What is healing of a long bone fracture?
Answer:
1. removeal of necrotic bone and debris by macrophages and osteoclasts
2. angiogenesis and fibroblast proliferation
3. callus formation: pluripotential mesenchymal cells from the soft tissue, periosteium and bone marrow proliferate and differentiate, composed of fibrous tissue, cartilage and bone, fusion of osteogenic layers on either side of the callus
4. remodeling phase: newly formed woven bone is gradually converted to lamellar bone, at about 8 weeks the callus is called a secondary or hard callus and it consists mainly of bone
5. stage of consolidation: endocondrial ossification of the cartilage continues, trabecular bone replaces cartilage, the new bone is continuously remodelled and eventually replaced by compact bone, dead bone removed before healing can be completed, eventually the oritinal line of the bone is restored (takes years)