Disc Protrusion

Intervertebral disc degeneration (Image sourced from Bristol Biomed Image Archive with permission)

• Occurs mainly in dogs
• Almost always dorsal protrusion due to eccentric position of nucleus pulposus
• Main sites are cervical and lumbar regions
  • Thoracic vertebrae have conjugal ligaments
• Degeneration precedes protrusion (two patterns):
  • Chondroid
    • In chondrodystrophic breeds
    • Concurrent calcification of degenerated nucleus pulposus
    • Progressive loosening and fragmentation of overlying annulus fibrosis fibres
      • Damaged by both compressive and rotational forces
    • Predisposing degeneration of the discs occurs by one year of age in most of the dogs
    • Protrusion usually occurs in males, 3-6 years of age
    • Sudden complete protrusion -> severe damage to spinal cord in the area
    • Widespread necrosis and haemorrhage
    • Extruded material is gritty, hemorrhagic or “cheesy”
  • Fibroid
    • In non-chondrodystrophic breeds, horses, pigs
    • Usually occurs later in life
    • Pathogenesis:
      • Progressive dehydration and collagenisation of nucleus pulposus
      • Fraying and fragmentation of lamellar annulus fibrosis fibres
      • -> Attempts to repair by fibrosis
      • -> Weak area in the annulus
      • -> Partial protrusion (rarely may calcify) of nucleus into spinal canal
        • May be dorsal or lateral
      • -> Pressure on spinal cord
      • -> Demyelination of white matter
      • -> Progressive weakness of structures innervated distally to the lesion
    • Disk material may enter blood vessels causing fibrocartilagenous embolism
      • May present without any disk symptoms

• Sudden protrusion can occur in any breed due to traumatic compression of spinal cord