Bone Healing Stages and Types

Overview

This lecture explains the stages of bone healing after a fracture and distinguishes between primary and secondary bone healing processes.

Bone fracture is called a fracture and healing occurs in several stages.
The first stage is hematoma formation, where bleeding creates a fibrin blood clot at the fracture site.
This is followed by the inflammation stage, where macrophages and mesenchymal stem cells migrate to form granulation tissue and release growth factors.
The soft callus stage usually occurs within two weeks, forming a connective tissue bridge between broken bone ends.
Amount of callus formed correlates with the type of immobilization; flexible fixation increases callus formation.
The hard callus stage involves conversion of cartilage (type 2 collagen) to bone (type 1 collagen).
The final stage is remodeling, where woven bone is replaced by strong lamellar bone, restoring normal structure.

Secondary bone healing involves cartilage formation (endochondral ossification) and occurs with less rigid fixation (e.g., casts, rods).
Primary bone healing involves direct bone formation (intramembranous healing or cutting cone remodeling) and requires absolute stability (e.g., plates).
Secondary healing produces abundant callus; primary healing produces little or no callus.
Type 1 collagen is found in bone, while type 2 collagen is found in cartilage.

Cox-2 inhibitors and NSAIDs can inhibit important factors necessary for bone healing.
Wolf’s law states that bone remodeling is influenced by physical stress.

Hematoma — a localized collection of blood outside blood vessels, forming the initial blood clot after fracture.
Callus — new tissue that bridges and stabilizes the fracture.
Endochondral Ossification — bone formation through a cartilage intermediate.
Intramembranous Healing — direct bone formation without cartilage.
Type 1 Collagen — main collagen in bone tissue.
Type 2 Collagen — main collagen in cartilage.

Review the stages of bone healing in order: hematoma, inflammation, soft callus, hard callus, remodeling.
Know the differences between primary and secondary bone healing for exams.