title: Collagen Organization in Facet Capsular Ligaments Varies With Spinal Region and With Ligament Deformation.
abstract: The spinal facet capsular ligament (FCL) is primarily comprised of heterogeneous arrangements of collagen fibers. This complex fibrous structure and its evolution under loading play a critical role in determining the mechanical behavior of the FCL. A lack of analytical tools to characterize the spatial anisotropy and heterogeneity of the FCL's microstructure has limited the current understanding of its structure-function relationships. Here, the collagen organization was characterized using spatial correlation analysis of the FCL's optically obtained fiber orientation field. FCLs from the cervical and lumbar spinal regions were characterized in terms of their structure, as was the reorganization of collagen in stretched cervical FCLs. Higher degrees of intra- and intersample heterogeneity were found in cervical FCLs than in lumbar specimens. In the cervical FCLs, heterogeneity was manifested in the form of curvy patterns formed by collections of collagen fibers or fiber bundles. Tensile stretch, a common injury mechanism for the cervical FCL, significantly increased the spatial correlation length in the stretch direction, indicating an elongation of the observed structural features. Finally, an affine estimation for the change of correlation length under loading was performed which gave predictions very similar to the actual values. These findings provide structural insights for multiscale mechanical analyses of the FCLs from various spinal regions and also suggest methods for quantitative characterization of complex tissue patterns.
authors.affiliation: Department of Materials Science and Engineering, University of Pennsylvania, 211 LRSM, 3231 Walnut Street, Philadelphia, PA 19104 e-mail: ehsan.ban@gmail.com.
authors.forename: Ehsan
authors.initials: E
authors.lastname: Ban
authors.affiliation: Department of Bioengineering, University of Pennsylvania, 240 Skirkanich Hall, 210 S. 33rd Street, Philadelphia, PA 19104 e-mail: sijiaz@seas.upenn.edu.
authors.forename: Sijia
authors.initials: S
authors.lastname: Zhang
authors.affiliation: Department of Mechanical Engineering, University of Minnesota-Twin Cities, 7-105 Nils Hasselmo Hall, 312 Church Street SE, Minneapolis, MN 55455 e-mail: zarei004@umn.edu.
authors.forename: Vahhab
authors.initials: V
authors.lastname: Zarei
authors.affiliation: Department of Biomedical Engineering, University of Minnesota-Twin Cities, 7-105 Nils Hasselmo Hall, 312 Church Street SE, Minneapolis, MN 55455 e-mail: baroc001@umn.edu.
authors.forename: Victor H
authors.initials: VH
authors.lastname: Barocas
authors.affiliation: Departments of Bioengineering and Neurosurgery, University of Pennsylvania, 240 Skirkanich Hall, 210 South 33rd Street, Philadelphia, PA 19104 e-mail: winkelst@seas.upenn.edu.
authors.forename: Beth A
authors.initials: BA
authors.lastname: Winkelstein
authors.affiliation: Department of Mechanical, Aerospace, and Nuclear Engineering, Rensselaer Polytechnic Institute, 2048 Jonsson Engineering Center, 110 8th Street, Troy, NY 12180 e-mail: picuc@rpi.edu.
authors.forename: Catalin R
authors.initials: CR
authors.lastname: Picu
mesh_terms: D002574:Cervical Vertebrae; D003094:Collagen / Q000378:metabolism*; D005260:Female; D006801:Humans; D017746:Joint Capsule / Q000166:cytology / Q000378:metabolism*; D008023:Ligaments, Articular / Q000033:anatomy & histology* / Q000166:cytology / Q000378:metabolism*; D008159:Lumbar Vertebrae; D008297:Male; D008875:Middle Aged; D057054:Molecular Imaging
chemical_list: D003094:Collagen