Q.Explain the phases of healing of bones in fracture.

A broken bone heals through an orderly four-stage sequence -- clotting, soft callus, hard callus, and remodelling -- that together restore both continuity and strength to the bone.

1. Haematoma (blood clot) formation (first few hours-days)

• The fracture tears blood vessels in the bone and periosteum, causing bleeding at the site.
• The blood clots to form a haematoma, which seals off the broken ends and cuts off blood supply to the immediately adjacent bone cells (causing localised cell death).
• Inflammatory cells (neutrophils, macrophages) and fibroblasts migrate in, and new capillaries begin to sprout into the clot -- this is the inflammatory phase.

2. Fibrocartilaginous (soft) callus formation (about 1-3 weeks)

• Fibroblasts produce collagen fibres and chondroblasts produce cartilage within the haematoma, forming a soft, spongy mass called the procallus that bridges the broken ends.
• This soft callus is not rigid but is strong enough to loosely splint the fracture.

3. Bony (hard) callus formation (about 4-6 weeks)

• Osteoblasts migrate into the soft callus and progressively replace the fibrocartilage with spongy (woven/immature) bone through endochondral ossification.
• This converts the soft callus into a hard, calcified callus firmly uniting the fracture.

4. Bone remodelling (months to over a year) …