Muscle Ischaemia

Firstly segmental necrosis
-> death of satellite cells
- Causes regeneration but myoblast precursors have to be recruited from viable fibres
-> death of all cells
Mostly healed by fibrosis and scar formation
May attempt regeneration by budding

Main causes:

Vascular occlusion
- Infarction from embolism is rare due to collateral circulation
- Extension of infarcts depends on size of vessels occluded
  - Small capillaries -> segmental necrosis
  - Large arteries -> whole muscle areas, including sattelite cells, are killed
- Healed by fibrosis
- May be due to:
  - Blockage of iliac arteries by aortic-iliac thrombosis in horses
  - Blockage of aortic bifurcation in cats
  - Dirofilaria immitis arteritis in dogs
  - Vasculitis due to bluetongue virus in sheep
  - Equine purpura haemorrhagica
    - Non-contagious, sporadic
    - Grossly:
      - Subcutaneous oedema
      - Scattered haemorrhagic foci throughout skin and muscles
      - Vasculitis -> infarcts of muscles
    - May cause myoglobinuria if extensive
    - Possibly immune mediated
    - In horses post streptococal infection, especially strangles
External pressure
- During prolonged recumbency, e.g. anaesthesia, inability to rise, or due to too tightly fitting bandages or casts
- Post anaesthesia myopathy especially in horses
  - Dorsal recumbancy -> gluteals and longissimus ischaemia
  - Lateral recumbancy -> triceps brachii, pectoralis, deltoideus and brachiocephalicus ischaemia
- Caused by pressure on muscle > perfusion pressure of capillaries
- Downer cows - vetral recumbency -> ischaemia of pectoral muscles and muscles of limbs tucked under the animal
- Pregnant ewes with twins or triplets -> internal abdominal oblique muscle ischaemic necrosis -> potential rupture
Muscle swelling where it cannot expand
- E.g. supracoracoid muscle infarction in some breeds of turkeys after flapping their wings
  - Surrounded by inelastic fascial sheath and bone