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Intervertebral disc..tesf.pptx
- 2. Anatomy • Function • allows spinal motion and provides stability • links adjacent vertebral bodies together • responsible for 25% of spinal column height • •
- 3. Composition
- 4. 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 • •
- 5. 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 and survive in hypoxic conditions • •
- 6. 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 • •
- 8. 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 • •
- 9. Fixation • attached to vertebral bodies by hyaline cartilage • •
- 10. 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
- 11. 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 • •
- 12. Pathoanatomy • herniated disks are associated with a spontaneous increase in the production of • osteoprotegrin (OPG) • interleukin-1 beta receptor activator of nuclear factor-kB ligand (RANKL) parathyroid hormone (PTH)
- 13. Ctnd... • Disc aging leads to an overall loss of water content and conversion to fibrocartilage. • Specifically there is a decrease in - nutritional transport • - water content • - absolute number of viable cells • - proteoglycans • - pH • increase in - an increase keratin sulfate to chondroitin sulfate ratio • - lactate • - degradative enzyme activity • - density of fibroblast-like cells ( fibroblast-like cells reside in the annulus fibrosus only) • no change in--- absolute quantity of collagen • • •