Joints Degenerative - Pathology

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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

Cervical spinal stenosis

• Usually funnel-shaped
• Stenosis in dorso-ventral plane
• May occur at more than one site
• Predisposed in some breeds: Great Dane, Doberman, Basset Hound, Irish Wolfhound, Old English Sheepdog
• Clinical signs: cervical pain -> ataxia -> quadriplegia

Cervicospinal arthropathy

• = "Wobbler" in horses
• Usually presents in first two years of life
• Mainly in fast growing thouroughbreds
• Most common site is C3-C4, can occur anywhere
• Abnormal laxity between the vertebrae + cervical vertebral malformation may be evident
• Osteophyte formation at edges of synovial components of joint
• Some due to stenosis of neural canal later in life (1-4 years of age)
• Clinical signs:
  • Ataxia - hindlimbs more affected
• Presumed cause is rapid growth

Spondylosis

Spondylosis (Image sourced from Bristol Biomed Image Archive with permission)

• Often in bulls and dogs, occurs also in horses, cats and pigs
• Osteophyte formation on ventral aspect of vertebrae
  • Often around lumbar region
  • Adjacent to intervertebral spaces
  • Varies in size - small spurs -> 'bridges' between vertebrae
  • May extend over few vertebrae
• Pathogenesis:
  • Repeated abnormal movement between joints -> stress
  • -> Degeneration of annulus fibrosis
  • -> Osteophyte formation
• In dogs usually no symptoms
• In bulls may cause inability to mount
• In severe cases repeated damage may progress to recurrent posterior weakness and ataxia in conjuction with fractures of spondylitic and vertebral bone

Cranial cruciate ligament rupture

• Autoantibodies against collagens seen in the joint fluid – no relationship to the disease (ie: not an autoimmune disease) – can be seen in any joint disease

Steroid arthropathy

• From glucocorticoids injected into joint as antiinflammatories
• Injection sometimes causes rapid progression of degeneration
• Glucocortyicois suppress anabolic effect of chondrocytes -> reduction of cartilage matrix syhthesis -> proteoglycan depletion -> slower repair