title: Bovine and degenerated human annulus fibrosus: a microstructural and micromechanical comparison.
abstract: The complex structure of the annulus fibrosus is strongly related to its mechanical properties. Recent work showed that it is possible to observe the relative movement of fibre bundles in loaded cow tail annulus; the aim of this work was to describe and quantify annulus fibrosus micromechanics in degenerated human disc, and compare it with cow tail annulus, an animal model often used in the literature. Second harmonic generation was used to image the collagen matrix in twenty strips of annulus fibrosus harvested from intervertebral disc of seven patients undergoing surgery. Samples were loaded to 6% tensile strain in 1% steps. Elastic modulus was calculated from loading curves, and micromechanical strains were calculated from the images using custom software. The same protocol was applied to twenty strips of annulus harvested from cow tail discs. Significant morphological differences were found between human and cow tail samples, the most striking being the lack of collagen fibre crimp in the former. Fibres were also observed bending and running from one lamella to the other, forming a strong flexible interface. Interdigitation of fibre bundles was also present at this interface. Quantitative results show complex patterns of inter-bundle and inter-lamellar behaviour, with inter-bundle sliding being the main strain mechanism. Elastic modulus was similar between species, and it was not affected by the degree of degeneration. This work gives an insight into the complex structure and mechanical function of the annulus fibrosus, which should be accounted for in disc numerical modelling.
authors.affiliation: School of Physics and Astronomy, University of Exeter, Physics Building, Stocker Road, Exeter, EX4 4QL, UK. c.vergari@gmail.com.
authors.forename: Claudio
authors.identifier: 0000-0002-7049-2405
authors.initials: C
authors.lastname: Vergari
authors.affiliation: Peninsula Spine Unit, Princess Elizabeth Orthopaedic Centre, Royal Devon and Exeter Hospital, Barrack Road, Exeter, Devon, EX2 5DW, UK.
authors.forename: Daniel
authors.initials: D
authors.lastname: Chan
authors.affiliation: Peninsula Spine Unit, Princess Elizabeth Orthopaedic Centre, Royal Devon and Exeter Hospital, Barrack Road, Exeter, Devon, EX2 5DW, UK.
authors.forename: Andrew
authors.initials: A
authors.lastname: Clarke
authors.affiliation: School of Physics and Astronomy, University of Exeter, Physics Building, Stocker Road, Exeter, EX4 4QL, UK.
authors.forename: Jessica C
authors.initials: JC
authors.lastname: Mansfield
authors.affiliation: School of Physics and Astronomy, University of Exeter, Physics Building, Stocker Road, Exeter, EX4 4QL, UK.
authors.forename: Judith R
authors.initials: JR
authors.lastname: Meakin
authors.affiliation: School of Physics and Astronomy, University of Exeter, Physics Building, Stocker Road, Exeter, EX4 4QL, UK.
authors.forename: Peter C
authors.initials: PC
authors.lastname: Winlove
mesh_terms: D000818:Animals; D000070616:Annulus Fibrosus / Q000166:cytology / Q000473:pathology* / Q000648:ultrastructure; D002417:Cattle; D003094:Collagen / Q000032:analysis; D055119:Elastic Modulus; D006801:Humans; D055959:Intervertebral Disc Degeneration / Q000473:pathology; D008954:Models, Biological; D012984:Software
chemical_list: D003094:Collagen
keywords: Crimps; Fibres; Intervertebral disc; Second harmonic generation