Bones Degenerative - Pathology

()Map MUSCULOSKELETAL SYSTEM (Map) BONES

Bones and Cartilage - Metabolic diseases

Bones and Cartilage - Fractures

Osteoporosis (Atrophy)

• Lesion, not a disease
• Reduction in bone mass due to reduced osteoid (bone atrophy)
• Bone resorption exceeds formation -> pathological loss of bone
• Resorbed from:
  • Trabeculae, preserving the weight bearing ones until last
  • Endosteal surface of cortical bone
  • Along vascular channels
• Longitudinal section
  • Fewer thin trabeculae
  • Enlarged medulla
  • Thin, porous cortex
• Bone which remains is normally mineralised
• Can be localised or generalised*Caused by:
  • Starvation - in farm animals due to protein and energy deficiency
  • Nutritional deficiency (calcium) and hypocalcaemia -> bone resorption
  • Senility
    • Physiological loss of skeletal mass with age
    • May be excessive in some individuals
    • Histologically - dead osteocytes and empty lacunea
  • Physical inactivity (disuse) - muscular inactivity and reduced weight bearing, e.g. during limb casting
  • Glucocorticoids
  • Intestinal parasitism - in ruminants, malabsorption due to severe infestation
  • Copper deficiency - in lambs, calves, foals, pigs and dogs -> brittle bones
• May be reversed in young growing animals

Osteosis

• Also called Aseptic necrosis or Ischaemic necrosis
• Degeneration and necrosis of osseous tissue
• Due to bone marrow pressure and ischaemia resulting from
  • Fractures
  • Excessive heat e.g. horn disbudding
  • Neoplasia (osteosarcoma and lymphosarcoma)
• Grossly:
  • Necrotic bone difficult to recognise
  • Sometimes, periosteum becomes dry, dull and detaches easily
  • On longitudinal section
    • Yellow-white necrotic bone
    • Scattered cancellous and endosteal bone
• Histologically:
  • Empty lacunae or contain dead osteocytes
  • Matrix remains mineralised
• Necrotic bone is slowly resorbed, sequstered or covered by new woven bone
• Persists
• May not be detected radiographically
• Associated with Calve-Legg Perthe's disease

Bone cysts

Bone cysts (Image sourced from Bristol Biomed Image Archive with permission)

• May be seen radiographically
• Must be distinguished from neoplasia
• Expansile lytic masses
• Do not appear aggressive
• Subchondral cysts
  • Common in horses and pigs
  • Usually manifestations of osteochondrosis and DJD
• Simple cysts
  • May contain clear colourless fluid, or serosanguinous
  • Wall of dense fibrous tissue, woven or lamellar bone
• Aneurysmal bone cysts
  • Expansie lesions
  • Arise from disturbance of vascular tissue of bone marrow
  • Grossly:
    • Appear as blood filled sponge
    • Spaces separated by fibrous trabeculae
  • Histologically:
    • Proliferation of undifferentiated mesenchymal cell with multinucleated osteoclast-like cells
    • Haemorrhage and haemosiderosis
• Radiography is essential to help differentiate with cavity of a neoplasm

Calcium hydroxylapatite deposition disease

• Gt Dane puppies with paraplegia
• Calcium phosphate depositon has been reported in multiple diarthrodial joints of the axial and appendicular skeleton
• More about Calcium hydroxylapatite deposition disease

Physeal dysplasia with slipped capital femoral epiphysis

• Slipped capital femoral epiphysis seen in dogs, foals and calves
• Associated with severe trauma
• Pigs – manifestation of osteochondrosis with only minimal trauma required
• Most common type of physeal fracture in small animals and the proximal femur is the most common site
• In horses, physeal dysplasia is synonymus with physitis
• More about Physeal dysplasia