Lumbar Intervertebral Disc

  • Function

    • allows spinal motion and provides stability

    • links adjacent vertebral bodies together

    • responsible for 25% of spinal column height

  • Composition 

    • annulus fibrosus

      • outer structure that encases the nucleus pulposus

      • composed of type I collagen that is obliquely oriented, water, and proteoglycans

      • characterized by high tensile strength and its ability to prevent intervertebral distraction

      • remains flexible enough to allow for motion

      • high collagen / low proteoglycan ratio (low % dry weight of proteoglycans) 

      • fibroblast-like cells

        • responsible for producing type I collagen and proteoglycans

    • nucleus pulposus

      • central portion of the intervertebral disc that is surrounded by the annulus fibrosis

      • composed of type II collagen, water, and proteoglycans

        • approximately 88% water

      • hydrophilic matrix is responsible for height of the intervertebral disc

      • characterized by compressibility

        • a hydrated gel due to high polysaccharide content and high water content (88%)

          • proteoglycans interact with water and resist compression

            • Aggrecan is a proteoglycan primarily responsible for maintaining water content of the disc 

        • viscoelastic matrix distributes the forces smoothly to the annulus and the end plates

      • low collagen / high proteoglycan ratio (high % dry weight of proteoglycans)  

      • chondrocyte-like cells

        • responsible for producing type II collagen and proteoglycans

        • survive in hypoxic conditions

  • Blood Supply  

    • the disk is avascular with capillaries terminating at the end plates

    • nutrition reaches nucleus pulposus through diffusion through pores in the endplates 

      • annulus is not porous enough to allow diffusion 

  • Innervation

    • the dorsal root ganglion gives rise to the sinuvertebral nerve which innervates the superficial fibers of annulus

      • no nerve fibers extend beyond the superficial fibers

    • neuropeptides thought to participate in sensory transmission include

      • substance P

      • calcitonin

      • VIP

      • CPON

  • Fixation

    • attached to vertebral bodies by hyaline cartilage

Disc Biomechanics

  • Disc

    • viscoelastic characteristics

      • demonstrates creep which allows for deformity over time

      • demonstrates hysteresis which allows for energy absorption with repetitive axial compression

        • this property decreases with time

  • Stresses

    • annulus fibrosus

      • highest tensile stresses

    • nucleus pulposus

      • highest compressive stress

    • intradiscal pressure is position dependent

      • pressure is lowest when lying supine

      • pressure is intermediate when standing

      • pressure is highest when sitting and flexed forward with weights in the hands

      • when carrying weight, the closer the object is to the body the lower the pressure

  • Stability

    • following subtotal discectomy, extension is most stable loading mode

 (808)-261-8181
Fax (808) 261-7770
Chiropractor Kailua, HI
  228 Kuulei Rd.
Kailua, HI 96734
 

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