Notes on Fracture Healing

Overview

• Fracture healing is a specialized type of wound healing.
• Composed of inflammation, repair, and remodeling.
• Restores injured bone.

Types of Bone Healing

1. Secondary Bone Healing

   • Occurs with some movement at the fracture site.
   • Involves a gradual transition of tissue types.
   • Natural healing in tubular bones.
   • Five overlapping phases:
     • Tissue destruction and hematoma formation
     • Inflammatory phase
     • Soft callus formation
     • Hard callus formation
     • Bone remodeling

2. Primary Bone Healing

   • Occurs when there is no movement (rigid internal fixation).
   • Bone heals directly.
   • Seen in impacted fracture in cancellous bones.
   • Two patterns observed:
     • Gap healing
     • Contact healing

Phases of Secondary Bone Healing

1. Tissue Destruction & Hematoma Formation

   • Vessels torn, hematoma forms.
   • Occurs around and within the fracture.

2. Inflammatory Phase

   • Acute inflammatory reaction within hours.
   • Influx of inflammatory cells.
   • Involves cytokines, transforming growth factor beta, and platelet-derived growth factor.

3. Soft Callus Formation

   • Hematoma is absorbed, new capillaries grow.
   • Mesenchymal stem cells proliferate and differentiate.
   • Osteoclasts clear dead bone.

4. Hard Callus Formation

   • Granulation tissue replaced with fibrous tissue and cartilage.
   • Formation of callus or splint.
   • Bone formation within soft callus.
   • Involves intramembranous and endochondral ossification.

5. Bone Remodeling

   • Immature woven bone becomes lamellar bone.
   • Osteoclasts and osteoblasts activity continues.
   • Consolidation occurs once the fracture is bridged by solid bone.
   • Remodeling process may take months/years.

Primary Bone Healing

• Gap Healing

  • New capillaries and osteoprogenitor cells fill the gap.
  • Formation of new bone, initially woven, then remodeled to lamellar.

• Contact Healing

  • Fracture surfaces in close contact and rigid.
  • Internal bridging without intermediate stages.

Additional Notes

• Bone remodeling unit starts acting by 3-4 weeks in primary healing.
• Involves creation of a new Haversian system.

Conclusion

• Discussion on the role of osteoclasts and the cutting cone will be provided in another video.
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This document captures the main points of a lecture on fracture healing, serving as a study aid for understanding the processes involved in bone repair and remodeling.