cine-MRI technology, quantify the kick and muscle forces, and characterise the resulting stress and strain in the hip joint, testing the hypothesis that altered biomechanical stimuli may explain the link between certain intra-uterine conditions and risk of DDH. Kick force, stress and strain were found to be significantly lower in cases of breech position and oligohydramnios. Similarly, firstborn fetuses were found to generate significantly lower kick forces than non-firstborns. Interestingly, no significant difference was observed in twins compared to singletons. This research represents the first evidence of a link between the biomechanics of fetal movements and the risk of DDH, potentially informing the development of future preventative measures and enhanced diagnosis. Our results emphasise the importance of ultrasound screening for breech position and oligohydramnios, particularly later in pregnancy, and suggest that earlier intervention to correct breech position through external cephalic version could reduce the risk of hip dysplasia.
Zaharie DZ, Phillips ATM, 2018, Pelvic construct prediction of trabecular and cortical bone structural architecture, Journal of Biomechanical Engineering, Vol: 140, Pages: 1-11, ISSN: 0148-0731
The pelvic construct is an important part of the body as it facilitates the transfer of upper body weight to the lower limbs and protects a number of organs and vessels in the lower abdomen. In addition, the importance of the pelvis is highlighted by the high mortality rates associated with pelvic trauma. This study presents a mesoscale structural model of the pelvic construct and the joints and ligaments associated with it. Shell elements were used to model cortical bone, while truss elements were used to model trabecular bone and the ligaments and joints. The finite element (FE) model was subjected to an iterative optimization process based on a strain-driven bone adaptation algorithm. The bone model was adapted to a number of common daily living activities (walking, stair ascent, stair descent, sit-to-stand, and stand-to-sit) by applying onto it joint and muscle loads derived using a musculoskeletal modeling framework. The cortical thickness distribution and the trabecular architecture of the adapted model were compared qualitatively with computed tomography (CT) scans and models developed in previous studies, showing good agreement. The sensitivity of the model to changes in material properties of the ligaments and joint cartilage and changes in parameters related to the adaptation algorithm was assessed. Changes to the target strain had the largest effect on predicted total bone volumes. The model showed low sensitivity to changes in all other parameters. The minimum and maximum principal strains predicted by the structural model compared to a continuum CT-derived model in response to a common test loading scenario showed good agreement with correlation coefficients of 0.813 and 0.809, respectively. The developed structural model enables a number of applications such as fracture modeling, design, and additive manufacturing of frangible surrogates.
Kaufmann J, Phillips A, McGregor A, 2018, Investigating bone health in lower-limb amputees, 14th Bath Biomechanics Symposium
Favier C, McGregor A, Phillips A, 2018, Combined musculoskeletal and structural finite element modelling of the lumbar spine, 8th World Congress of Biomechanics
Kaufmann J, Phillips A, McGregor A, 2018, Investigating bone health in lower-limb amputees, Virtual Physiological Human 2018 Congress
Gillie M, Phillips A, 2018, Teaching creative structural design - Seminar, IABSE Conference Bath 2017 - Creativity and Collaboration, Pages: 33-34
This seminar will examine how teaching structural design to encourage creativity is best approached. It will consist of four short presentations from different perspectives, followed by a facilitated discussion aimed at provoking debate.
Bellamy L, Phillips A, Ward J, 2018, Optimisation of structural form based on multiple sustainability factors, IABSE Conference Bath 2017, Pages: 119-120
Structural design and analysis is dependent on optimisation approaches. However, such optimisation is mostly performed for the permanent structure and constructability is rarely considered at the design stages. The goal of the research presented here is to develop a digital design process that encompasses constructability and sustainability factors. The initial process uses common methods for cross-sectional, structural arrangement and structural form optimisation in an automated fashion and facilitates software packages to work together. Further development will enable the process to optimise the structure across construction stages.
Verbruggen S, Kainz B, Shelmerdine S, et al., 2018, Stresses and strains on the human fetal skeleton during development, Journal of the Royal Society Interface, Vol: 15, Pages: 1-11, ISSN: 1742-5662
Mechanical forces generated by fetal kicks and movements result in stimulation of the fetal skeleton in the form of stress and strain. This stimulation is known to be critical for prenatal musculoskeletal development; indeed, abnormal or absent movements have been implicated in multiple congenital disorders. However, the mechanical stress and strain experienced by the developing human skeleton in utero have never before been characterized. Here, we quantify the biomechanics of fetal movements during the second half of gestation by modelling fetal movements captured using novel cine-magnetic resonance imaging technology. By tracking these movements, quantifying fetal kick and muscle forces, and applying them to three-dimensional geometries of the fetal skeleton, we test the hypothesis that stress and strain change over ontogeny. We find that fetal kick force increases significantly from 20 to 30 weeks' gestation, before decreasing towards term. However, stress and strain in the fetal skeleton rises significantly over the latter half of gestation. This increasing trend with gestational age is important because changes in fetal movement patterns in late pregnancy have been linked to poor fetal outcomes and musculoskeletal malformations. This research represents the first quantification of kick force and mechanical stress and strain due to fetal movements in the human skeleton in utero, thus advancing our understanding of the biomechanical environment of the uterus. Further, by revealing a potential link between fetal biomechanics and skeletal malformations, our work will stimulate future research in tissue engineering and mechanobiology.
Villette CC, Castilho M, Malda J, et al., 2017, Heterogeneous design optimisation of tissue engineering scaffolds: in-vitro assessment of a digital design framework, 15th International Symposium on Computer Methods in Biomechanics and Biomedical Engineering, Publisher: Taylor & Francis, ISSN: 1025-5842
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