title: Optical Coherence Tomographic Elastography Reveals Mesoscale Shear Strain Inhomogeneities in the Annulus Fibrosus.
abstract: METHODS
  Basic science study using in vitro tissue testing and imaging to characterize local strains in annulus fibrosus (AF) tissue.
  
  
  OBJECTIVE
  To characterize mesoscale strain inhomogeneities between lamellar and inter-/translamellar (ITL) matrix compartments during tissue shear loading.
  
  
  BACKGROUND
  The intervertebral disc is characterized by significant heterogeneities in tissue structure and plays a critical role in load distribution and force transmission in the spine. In particular, the AF possesses a lamellar architecture interdigitated by a complex network of extracellular matrix components that form a distinct ITL compartment. Currently, there is not a firm understanding of how the lamellar and ITL matrix coordinately support tissue loading.
  
  
  METHODS
  AF tissue samples were prepared from frozen porcine lumbar spines and mounted onto custom fixtures of a materials testing system that incorporates optical coherence tomography (OCT) imaging to perform tissue elastography. Tissues were subjected to 20 and 40% nominal shear strain, and OCT images were captured and segmented to identify regions of interest corresponding to lamellar and ITL compartments. Images were analyzed using an optical flow algorithm to quantify local shear strains within each compartment.
  
  
  RESULTS
  Using histology and OCT, we first verified our ability to visualize and discriminate the ITL matrix from the lamellar matrix in porcine AF tissues. Local AF strains in the ITL compartment (22.0 ± 13.8, 31.1 ± 16.9 at 20% and 40% applied shear, respectively) were significantly higher than corresponding strains in the surrounding lamellar compartment (12.1 ± 5.6, 15.3 ± 5.2) for all tissue samples (P < 0.05).
  
  
  CONCLUSIONS
  Results from this study demonstrate that the lamellar and ITL compartments of the AF distribute strain unevenly during tissue loading. Specifically, shear strain is significantly higher in the ITL matrix, suggesting that these regions may be more susceptible to tissue damage and more mechanobiologically active.
  
  
  METHODS
  N/A.
authors: Fischell Department of Bioengineering, University of Maryland, College Park, MD.|Advanced Biomedical and Smart Welfare Technology R&BD Group, Korea Institute of Industrial Technology, Cheonan, Chungnam, South Korea.
authors: Sang K
authors: SK
authors: Han
authors: Fischell Department of Bioengineering, University of Maryland, College Park, MD.
authors: Chao-Wei
authors: CW
authors: Chen
authors: School of Biomedical Engineering, Colorado State University, Fort Collins, CO.
authors: Kevin M
authors: KM
authors: Labus
authors: School of Biomedical Engineering, Colorado State University, Fort Collins, CO.|Department of Mechanical Engineering, Colorado State University, Fort Collins, CO.|Department of Clinical Sciences, Colorado State University, Fort Collins, CO.
authors: Christian M
authors: CM
authors: Puttlitz
authors: Fischell Department of Bioengineering, University of Maryland, College Park, MD.
authors: Yu
authors: Y
authors: Chen
authors: Fischell Department of Bioengineering, University of Maryland, College Park, MD.|Department of Orthopaedics, University of Maryland, Baltimore, MD.
authors: Adam H
authors: AH
authors: Hsieh
mesh_terms: D000818:Animals; D000070616:Annulus Fibrosus / Q000000981:diagnostic imaging* / Q000502:physiology*; D054459:Elasticity Imaging Techniques / Q000379:methods*; D033081:Shear Strength / Q000502:physiology*; D013314:Stress, Mechanical; D013552:Swine; D041623:Tomography, Optical Coherence / Q000379:methods*