Bones Degenerative - Pathology

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

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 (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

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

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

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