Bone Healing Process

Overview

• Fracture: A break in the bone.
• Healing involves several stages: hematoma formation, inflammation, soft callus formation, hard callus formation, and remodeling.

Stages of Bone Healing

1. Hematoma Formation

• Occurs immediately after fracture.
• Bleeding at fracture site forms a fibrin blood clot.

2. Inflammation Stage

• Follows hematoma formation.
• Involved cells: Macrophages and mesenchymal stem cells.
• Process:
  • Stem cells migrate to fracture site.
  • Formation of granulation tissue.
  • Release of growth factors aiding in healing.
• Influence:
  • COX-2 inhibitors and non-steroidal drugs can depress COX-2, crucial for osteoblast differentiation.

3. Soft Callus Stage

• Timeline: Occurs within two weeks.
• Correlation: Amount of callus depends on immobilization.
  • Stiffer immobilization: Less callus.
  • Flexible fixation: Results in endochondral ossification and abundant callus.

4. Hard Callus Stage

• Occurs after soft callus formation.
• Process: Collagen changes from type 2 to type 1.

5. Remodeling Stage

• Timeline: Begins early, continues for years after fracture healing.
• Process: Woven bone replaced by stronger laminar bone.
• Influence: Wolf's Law (bone affected by stress).

Types of Bone Healing

Secondary Bone Healing

• Process: Through cartilage formation.
• Stability: Lack of stability aids cartilage formation, leading to endochondral ossification.
• Application: Occurs with non-rigid fixation (e.g., cast, intramedullary rod).
• Collagen Type: Type 2 collagen.

Primary Bone Healing

• Process: Involves absolute stability.
• Methods: Haversian remodeling, cutting cone remodeling, or intramembranous healing.
• Application: Occurs with rigid fixation (e.g., plates).
• Collagen Type: Type 1 collagen; bone forms before cartilage.

Conclusion

• Order of Stages: Hematoma → Inflammation → Soft Callus → Hard Callus → Remodeling.
• The healing process is complex and involves changes at cellular and structural levels to ensure proper bone repair.