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Fracture Healing

Fracture healing is the biological process by which a broken bone restores its continuity, strength, and function. It occurs through either primary (direct) healing, seen with absolute stability, or secondary (indirect) healing, which progresses through inflammation, soft callus formation, hard callus formation, and remodelling. Healing depends on adequate blood supply, mechanical stability, and the patient’s biological environment.

Fracture healing is a highly coordinated biological process that restores the structural integrity and mechanical strength of bone after injury. Unlike most tissues, bone can heal by regeneration with formation of new bone rather than scar tissue. Fractures heal by two main mechanisms: primary bone healing and secondary bone healing. Primary or direct healing occurs when there is absolute stability and minimal fracture gap, typically after rigid internal fixation. In this process, osteoclasts and osteoblasts remodel directly across the fracture line with little or no visible callus formation. Secondary or indirect fracture healing is more common and occurs when there is relative stability with controlled micromotion. It progresses through overlapping stages. The initial inflammatory phase involves hematoma formation and recruitment of inflammatory and reparative cells. This is followed by formation of a soft callus, in which fibrous tissue and cartilage bridge the fracture. The soft callus is then mineralized to form a hard bony callus, mainly through endochondral and intramembranous ossification. Finally, during the remodelling phase, woven bone is gradually replaced by organized lamellar bone and the bone adapts to mechanical loading according to Wolff’s law. Fracture healing is influenced by several factors, including vascularity, fracture pattern, degree of soft-tissue injury, stability, infection, smoking, nutrition, age, medications, and systemic disease. Excessive motion, poor blood supply, infection, or a large fracture gap may lead to delayed union or non-union. The aim of fracture management is therefore to provide an appropriate mechanical and biological environment that allows healing while maintaining alignment and restoring limb function.

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