Stages of Bone Repair After a Fracture

Stage 1: Hematoma Formation

• Cause: Fracture results in torn blood vessels inside the bone.
• Effect: Local hemorrhage or bleeding occurs.
  • Bleeding is addressed through clotting, forming a hematoma.
  • Consequences include:
    • Swelling
    • Pain
    • Inflammation
    • Death of some bone cells due to lack of nutrition and inadequate blood supply.

Stage 2: Fibrocartilaginous Callus Formation

• Process:
  • Phagocytic cells move into the hematoma.
  • New blood vessels (capillaries) grow into the hematoma, reconnecting periosteum and endosteum.
  • Fibroblasts, chondroblasts, and osteoblasts invade the area.
• Functions of Cells:
  • Fibroblasts: Secrete collagen fibers to temporarily splint the bone fragments.
  • Chondroblasts: Secrete a cartilaginous matrix.
  • Osteogenic Cells: Give rise to osteoblasts, replacing cartilage with spongy bone.
• Outcome: Creation of a fibrocartilaginous callus, consisting of collagen, cartilage, and spongy bone.
  • This process mimics endochondral ossification.

Stage 3: Bony Callus Formation

• Transition:
  • Ossification of the previously deposited cartilage occurs.
  • Formation of new trabeculae from spongy bone within a week.
• Result:
  • Development of a more robust and harder structure compared to the fibrocartilaginous callus.
  • Within about two months, the fracture is replaced with spongy bone.

Stage 4: Bone Remodeling

• Objective: Re-establish normal bone structure.
  • Re-establish the medullary cavity.
  • Rebuild compact bone on the bone perimeter.
• Duration: Several months.
• Process:
  • Appositional growth based on stresses.
  • Removal of spongy bone from the medullary cavity.
• Completion: Bone repair concludes with remodeling.