Wound healing: Fracture healing

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Phases of bone healing

1. Reactive (Inflammatory) phase (0–7 days)

Vascular disruption leads to haematoma forms at fracture site.
Platelets release cytokines and growth factors.
Neutrophils and macrophages infiltrate, clear necrotic tissue, and release mediators.
Haematoma & fibrin scaffold supports migration of reparative cells.
Clinically: pain, swelling, and loss of function.

2. Reparative phase (1–6 weeks)

Fibroblasts and chondroblasts migrate in and form fibrocartilaginous soft callus.
Angiogenesis establishes granulation tissue and vascular supply.
Osteoblasts deposit woven bone which converts soft callus into hard callus.
Radiographic callus usually visible by 2–3 weeks.
Clinical/radiological union:
Children: often 3–6 weeks
Adults: typically 6–12 weeks (long bones longer, up to ~3 months).

3. Remodelling phase (months–years)

Woven bone replaced by lamellar bone.
Osteoclasts resorb excess callus; medullary canal restored.
Bone remodels along stress lines (Wolff’s law).
Can take 1–2 years (occasionally longer).
Final structure resembles original bone, with restoration of strength and shape.

Phases of fracture healing. Click on image to enlarge

Phase summary:
Haematoma → Soft callus → Hard callus → Remodelling

Condition	Definition	Causes	Clinical features	Management
Delayed Union	Slower-than-expected healing of a fracture, usually taking longer than the normal healing period but eventually uniting.	Poor blood supply Inadequate immobilization Infection Smoking Systemic diseases (e.g., diabetes).	Persistent pain, tenderness at the fracture site, minimal radiographic callus formation.	Optimize stability and blood supply; may involve bone stimulators or revision surgery in some cases.
Non-union	Failure of a fracture to unite after an extended period (typically 6–9 months), with no further progression toward healing. Types: Hypertrophic (adequate biology but insufficient stability); Atrophic (poor biology, often due to avascularity or severe soft tissue injury).	Infection Severe soft tissue damage Poor vascularity Metabolic disorders	Persistent mobility or deformity at the fracture site, chronic pain, radiographs show persistent fracture line with absent bridging callus.	Surgical fixation, bone grafting, or use of bone stimulators depending on type and cause.
Malunion	Healing of a fracture in an incorrect anatomical position.	Poor fracture reduction Inadequate immobilization Early weight-bearing.	Deformity, altered limb length or angulation, functional impairment.	Corrective osteotomy may be required if function or appearance is compromised.