Ifsttar PhD subject

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Title : Modelling the postural changes in the spine for applications in biomechanics

Main host Laboratory - Referent Advisor TS2 - LBMC  -  LAFON-JALBY Yoann      tél. : +33 472655476/ 06 07 06 22 51

Director of the main host Laboratory MITTON David  -

PhD Speciality mécanique, biomécanique

Axis of the performance contract 1 - COP2017 - Efficient transport and safe travel

Main location Bron

Doctoral affiliation UNIVERSITE CLAUDE-BERNARD-LYON 1

PhD school MEGA (MECANIQUE, ENERGETIQUE, GENIE CIVIL, ACOUSTIQUE)

Planned PhD supervisor BEILLAS Philippe  -  Université Gustave Eiffel  -  TS2 - LBMC

Planned PhD co-supervisor LAFON-JALBY Yoann  -    -

Planned financing Contrat doctoral  - Ifsttar

Abstract

Context:
Often based on the finite element (FE) method, numerical models of the spine are currently used in multiple biomechanical domains of applications. For example:
• For orthopaedics, to study of the fusion of lumbar [9], cervical [8] or sacro-iliac segments [7] in case of spinal instability or low back pain.
• For ergonomics and work safety, to estimate the pressure in the intervertebral discs and the risk of pain [2, 4] due to repetitive loading at work or during transportation (e.g. Norm ISO 2631-5 2018).
• For crash, to study the risk of lumbar injury that could be associated to new postures in future automated vehicle and more generally to investigate the risk of submarining (e.g. [5]). The LBMC is currently active on lumbar spine modelling for the GHBMC (www.ghbmc.com).

In all these cases, the spine posture is an important biomechanical parameter. For orthopaedics, it affects the sagittal balance/postural compensation after spine fixation to avoid low back pain [6]. For health safety, the ISO 2631-5 2018 norm suggest an effect of posture on the risk and attempts to account for it. For crash, a more relaxed /slouched lumbar posture increases the submarining risk (e.g. [5]) and posture also affects the fracture tolerance and pattern [3].

However, if the posture associated with various activities has been widely studied and predicting methods have been developed (e.g. [10]), posture change and its biomechanics are not well accounted for in the FE models. There is a lack of knowledge on:
• The mechanical state of the anatomical structure of the spine: the posture is expected to affect the initial strain and tension in the ligaments and fibres of the intervertebral disk, the loading of apophyseal joints as well as the remaining range of motion before failure in case of extreme loading. However, limited experimental data are available.
• How to account for these initial state changes in the models (e.g. though changes of material parameters, initial strain or stress, etc.), and how a model should be designed and validated to account for those.
• Numerical methodologies to change the posture of deformable FE models, which are much more complex than for rigid multi-body models. Furthermore, the mesh of the surrounding structures (discs, organs, soft tissues etc.) must follow the change while keeping an acceptable element quality. This makes the posture change difficult for most users especially, even with recent efforts on this topic (including the PIPER open source tools in which the LBMC is actively involved, www.piper-project.org).

As a consequence, simulations are often performed in postures that do not match the experimental reference and initial strains and stresses are typically neglected. This limits the prediction capability of the models related to comfort, implant failure, disc degeneration, and injury risk. This was recently illustrated for the neck by Boakye-Yadom et al. (2018) [1].

Objectives
The research will aim to improve the spinal models by better accounting for positional changes. It will focus on the lumbar spine and include models within full body models.
It will include work on both knowledge gaps (e.g. on the initial tissue states) and methodological gaps (e.g. on the positioning and initial mechanical state modelling).
The results will improve the spine model predictions for a wide range of domains. Applications in comfort/health safety, crash and orthopaedics will serve as demonstrators to develop the methodologies.

Approach
The approach will combine experimental, simulation and software work.
An experimental study will be conducted on isolated spine specimens to assess the mechanical state of the spine components (e.g. ligaments, discs) as a function of posture. This will be facilitated by the use of a robotic arm to apply and reproduce accurately various postures. Local measurements methods (e.g. strain gages, pressure, surface strain) will be considered as well. The study will be prepared using sensitivity analyses on existing FE models available at the laboratory (GHBMC and PIPER models).
The tests will be simulated using personalized models adapted from the PIPER spine model. This model will be improved to facilitate its personalization and its positioning. Various modelling approaches to account for the initial state in the tissues will be compared and used in three test cases related to:
(1) back pain predictions (scenario: repetitive loading for a bus driver due to speed bumps and comparison with the ISO 2631-5 norm on the risk prediction),
(2) impact (scenario: effect of the posture modelling on the predicted injury risk in the case of semi reclined passengers),
(3) orthopaedics (scenario to be confirmed: reproduction of the spine posture after lumbar fixation surgery based on pre/post-operative EOS imaging).

Personalizing and positioning of the spine models will be performed using the PIPER software tool. Improvements will be made if required in particular to better constrain (1) the spine curvature and the pelvic tilt in the positioning tool and (2) the volume of soft tissues during positioning.

The work will use results and tools available at LBMC (e.g. models and expertise of them, PIPER tools, robotic arm, application scenarios, etc.) such that the research can focus on the posture modelling.

Expected results
The improvement of the model prediction capability will be illustrated in three test cases. Besides, the research will lead to:
• New knowledge and data regarding initial strain / stresses that can be used for model assessment,
• Recommendations to model the initial posture (geometrical and mechanical aspects) and a personalizable lumbar spine model, implementing these (open source license).
• Improvements of the PIPER tools for spine positioning (also released as Open Source).
Each of these may result in a separate publication.

Scientific skills after the thesis
The candidate will acquire both knowledge and methodologies applicable to several biomechanics related fields (crash, ergonomics, and orthopaedics), on both numerical and experimental aspects.

Disciplines
The major field will be mechanical engineering, with a numerical and experimental components. Numerical methods and computer science will be a secondary field.

Expected profile
Ideally, the candidate will have a degree in mechanical engineering, an experience in simulation work and a strong interest for numerical and experimental biomechanics. An interest in programming (C++) would be a plus.
A candidate with training in computer science and a strong interest for biomechanics may also be considered.

Supervising team
It will be composed of Yoann Lafon (Assistant Professor, biomechanics for orthopedics, numerical methods, personalization of FE models) and Philippe Beillas (Research Director, HDR, numerical and experimental impact biomechanics, leading the PIPER project and the GHBMC lumbar and abdomen development). On the experimental aspects, it will be reinforced by Bertrand Fréchède (Assistant Professor) who developed testing methodologies for the spine based on the control of a robotic arm. Collaboration with a PhD student in comfort modeling supervised by Xuguang Wang (Ifsttar Research Director) will be possible. A collaboration with the team “imaging and personalization” from LIA EVASYM (coll. Lyon-Montréal) is considered for the Orthopaedics/Health test case. Finally Bertrand Richard (Software Research Engineer) will be involved on the programming and software aspects of the project.

References
[1] Boakye-Yiadom S, et al (2018) On the importance of retaining stresses and strains in repositioning computational biomechanical models of the cervical spine. Int. J. for Num. Meth. in Biomed. Eng., 34(1).
[2] Claus et al. (2008) Sitting versus standing: Does the intradiscal pressure cause disc degeneration or low back pain? J of Electromyography and Kinesiology, 18(4) 550-558.
[3] Curry, et al. (2016) Lumbar spine endplate fractures: Biomechanical evaluation and clinical considerations through experimental induction of injury. J. of Orthopaedic Research, 34(6), 1084–1091.
[4] Dreischarf et al. (2016) Estimation of loads on human lumbar spine: A review of in vivo and computational model studies. J Biomech. 11;49(6):833-845.
[5] Grébonval et al. (2019) Occupant response in frontal crash, after alterations of the standard driving position. Ircobi Conf. Florence, Italy.
[6] Le Huec et al. (2015) Evidence showing the relationship between sagittal balance and clinical outcomes in surgical treatment of degenerative spinal diseases: a literature review. Int Orthop. 39(1):87-95.
[7] Lindsey et al. (2018) Sacroiliac joint stability: Finite element analysis of implant number, orientation, and superior implant length. World J Orthop. 9(3): 14-23.
[8] Mackiewicz et al. (2016) Comparative studies of cervical spine anterior stabilization systems--Finite element analysis. Clin Biomech Feb;32:72-9.
[9] Más et al. (2017) Finite element simulation and clinical follow-up of lumbar spine biomechanics with dynamic fixations. PLoS ONE 12(11).
[10] Nerot et al. (2016) A Principal Component Analysis of the Relationship between the External Body Shape and Internal Skeleton for the Upper Body. J. of Biomech. 49, no. 14.

Keywords : Mechanical engineering, biomechanics, computer science, lumbar spine, Safety, Ergonomics, Health

Main host Laboratory - Referent Advisor	TS2 - LBMC - LAFON-JALBY Yoann tél. : +33 472655476/ 06 07 06 22 51
Director of the main host Laboratory	MITTON David -
PhD Speciality	mécanique, biomécanique
Axis of the performance contract	1 - COP2017 - Efficient transport and safe travel
Main location	Bron
Doctoral affiliation	UNIVERSITE CLAUDE-BERNARD-LYON 1
PhD school	MEGA (MECANIQUE, ENERGETIQUE, GENIE CIVIL, ACOUSTIQUE)
Planned PhD supervisor	BEILLAS Philippe - Université Gustave Eiffel - TS2 - LBMC
Planned PhD co-supervisor	LAFON-JALBY Yoann - -
Planned financing	Contrat doctoral - Ifsttar
Abstract Context: Often based on the finite element (FE) method, numerical models of the spine are currently used in multiple biomechanical domains of applications. For example: • For orthopaedics, to study of the fusion of lumbar [9], cervical [8] or sacro-iliac segments [7] in case of spinal instability or low back pain. • For ergonomics and work safety, to estimate the pressure in the intervertebral discs and the risk of pain [2, 4] due to repetitive loading at work or during transportation (e.g. Norm ISO 2631-5 2018). • For crash, to study the risk of lumbar injury that could be associated to new postures in future automated vehicle and more generally to investigate the risk of submarining (e.g. [5]). The LBMC is currently active on lumbar spine modelling for the GHBMC (www.ghbmc.com). In all these cases, the spine posture is an important biomechanical parameter. For orthopaedics, it affects the sagittal balance/postural compensation after spine fixation to avoid low back pain [6]. For health safety, the ISO 2631-5 2018 norm suggest an effect of posture on the risk and attempts to account for it. For crash, a more relaxed /slouched lumbar posture increases the submarining risk (e.g. [5]) and posture also affects the fracture tolerance and pattern [3]. However, if the posture associated with various activities has been widely studied and predicting methods have been developed (e.g. [10]), posture change and its biomechanics are not well accounted for in the FE models. There is a lack of knowledge on: • The mechanical state of the anatomical structure of the spine: the posture is expected to affect the initial strain and tension in the ligaments and fibres of the intervertebral disk, the loading of apophyseal joints as well as the remaining range of motion before failure in case of extreme loading. However, limited experimental data are available. • How to account for these initial state changes in the models (e.g. though changes of material parameters, initial strain or stress, etc.), and how a model should be designed and validated to account for those. • Numerical methodologies to change the posture of deformable FE models, which are much more complex than for rigid multi-body models. Furthermore, the mesh of the surrounding structures (discs, organs, soft tissues etc.) must follow the change while keeping an acceptable element quality. This makes the posture change difficult for most users especially, even with recent efforts on this topic (including the PIPER open source tools in which the LBMC is actively involved, www.piper-project.org). As a consequence, simulations are often performed in postures that do not match the experimental reference and initial strains and stresses are typically neglected. This limits the prediction capability of the models related to comfort, implant failure, disc degeneration, and injury risk. This was recently illustrated for the neck by Boakye-Yadom et al. (2018) [1]. Objectives The research will aim to improve the spinal models by better accounting for positional changes. It will focus on the lumbar spine and include models within full body models. It will include work on both knowledge gaps (e.g. on the initial tissue states) and methodological gaps (e.g. on the positioning and initial mechanical state modelling). The results will improve the spine model predictions for a wide range of domains. Applications in comfort/health safety, crash and orthopaedics will serve as demonstrators to develop the methodologies. Approach The approach will combine experimental, simulation and software work. An experimental study will be conducted on isolated spine specimens to assess the mechanical state of the spine components (e.g. ligaments, discs) as a function of posture. This will be facilitated by the use of a robotic arm to apply and reproduce accurately various postures. Local measurements methods (e.g. strain gages, pressure, surface strain) will be considered as well. The study will be prepared using sensitivity analyses on existing FE models available at the laboratory (GHBMC and PIPER models). The tests will be simulated using personalized models adapted from the PIPER spine model. This model will be improved to facilitate its personalization and its positioning. Various modelling approaches to account for the initial state in the tissues will be compared and used in three test cases related to: (1) back pain predictions (scenario: repetitive loading for a bus driver due to speed bumps and comparison with the ISO 2631-5 norm on the risk prediction), (2) impact (scenario: effect of the posture modelling on the predicted injury risk in the case of semi reclined passengers), (3) orthopaedics (scenario to be confirmed: reproduction of the spine posture after lumbar fixation surgery based on pre/post-operative EOS imaging). Personalizing and positioning of the spine models will be performed using the PIPER software tool. Improvements will be made if required in particular to better constrain (1) the spine curvature and the pelvic tilt in the positioning tool and (2) the volume of soft tissues during positioning. The work will use results and tools available at LBMC (e.g. models and expertise of them, PIPER tools, robotic arm, application scenarios, etc.) such that the research can focus on the posture modelling. Expected results The improvement of the model prediction capability will be illustrated in three test cases. Besides, the research will lead to: • New knowledge and data regarding initial strain / stresses that can be used for model assessment, • Recommendations to model the initial posture (geometrical and mechanical aspects) and a personalizable lumbar spine model, implementing these (open source license). • Improvements of the PIPER tools for spine positioning (also released as Open Source). Each of these may result in a separate publication. Scientific skills after the thesis The candidate will acquire both knowledge and methodologies applicable to several biomechanics related fields (crash, ergonomics, and orthopaedics), on both numerical and experimental aspects. Disciplines The major field will be mechanical engineering, with a numerical and experimental components. Numerical methods and computer science will be a secondary field. Expected profile Ideally, the candidate will have a degree in mechanical engineering, an experience in simulation work and a strong interest for numerical and experimental biomechanics. An interest in programming (C++) would be a plus. A candidate with training in computer science and a strong interest for biomechanics may also be considered. Supervising team It will be composed of Yoann Lafon (Assistant Professor, biomechanics for orthopedics, numerical methods, personalization of FE models) and Philippe Beillas (Research Director, HDR, numerical and experimental impact biomechanics, leading the PIPER project and the GHBMC lumbar and abdomen development). On the experimental aspects, it will be reinforced by Bertrand Fréchède (Assistant Professor) who developed testing methodologies for the spine based on the control of a robotic arm. Collaboration with a PhD student in comfort modeling supervised by Xuguang Wang (Ifsttar Research Director) will be possible. A collaboration with the team “imaging and personalization” from LIA EVASYM (coll. Lyon-Montréal) is considered for the Orthopaedics/Health test case. Finally Bertrand Richard (Software Research Engineer) will be involved on the programming and software aspects of the project. References [1] Boakye-Yiadom S, et al (2018) On the importance of retaining stresses and strains in repositioning computational biomechanical models of the cervical spine. Int. J. for Num. Meth. in Biomed. Eng., 34(1). [2] Claus et al. (2008) Sitting versus standing: Does the intradiscal pressure cause disc degeneration or low back pain? J of Electromyography and Kinesiology, 18(4) 550-558. [3] Curry, et al. (2016) Lumbar spine endplate fractures: Biomechanical evaluation and clinical considerations through experimental induction of injury. J. of Orthopaedic Research, 34(6), 1084–1091. [4] Dreischarf et al. (2016) Estimation of loads on human lumbar spine: A review of in vivo and computational model studies. J Biomech. 11;49(6):833-845. [5] Grébonval et al. (2019) Occupant response in frontal crash, after alterations of the standard driving position. Ircobi Conf. Florence, Italy. [6] Le Huec et al. (2015) Evidence showing the relationship between sagittal balance and clinical outcomes in surgical treatment of degenerative spinal diseases: a literature review. Int Orthop. 39(1):87-95. [7] Lindsey et al. (2018) Sacroiliac joint stability: Finite element analysis of implant number, orientation, and superior implant length. World J Orthop. 9(3): 14-23. [8] Mackiewicz et al. (2016) Comparative studies of cervical spine anterior stabilization systems--Finite element analysis. Clin Biomech Feb;32:72-9. [9] Más et al. (2017) Finite element simulation and clinical follow-up of lumbar spine biomechanics with dynamic fixations. PLoS ONE 12(11). [10] Nerot et al. (2016) A Principal Component Analysis of the Relationship between the External Body Shape and Internal Skeleton for the Upper Body. J. of Biomech. 49, no. 14.
Keywords :	Mechanical engineering, biomechanics, computer science, lumbar spine, Safety, Ergonomics, Health

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