Fracture Healing

Fracture Healing - Bone's Break & Mend

• Healing Types:
  • Primary (Direct): Rigid fixation, no callus. Gap < 200 µm.
  • Secondary (Indirect): Commonest, involves callus, tolerates some motion.
• Secondary Healing Stages:
  • 1. Hematoma/Inflammation (0-7 days): Clot, inflammatory cells, growth factors.
  • 2. Soft Callus (1-3 wks): Granulation tissue, fibrocartilage (fibroblasts/chondrocytes). Initial stability.
  • 3. Hard Callus (3-12 wks): Woven bone via endochondral ossification. Osteoblasts active.
  • 4. Remodeling (months-yrs): Woven bone → lamellar bone. Medullary canal restored. Wolff's Law.

⭐ Wolff's Law: Bone remodels along lines of mechanical stress, adapting structure to demands.

Fracture Healing Stages - The Repair Crew

Fracture healing is a dynamic, multi-stage process restoring bone integrity. Most common is indirect (secondary) healing with callus formation.

• Stage 1: Haematoma & Inflammation (0-7 days)

  • Blood clot (haematoma) forms, fibrin mesh.
  • Influx of neutrophils, macrophages.
  • Release of cytokines & growth factors (PDGF, TGF-β).
  • Granulation tissue begins.

• Stage 2: Soft Callus Formation (1-3 weeks)

  • Fibroblasts & chondroblasts proliferate.
  • Haematoma replaced by fibrocartilaginous (soft) callus.
  • Provides initial stability; not for weight-bearing.

  ⭐ Soft callus is typically visible on X-ray by 2-3 weeks.

• Stage 3: Hard Callus Formation (3-12 weeks)

  • Endochondral ossification: soft callus → woven bone by osteoblasts.
  • Mineralization increases callus strength.
  • Clinical union: no pain/movement at fracture site.

• Stage 4: Remodelling (Months to Years)

  • Woven bone gradually replaced by lamellar bone.
  • Medullary canal restored.
  • Bone reshaped by osteoclastic & osteoblastic activity (Wolff's Law).
  • Radiological union: fracture line disappears.

Fracture Healing Factors - Boosters & Blockers

• Boosters (Promote Healing):
  • Systemic Factors:
    • Young age, good health
    • Nutrition (Protein, Vit C, D, $Ca^{2+}$)
    • Hormones (GH, Thyroid, Calcitonin)
  • Local Factors:
    • Good vascularity
    • Immobilization & stability
    • Growth factors (BMPs, TGF-β)
    • Minimal tissue damage, no infection
• Blockers (Impair Healing):
  • Systemic Factors:
    • Old age, malnutrition, smoking
    • Corticosteroids, NSAIDs (esp. early phase)
    • DM, severe anemia, hypoxia
    • Cytotoxic drugs, Immunosuppression
  • Local Factors:
    • Infection
    • Poor vascularity (AVN risk)
    • Instability / movement, large gap
    • Soft tissue interposition, severe comminution
    • Bone loss, malignancy

⭐ Infection is the most common cause of delayed union and non-union.

Fracture Healing Complications - When Mends Go Awry

• Malunion: Heals in a non-anatomical position.
  • Angular or rotational deformity.
• Delayed Union: Healing takes longer than expected (typically >3-6 months).
  • Causes: Poor blood supply, infection, inadequate immobilization.
• Nonunion: Failure of fracture to heal by >6-9 months.
  • Types: Hypertrophic (elephant foot), Atrophic (pencil point), Oligotrophic.
  • Requires intervention (e.g., bone graft, internal fixation).
• Avascular Necrosis (AVN): Bone death due to ↓ blood supply.
  • Common sites: Femoral head, scaphoid, talus.

• Compartment Syndrome: ↑ pressure within a fascial compartment.
  • Leads to muscle and nerve ischemia.
  • ⚠️ Surgical emergency: Fasciotomy.
• Infection (Osteomyelitis): Bacterial contamination.
• Pseudoarthrosis: False joint formation at nonunion site.
• Complex Regional Pain Syndrome (CRPS): Chronic pain, swelling, autonomic dysfunction.

⭐ Hypertrophic nonunion often indicates good vascularity but poor stability, whereas atrophic nonunion suggests poor vascularity and biology at the fracture site.

• Fat Embolism Syndrome: Fat globules enter circulation, common in long bone fractures (femur, tibia).
  • Triad: Respiratory distress, neurological symptoms, petechial rash (📌 Fat Embolism Syndrome = Fever, Encephalopathy, Skin rash).

High‑Yield Points - ⚡ Biggest Takeaways

• Fracture healing stages: Hematoma, inflammation, soft callus (fibrocartilage), hard callus (woven bone), remodeling (lamellar bone).
• Primary healing: Occurs with rigid fixation, no external callus, direct Haversian remodeling.
• Secondary healing: Most common, involves granulation tissue, callus formation, endochondral ossification.
• Key cells: Platelets, macrophages, fibroblasts, chondroblasts, osteoblasts, osteoclasts.
• Critical growth factors: BMPs (Bone Morphogenetic Proteins), TGF-β, PDGF, FGF.
• Factors impairing healing: Instability, poor vascularity, infection, NSAIDs, smoking, diabetes.
• Complications: Delayed union, non-union (hypertrophic/atrophic), malunion, pseudoarthrosis.