A full-field 3D digital image correlation and modelling technique to characterise anterior cruciate ligament mechanics ex vivo

Readioff, Rosti; Geraghty, Brendan; Comerford, Eithne; Elsheikh, Ahmed

Affiliations

¹School of Engineering, University of Liverpool, Liverpool L69 3GH, UK

²Institute of Life Course and Medical Sciences, University of Liverpool, William Henry Duncan Building, 6 West Derby Street, L7 8TX, UK

³Institute of Veterinary Science, Leahurst Campus, University of Liverpool, Chester High road, Neston CH64 7TE, UK

⁴Beijing Advanced Innovation Center for Biomedical Engineering, Beihang University, Beijing 100083, China

⁵NIHR Moorfields BRC, 2/12 Wolfson Building, UCL Institute of Ophthalmology, 11-43 Bath Street, London, EC1V 9EL, UK

Abstract and keywords

It is limiting to use conventional methods when characterising material properties of complex biological tissues with inhomogeneous and anisotropic structure, such as the anterior cruciate ligament (ACL) in the knee joint. This study aims to develop and utilise a three-dimensional digital image correlation method (3D DIC) for the purpose of determining material properties of femur-ACL-tibia complex across the surface without any contact between the tissue and the loading equipment. A full-field (360° view) 3D DIC test setup consisting of six digital single-lens reflex cameras was developed and ACL specimens from skeletally mature dog knee joints were tested. The six cameras were arranged into three pairs and the cameras within each pair were positioned with 25° in between to obtain the desired stereovision output. The test setup was calibrated twice: first to obtain the intrinsic and extrinsic parameters within camera pairs, and second to align the 3D surfaces from each camera pair in order to generate the full view of the ACLs. Using the undeformed 3D surfaces of the ligaments, ACL-specific finite element models were generated. Longitudinal deformation of ligaments under tensile loads obtained from the 3D DIC, and this was analysed to serve as input for the inverse finite element analysis. As a result, hyperelastic coefficients from the first-order Ogden model that characterise ACL behaviour were determined with a marginal error of <1.5%. This test setup and methodology provides a means to accurately determine inhomogeneous and anisotropic material properties of ACL. The methodology described in this study could be adopted to investigate other biological and cultured tissues with complex structure.

Statement of Significance: Determining the material properties of soft tissues with complex anatomical structure, such as the anterior cruciate ligament (ACL), is important to better understand their contribution to musculoskeletal biomechanics. Current conventional methods for characterising material properties of the ACL are often limited to a contact measurement approach, however an improved understanding of the mechanics of this complex tissue is vital in terms of preventing injury and developing novel therapies. This article reports the development and utilisation of non-contact optical methodology involving full-field three-dimensional digital image correlation and finite element analysis to accurately investigate material properties of the ACL, in a controlled environment. This technique reduces inaccuracies due to specimen clamping and more importantly considers the inhomogeneous nature of the examined tissue.

Keywords: Anterior cruciate ligament; Three-dimensional digital image correlation; Finite element model; Inverse finite element analysis; Viscoelastic properties

Links

DOI: 10.1016/j.actbio.2020.07.003

PubMed: 32652225

WoS: 000558174200031

History

Received: 2020-03-29

Revised: 2020-07-01

Accepted: 2020-07-02

Online: 2020-07-08

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Cited By (1)

Year	Entry
2021	Zaylor W. A Framework to Estimate Prestrain in Spring and Continuum Representations of Knee Ligaments [PhD thesis]. Cleveland State University; August 2021.