Fractures and fracture healing
- Process
A broken bone heals through a clot, a cartilage and woven-bone callus, then remodelling. Movement, infection or poor blood flow can stop it.
What it is
Bone is one of the few tissues that heals by true regeneration rather than a scar. After a fracture, a haematoma forms and becomes the scaffold for inflammatory cells, growth factors and progenitor cells. Within about a week a soft callus of fibrous tissue, cartilage and woven bone bridges the gap; it is replaced by a bony callus of woven bone and finally remodelled into lamellar bone along the lines of stress. Fractures are described by whether the skin is broken, the number of fragments, displacement and cause (trauma, stress or pathologic).
Structure
- Days 1–3: haematoma with fibrin, platelets and neutrophils; dead bone at the fracture ends (empty osteocyte lacunae).
- End of the first week: soft callus of granulation tissue, fibroblasts, hyaline cartilage and spicules of woven bone that loosely bridge the ends.
- Weeks 2–3: cartilage undergoes endochondral ossification and the callus becomes woven bone; maximal girth.
- Months: remodelling by osteoclasts and osteoblasts replaces woven by lamellar bone and trims the excess callus.
- Pseudarthrosis: a cleft lined by synovium-like tissue between the ends, filled with fluid.
Step by step
- Torn vessels bleed and a haematoma fills the gap, sealing it and offering a fibrin mesh.
- Platelets and inflammatory cells release PDGF, TGF-β, FGF and BMPs, which recruit and activate progenitor cells.
- Periosteal and marrow progenitors form a soft callus of cartilage and woven bone within about a week.
- The cartilage is replaced through endochondral ossification and the ends are joined by woven bone (bony callus).
- Load-guided remodelling replaces woven with lamellar bone and restores the medullary canal over months.
- Motion, infection, poor blood flow or a missing gap filler disturb these steps and cause delayed union or nonunion.
Clinical notes
- Accurate reduction and immobilization speed healing; children heal faster and remodel angular deformities better than adults.
- Fractures of long bones and the pelvis can release marrow fat into the circulation: fat embolism syndrome within one to three days.
- Open fractures carry a high risk of osteomyelitis and need urgent debridement and antibiotics.
- Scaphoid and femoral neck fractures can lose their blood supply and progress to avascular necrosis.
Test yourself
Think of the answer, then tap the question to see it.
What tissue makes up the soft callus?
Granulation tissue with fibroblasts, hyaline cartilage and spicules of woven bone.
What is a pathologic fracture?
A fracture through bone already weakened by disease such as tumour, osteoporosis, osteomalacia or infection.
What causes a pseudarthrosis?
Persistent motion at a nonunited fracture, which creates a synovium-lined cleft like a false joint.
Why does bone heal without a scar?
Progenitor cells regenerate bone, first woven and then remodelled into lamellar bone.
Elsewhere in DurgiPedia
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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Fracture | MedlinePlus (MedlinePlus, US National Library of Medicine, 2025).
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Representative model, for educational purposes only.