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Fracture Healing: Foundational Concepts
Fracture healing is a coordinated biological and mechanical process that restores continuity and, ideally, the original strength and function of bone. It requires viable bone ends, adequate blood supply, appropriate mechanical stability, and a biologically favourable local and systemic environment. Healing occurs through overlapping phases rather than sharply separated stages. The relative contribution of inflammation, repair and remodelling varies with the type of fracture, soft-tissue injury, stability of fixation and vascularity.
Two broad patterns of healing are recognised:
- Secondary or indirect fracture healing: the common pattern in untreated fractures and fractures managed with relative stability. It proceeds through haematoma formation, inflammation, soft callus, hard callus and remodelling. Some interfragmentary movement is tolerated and callus formation is prominent.
- Primary or direct fracture healing: occurs under conditions of anatomical reduction and very rigid fixation, with minimal interfragmentary strain. Healing proceeds by direct osteonal and cutting-cone activity across the fracture line, with little or no external callus.
Comparison of Primary and Secondary Healing
| Feature | Primary healing | Secondary healing |
|---|---|---|
| Mechanical environment | Absolute stability; negligible interfragmentary movement | Relative stability; controlled movement permitted |
| Reduction and fixation | Usually anatomical reduction with compression plating or equivalent fixation | Bridging, splintage, intramedullary fixation or external fixation |