Microstructural characterization of annulus fibrosus by ultrasonography: a feasibility study with an in vivo and in vitro approach

• Published in: Biomechanics and modeling in mechanobiology 2019-12, Vol.18 (6), p.1979-1986
• Main Authors: Langlais, Tristan, Desprairies, Pierre, Pietton, Raphael, Rohan, Pierre-Yves, Dubousset, Jean, Meakin, Judith R., Winlove, Peter C., Vialle, Raphael, Skalli, Wafa, Vergari, Claudio
• Format: Article
• Language: English
• Subjects: Adolescent; Adolescents; Animals; Annuli; Annulus Fibrosus - diagnostic imaging; Bioengineering; Biological and Medical Physics; Biomechanics; Biomedical Engineering and Bioengineering; Biophysics; Body mass index; Body size; Cattle; Child; Degeneration; Engineering; Engineering Sciences; Feasibility Studies; Female; Humans; Image acquisition; Imaging; In vivo methods and tests; Intervertebral discs; Lamellae; Lamellar structure; Life Sciences; Light microscopy; Lumbar Vertebrae - diagnostic imaging; Magnetic resonance; Male; Mechanical properties; Mechanics; Microstructure; Multimodal Imaging; Optical microscopy; Original Paper; Reliability analysis; Scoliosis; Space life sciences; Spinal cord; Spine; Spine (lumbar); Theoretical and Applied Mechanics; Thickness measurement; Ultrasonic imaging; Ultrasonography; Ultrasound
• ISSN: 1617-7959; 1617-7940
• DOI: 10.1007/s10237-019-01189-3

The main function of the intervertebral disc is biomechanical function, since it must resist repetitive high loadings, while giving the spine its flexibility and protecting the spinal cord from over-straining. It partially owes its mechanical characteristics to the lamellar architecture of its outer layer, the annulus fibrosus. Today, no non-invasive means exist to characterize annulus lamellar structure in vivo. The aim of this work was to test the feasibility of imaging annulus fibrosus microstructure in vivo with ultrasonography. Twenty-nine healthy adolescents were included. Ultrasonographies of L3–L4 disc were acquired with a frontal approach. Annulus fibrosus was segmented in the images to measure the thickness of the lamellae. To validate lamellar appearance in ultrasonographies, multimodality images of two cow tail discs were compared: ultrasonography, magnetic resonance and optical microscopy. In vivo average lamellar thickness was 229.7 ± 91.5 μm, and it correlated with patient body mass index and age. Lamellar appearance in the three imaging modalities in vitro was consistent. Lamellar measurement uncertainty was 7%, with good agreement between two operators. Feasibility of ultrasonography for the analysis of lumbar annulus fibrosus structure was confirmed. Further work should aim at validating measurement reliability, and to assess the relevance of the method to characterize annulus alterations, for instance in disc degeneration or scoliosis.