- Metaplasia of muscle to bone
- Localised
- Only in single muscle or a single group of muscles
- May be associated with trauma
- Seen in horses and dogs
- Histologically:
- Central zone - proliferating undifferentiated cells and fibroblasts
- Middle zone - osteoblasts depositing osteoid and bone
- Outer zone - trabecular bone remodelled by osteoclasts
- Progressive (fibrodysplasia ossificans progressiva)
- In connective tissue associated with skeletal muscle
- Secondary involvement of muscle tissue
- In pigs and cats
- Histologically:
- Bundles of dense fibrous connective tissue
- May contain accumulations of cartilage, bone or calcium
- Hyperplastic connective tissue -> compression of adjacent skeletal muscle -> atrophy