Material Properties of the Intervertebral Disc

Lead Research Organisation: Imperial College London
Department Name: Dept of Bioengineering

Abstract

The intervertebral disc is the primary articulation between adjacent vertebral bodies in the human spine. Degenerative disc disease is the leading cause of pain and disability in the adult; replacing the diseased disc with an artificial material is becoming the treatment of choice in cases that require surgery. At the same time, injuries to the spinal column are common in incidents that are associated with high accelerations, such as falls, sports injuries, road traffic accidents, and acts of violence; these injuries are often associated with long term disability. Injury induced by road-traffic accidents alone is predicted to become the third leading cause for burden of disease by 2030 according to the World Health Organization.

A comprehensive understanding of the mechanisms associated with injury to the spine is lacking, especially in high-energy trauma. Official NATO reports acknowledge the limitations of current injury criteria and lack of injury risk curves for the spine; these criteria and curves would allow us to evaluate vehicles and protection systems appropriately. Similarly, the human-like response of anthropometric test devices (or dummies) in predicting the response of the human spine under load is questionable. As a result, strategies to enhance protection and to improve protective equipment are being developed using sub-standard technologies.

Finite element (FE) modelling - a type of computer simulation of the mechanics of structures - of human injury, of implants and of protective systems are important engineering tools that allow us to understand the mechanisms involved in an injurious event and to develop new and improved evaluation criteria, techniques, materials and designs in a cost-efficient manner. As computational power becomes more abundant, FE modelling for optimal design is a clear strategic direction in industry as an alternative to expensive and labour intensive experiments. A critical parameter, however, that influences the predictive ability of FE models of human response is the quality of the input data that are associated with the material behaviour of human tissue. Such data, particularly at loading rates relevant to injury, are sparse for most human tissues; this is definitely the case for the intervertebral disc.

The aim of this project, therefore, is to quantify the material behaviour of the human intervertebral disc across physiological and injurious loading rates. The intention is to inform implant design and to increase the accuracy of FE models of human injury in order to improve their ability to simulate the response of the spine under load.

Planned Impact

The ultimate beneficiary of this work is the patient with spinal injury, and society and economy through prevention of spinal injury.
The main, direct beneficiaries of this work are researchers and industry that develop computer (specifically, finite element) models of the spine to predict joint motion, loading, and potential for injury in order to enable the design of better surgical interventions, safety systems, personal protection equipment and other mitigation technologies. Better protection from, and better surgical reconstruction of, spinal injury have a clear, direct economic and societal impact through reduction of healthcare costs and improvement in quality of life. The impact is not only due to the fewer injured people, but also due to the use of more efficient means of design for protection. The work can contribute to impact at the long term in goverment policy and international standards in orthopaedic, automotive and military domains.

The proposed research will achieve its impact by the implementation of a material model of the intervertebral disc (IVD) into finite element (FE) models of the spine, and by informing the selection of materials for use in IVD implants. It will also achieve impact when the software program that will be developed as part of this work is taken upon by other researchers or industry for application in characterisation of human tissue or other materials and physical processes.

Dissemination of the outcomes of this work to the beneficiaries will be achieved primarily through presentations at appropriate scientific conferences, publication in peer-reviewed journals with appropriate readership, and personal communications to the industrial stakeholders. Direct communication to the immediate beneficiaries - both academic and industrial - will ensure that there is immediate impact at the end of the grant period.

Furthermore, I am part of the The Royal British Legion (TRBL) Centre for Blast Injury Studies at Imperial, a very high-visibility 'project' for both Imperial and TRBL. This partnership, among others, is ensuring avenues for technology transfer and public engagement. For example, the Centre publishes an annual report that is available to download freely from the website. This activity ensures that the work is communicated appropriately to the public.

Publications

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Draper D (2021) Multiscale Validation of Multiple Human Body Model Functional Spinal Units. in Journal of biomechanical engineering

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Masouros S (2017) Spinal Injury in Impact

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Newell N (2017) Material properties of bovine intervertebral discs across strain rates. in Journal of the mechanical behavior of biomedical materials

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Newell N (2019) Material properties of human lumbar intervertebral discs across strain rates. in The spine journal : official journal of the North American Spine Society

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Newell N (2017) Biomechanics of the human intervertebral disc: A review of testing techniques and results. in Journal of the mechanical behavior of biomedical materials

 
Description The objective was to obtain material properties of the intervertebral disc across loading rates using a combined experimental - numerical approach.
We have completed the work on bovine tissue and on human tissue and published. We also did satellite studies, one of which was to ascertain the role of the nucleus pulposus (the gel-like middle part of the disc) in transferring mechanical loads; we found that, contrary to what was thought previously, the nucleus does not carry any load and its role is probably mostly related to biological and nutritional aspects.
Exploitation Route The data are publicly available and the methodology by which we derived the material properties of the disc are published.
The results can be used readily in computational models of spinal segments or the whole spine and in selecting materials for implants.
The methodology can be used to derive material properties of other complex tissues whereby direct testing of coupons is not possible.
Sectors Healthcare,Manufacturing, including Industrial Biotechology,Pharmaceuticals and Medical Biotechnology

URL http://www.sciencedirect.com/science/article/pii/S1751616116303095
 
Description The experiments we conducted have been used by organisations in Europe who work on the improvement of human body models used for road traffic accident simulations by the automotive industry.
First Year Of Impact 2018
Sector Manufacturing, including Industrial Biotechology
Impact Types Economic

 
Description Injury & Reconstruction Biomechanics Test Suite
Amount £1,281,962 (GBP)
Funding ID EP/S021752/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 01/2019 
End 12/2023
 
Description Use of our experimental data for validation of human body models 
Organisation Ludwig Maximilian University of Munich (LMU Munich)
Country Germany 
Sector Academic/University 
PI Contribution We provided the experimental data for validation of a variety of human body models used in road-traffic accident research and by automotive OEMs
Collaborator Contribution They are running the human body models to which we don't have access.
Impact One publication in a conference (IRCOBI 2018) and another one being prepared
Start Year 2017
 
Description behaviour of the disc 
Organisation University of Bristol
Department School of Chemistry
Country United Kingdom 
Sector Academic/University 
PI Contribution worked together on a review paper
Collaborator Contribution worked together on a review paper
Impact review article publication
Start Year 2016
 
Description disc behaviour 
Organisation Queensland University of Technology (QUT)
Department Paediatric Spine Research Group
Country Australia 
Sector Hospitals 
PI Contribution worked together on a review article.
Collaborator Contribution worked together on a review article. Shared their technology on semi-automated mesh generation of spinal units.
Impact We published a review article together in JMBBM, http://www.sciencedirect.com/science/article/pii/S1751616117300449
Start Year 2016