Intervertebral Disc

• Intervertebral disc degeneration - biomechanical changes:

  • Decrease in proteoglycans - less proteoglycan synthesis in nucleus pulposus as we get older, PG go from 65% of dry weight of nucleus pulposus to 30% by 60 yrs
  • Collagen changes from type 2 to 1 - less resilient, less elastic
  • Decrease in water content - caused by collagen change and decrease in Proteoglycans
  • Decrease in elastic fibres - caused by collagen change and decrease in Proteoglycans
• Intervertebral disc degeneration - biomechanical changes pt 2:

  • in annulus pulposus theres an increase in collagen conc, but a decrease in conc of elastic fibres from 13% to 8% by 60 yrs
  • also increase in type 1 collagen in outer layers of lamellae - less elastic
  • so overall discs become drier with age
  • increase in collagen and decrease in elastin makes them more fibrous -> stiffer and less resilient
  • therefore become less mobile with time
• Intervertebral disc degeneration - structural changes:

  • the biomechanical changes of the disc getting drier, stiffer and less resilient contribute to the progressive structure failure
  • as age increases, the end plate becomes thinner
  • cell death occurs at the superficial layers of the cartilage
  • the vascular channels in the subchondral bone are gradually closed off -> subchondral bone is no longer fit / theres no good nutrition -> decrease in strength of the end plates
  • compramised structural integrity = decreased strength / resilience and (impaired) ability to do its job
• Intervertebral Disc Degeneration - (Adams et al., 2006):

  • “disc degeneration is an aberrant cell-mediated response to progressive structural failure”
  • split into 2 phases:
  • biomechanical changes leading to
  • structural changes
• Intervertebral disc

  • Consists of the nucleus pulposus, annulus fibrosus, and vertebral end plates

  A) Intervertebral Disc

  
• Structure of the Intervertebral Disc - within the intervertebral disc - Nucleus pulposus:

  • semi fluid mass of mucoid material

  A) Nucleus Pulposus

  
• Structure of the Intervertebral Disc - within the intervertebral disc - Annulus fibrosus:

  • made from collagen fibres in a highly organised pattern
  • surrounds nucleus pulposus
  • characterised by lamellae which are thicker towards the centre, anteriorly and laterally, but thinner posteriorly where they're mostly packed
  • rich with proteoglycan gel so helps provide torsional strength to the disk, maintains integrity of the disc and intradiscal pressure

  A) Annulus fibrosus

  
• Structure of the Intervertebral Disc - within the intervertebral disc - Vertebral end plate:

  • 2 layers of cartilage which cover the top and bottom of the disc, cover all of nucleus pulposus and some of annulus fibrosus until the periphery
  • Consists of both hyaline cartilage (towards the end of vertebral body, mostly evident in younger discs) and fibrocartilage (occurs towards the nucleus pulposus, so more towards the middle and more evident in older discs)

  A) Vertebral end plate