Joints Degenerative - Pathology

Luxations and subluxations

Patellar

• In stifle joints of dogs and horses
• Possibly inherited
• Small dog breeds:
  • Medial luxation
  • Due to underdevelopment of medial femoral condyle
• Large dog breeds and horses:
  • Lateral luxation

Atlantoaxial

• In dogs, calves, horses and goats
• Miniature dog breeds:
  • Failure of fusion of odontoid process to rest of axis
• Calves:
  • Aplasia or hypoplasia of odontoid process

Temporomandibular

• In dogs, particularly Basset Hounds, Irish Setters
• Normal movement of mandibular coronoid process is interfered with by zygomatic arch
• Happens on one side -> open jaw locking

Calve Legg-Perthe's disease

• Almost exlusively in small dogs, particularly terriers and poodles
• Clinical signs appear at age of 4-11 months
• Grossly:
  • Aseptic ischaemic necrosis in central parts of femoral head
    • Possibly due to occlusion of blood vessels
  • Fragmentation of trabecular bone
  • Collapse of femoral head
  • Revascularisation of femoral head
  • Formation of new bone and osteophyte formation around femoral head and acetabular rim prior to old bone reabsorption
  • -> severe degenerative arthropathy

Degenerative arthropathy

• In older dogs (8+ years)
• Occurs bilaterally
• In shoulders
• ?Due to gradual atrophy of muscles with age -> joint laxity

Traumatic injuries

• Sudden
• Varying severity
• Acute injuries:
  • Sprains
    • Minor - resolved without any consequences
    • More severe may result in persistent capsular and ligament laxity -> degenerative arthrosis -> impaired function
  • Subluxations
  • Luxations
  • Intra-articular fractures
    • Fracture healing may cause discontinuity of the articular surfaces
  • Puncture wounds to foot may allow infection to travel to joints, bursae and tendon sheaths
  • Haemorrhage into joint
    • May occur in animals with clotting defects without special trauma
      • Usually polyaricular
      • Recurrent
      • May cause pitting of articular surfaces -> degenerative arthrosis

Nutritional diseases

Hypervitaminosis A

• See metabolic diseases of bones
• May cause spondylosis of cervical vertebrae
• Mainly on dorsolateral surface
• Also in elbow and shoulder joints -> fixation of joint
• May resolve with changes of diet

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