Fracture Healing: Phases, Biology, Factors, Complications and Emergency Care

Fracture healing is a coordinated repair response that restores bone continuity and, when possible, the original strength and shape. It requires a viable blood supply, inflammatory signalling, mesenchymal stem cells, cartilage and bone formation, mechanical stability and later remodelling. Emergency clinicians influence the biology from the first minutes by controlling haemorrhage, protecting soft tissue, reducing gross contamination, restoring alignment and preventing avoidable ischaemia.

Learning outcomes

After studying this page, the learner should be able to define fracture healing, describe the cells and signals involved, distinguish primary from secondary healing, outline the phases and expected clinical/radiographic findings, identify factors that accelerate or delay union, recognise delayed union, non-union and malunion, and apply emergency principles to open and complicated fractures.

1. What is a fracture and what does healing mean?

A fracture is a disruption of the structural continuity of bone. It may be traumatic, stress-related, pathological or iatrogenic, and it may be closed or open. Healing means restoration of a load-bearing bridge across the fracture, with progressive recovery of stiffness, strength and function. Radiographic bridging is important but is not identical to biological union: a patient may have pain-free clinical union before complete remodelling, or an apparently bridged film with persistent weakness in a high-demand bone.

Bone heals differently from skin. It can regenerate with tissue that is structurally similar to the original bone, but only if the local cells, blood vessels, matrix and mechanical environment remain suitable. A fracture also injures periosteum, endosteum, marrow, muscle and vessels, so the repair response is a tissue-level process rather than simply “new bone filling a crack.”

2. The local biology of a fracture

2.1 Blood supply

• Periosteal vessels supply the outer cortex and are especially important in children and in callus formation.
• Nutrient and endosteal vessels supply marrow and the inner cortex; disruption can produce cortical necrosis and delayed union.
• Soft-tissue stripping, high-energy injury, repeated surgery, infection and smoking can reduce perfusion even when the main artery remains patent.

2.2 Cells

Cell	Main role	Clinical relevance
Platelets and inflammatory cells	Initiate clotting and release cytokines and growth factors	Early inflammation is necessary; uncontrolled infection causes destructive inflammation
Mesenchymal stem/progenitor cells	Differentiate toward fibroblasts, chondrocytes and osteoblasts	Provide the cellular pool for soft and hard callus
Fibroblasts	Produce collagen-rich fibrous tissue	Form the early flexible bridge
Chondrocytes	Produce cartilage in low-oxygen, relatively unstable areas	Build the soft callus for endochondral ossification
Osteoblasts	Synthesise osteoid and mineralise new bone	Produce woven bone directly or after cartilage replacement
Osteoclasts	Resorb damaged or excess bone	Shape the callus and participate in remodelling
Endothelial cells/pericytes	Generate new microvasculature	Angiogenesis is essential for oxygen delivery and osteogenesis

2.3 Signalling pathways

Platelet-derived growth factor, transforming growth factor-beta, fibroblast growth factors, vascular endothelial growth factor and bone morphogenetic proteins (BMPs) coordinate inflammation, angiogenesis and osteogenic differentiation. Wnt signalling supports osteoblast activity and bone formation. Hypoxia-inducible pathways help recruit vessels, but prolonged severe hypoxia, acidosis or infection shifts the environment toward necrosis and fibrous non-union. These pathways interact with parathyroid hormone, vitamin D, calcium-phosphate metabolism and local mechanical signals.

3. Phases of secondary (indirect) fracture healing

These phases overlap; they are a useful framework rather than rigid calendar boxes. The duration varies with bone, fracture pattern, age, soft-tissue injury and fixation.

Phase 1: Haematoma and inflammation (hours to approximately 1 week)

• Ruptured vessels produce a fracture haematoma and fibrin scaffold. The initial clot is not merely debris; it concentrates cells and growth factors.
• Platelets, neutrophils and macrophages remove damaged material and release mediators that recruit progenitor cells and stimulate angiogenesis.
• Necrotic bone at the fracture ends is gradually demarcated. Excessive tissue destruction, an open wound or a large devascularised fragment enlarges this zone and worsens prognosis.
• Clinically, pain, swelling, bruising and loss of function are prominent. Fever or severe systemic toxicity is not a normal consequence and should prompt assessment for infection or another injury.

Phase 2: Granulation tissue and soft callus (approximately 1–3 weeks)

Fibroblasts and chondrocytes bridge the gap with collagen and cartilage. The soft callus stabilises the fracture enough for later bone formation but has limited load-bearing strength. New capillaries grow into the repair tissue. Excessive motion maintains fibrous tissue and prevents progression; moderate controlled strain can stimulate callus in secondary healing.

Phase 3: Hard callus and woven bone (approximately 3–8 weeks, often longer)

As vascularity improves, cartilage is replaced by woven bone through endochondral ossification. Osteoblasts also lay down woven bone directly in well-oxygenated areas. The external callus becomes mineralised and bridges the fracture; pain and abnormal movement diminish. Radiographs show increasing callus and fading fracture lines, but the woven bone is not yet organised like mature lamellar bone.

Phase 4: Remodelling (months to years)

Osteoclasts remove excess callus and osteoblasts replace it with stronger lamellar bone. The medullary canal is re-established and trabeculae align along functional stress (Wolff’s law). Children remodel angulation and some deformity more effectively than adults, particularly near a growing physis; rotational deformity and large displacement remodel poorly at any age. Remodelling may continue long after the patient is clinically functional.

4. Primary (direct) fracture healing

Primary healing requires near-anatomic reduction, minimal fracture gap and very rigid fixation that reduces interfragmentary strain. There may be little or no visible external callus. Cutting cones of osteoclasts cross the fracture from existing Haversian systems, followed by osteoblasts that create new osteons and restore the cortex. Contact healing occurs when the gap is extremely small; gap healing fills a small space with woven bone that later remodels. If fixation is not sufficiently rigid, a fracture intended to heal primarily may instead develop a secondary callus or progress to delayed union.

5. Mechanical environment and interfragmentary strain

Mechanical condition	Biological response	Clinical implication
Very small gap, rigid stability and low strain	Direct osteonal healing	Typical of accurately reduced, compression-type fixation
Controlled relative motion with adequate vascularity	Callus-mediated secondary healing	Common with splints, casts, intramedullary nails and bridge plating
Excessive motion, large gap or instability	Persistent fibrous tissue, pain and possible non-union	Check alignment, fixation, weight-bearing plan and infection
Very low strain but devascularised tissue	Little biological response despite stability	Restore soft-tissue perfusion and remove necrotic or infected tissue

Healing is therefore a balance: enough stability to permit vascular ingrowth and tissue maturation, but not necessarily absolute immobility in every fracture. The correct mechanical plan depends on bone, location, fracture pattern, patient factors and the chosen fixation.

6. Expected clinical and radiographic progression

Stage	Clinical findings	Imaging/pathology
Early injury	Pain, tenderness, swelling, bruising and instability	Fracture line; soft-tissue injury; haematoma not always visible on plain film
Soft callus	Pain and motion gradually reduce but loading may still hurt	Early periosteal reaction or faint callus; fracture line persists
Hard callus/bridging	Progressive painless function and stability	Mineralised bridging callus in several cortices; fracture line becomes less distinct
Remodelling	Strength and movement continue to improve	Callus becomes more compact and aligned; medullary canal reforms

Do not diagnose union from a single feature. Combine pain on loading, tenderness, abnormal movement, functional progress, serial radiographs and the specific bone’s expected timeline. If symptoms worsen, a new fracture line becomes visible or alignment changes, reassess urgently.

7. Factors that affect healing

7.1 Local factors

• Bone and anatomical blood supply: scaphoid, talus, femoral neck and some tibial regions are vulnerable to avascular necrosis or delayed union.
• Fracture pattern: transverse, comminuted, segmental, oblique and intra-articular patterns have different stability and surface-area demands.
• Gap, displacement, interposed muscle or periosteum, rotational instability and excessive shear.
• Open injury, crushing, stripping of periosteum, skin loss and thermal damage.
• Infection, retained foreign body, dead bone, implant loosening or biofilm.
• Radiotherapy or local tumour, severe oedema, compartment syndrome and repeated surgical disruption.

7.2 Systemic factors

• Age: children generally heal faster; older adults often have reduced osteogenic capacity and vascular reserve.
• Smoking and nicotine-related vasoconstriction, carbon monoxide exposure and impaired osteoblast function.
• Diabetes, peripheral vascular disease, renal disease, anaemia and chronic hypoxia.
• Malnutrition, low protein intake, vitamin D deficiency and disorders of calcium, phosphate or parathyroid hormone.
• Immunosuppression, infection elsewhere and severe systemic illness.
• Medications: prolonged corticosteroid exposure can impair bone formation; decisions about analgesic and anti-inflammatory medicines should balance fracture healing with safe pain control and follow local protocol.
• Non-adherence, premature high loading, poor access to follow-up and inadequate physiotherapy.

7.3 Modifiable protective measures

• Early haemorrhage control, gentle tissue handling and preservation of periosteal/soft-tissue attachments.
• Prompt irrigation and debridement for open fractures, tetanus assessment and antibiotics according to local protocol.
• Stable alignment and fixation appropriate to the injury, with a documented weight-bearing plan.
• Smoking cessation, adequate protein/energy intake, correction of severe vitamin D or calcium abnormalities and optimisation of diabetes and vascular disease.
• Serial clinical and radiographic review rather than assuming that a cast or implant guarantees union.

8. Open fractures: why emergency care changes the biology

An open fracture connects the fracture haematoma or bone to the outside environment. The wound may be small while deep contamination and vascular injury are extensive. Treat it as a limb-threatening injury until assessed:

1. Use trauma resuscitation principles and control life-threatening bleeding.
2. Document wound size, contamination, pulses, capillary refill, sensation and motor function; repeat examinations after splinting or reduction.
3. Cover with a sterile saline-moistened dressing; do not repeatedly probe or close the wound in the emergency area.
4. Give early antibiotics and tetanus prophylaxis according to local guideline and allergy status.
5. Splint in a safe position, provide analgesia, obtain appropriate imaging and arrange urgent orthopaedic/plastic-surgical assessment for operative irrigation, debridement and stabilisation.
6. Look actively for compartment syndrome, vascular injury, nerve/tendon damage and contamination with soil, water, sewage or animal/human bites.

9. Disorders of union

Delayed union

Healing is slower than expected for the bone and injury, but progressive union is still occurring. Pain or tenderness persists and radiographs show limited but advancing callus. Recheck infection, alignment, stability, smoking, nutrition and endocrine/metabolic disease before labelling a fracture as non-union.

Non-union

Non-union is failure of progressive healing within the expected clinical context, with persistent motion, pain and no convincing progression on serial studies. Terminology varies by jurisdiction and bone; use the treating orthopaedic team’s definition. Common biological causes include infection, avascular fragments, nicotine, severe tissue injury and systemic disease. Mechanical causes include a persistent gap, malalignment, inadequate fixation or excessive motion.

• Hypertrophic non-union: abundant callus but inadequate stability (“elephant-foot” or “horse-hoof” patterns); mechanical stability is the dominant problem.
• Atrophic non-union: little callus and poor biology, often with devascularisation, infection or a large gap; requires biological as well as mechanical correction.
• Oligotrophic non-union: limited callus, often with distraction or poor reduction.

Malunion

Malunion is union in an unacceptable position—angulation, shortening, translation or rotation. Functional effect depends on bone and joint. Rotational deformity is poorly tolerated and commonly needs specialist correction. Children may remodel some angular deformity, but that does not justify accepting severe displacement or malrotation.

10. Complications that can mimic poor healing

• Complex regional pain syndrome, neuropathic pain or tendon adhesions.
• Hardware irritation, loosening, breakage or peri-implant fracture.
• Deep venous thrombosis, fat embolism syndrome or pulmonary complications after major long-bone trauma.
• Osteomyelitis, chronic sinus and implant-associated infection.
• Joint stiffness, muscle wasting and loss of function from prolonged immobilisation.
• Compartment syndrome, which is an emergency and not a normal phase of healing.

11. Emergency clinical reasoning

12. Cases

Case 1: Closed tibial shaft fracture

A patient has swelling and deformity but intact pulses and sensation. After analgesia, alignment is supported and the limb is splinted. Serial examination is essential because swelling can evolve and compartment syndrome may appear after the first assessment. Healing is usually secondary, with callus, but union depends on soft-tissue preservation, alignment and appropriate stability.

Case 2: Open contaminated tibial fracture

A wound exposes bone after a road-traffic collision. The priority is resuscitation, sterile coverage, early antibiotics and tetanus assessment, neurovascular documentation, splinting and urgent operative debridement—not bedside closure. Infection and devascularisation can convert a potentially healing fracture into a chronic non-union.

Case 3: Painful fracture months after fixation

Persistent pain, tenderness, implant stress or absent serial bridging should trigger assessment for delayed union or non-union. Review smoking, diabetes, nutrition, infection, fixation stability and alignment. Do not simply prescribe more immobilisation without identifying the biological or mechanical cause.

13. High-yield distinctions

Term	Meaning	Typical clue
Callus	Repair tissue, first soft then mineralised	Prominent in secondary healing
Union	Progressive biological and mechanical bridging	Less tenderness and abnormal movement with serial radiographic progression
Delayed union	Slower-than-expected but ongoing repair	Some progression, not complete failure
Non-union	Failure of progressive repair	Persistent motion/pain with stagnant serial imaging
Malunion	Healed in an unacceptable position	Angulation, shortening or rotation after union

References and further reading

• NCBI Bookshelf: Fracture Healing Overview.
• NCBI Bookshelf: Bone healing biology and complications.
• NCBI Bookshelf: Open Fracture Management.
• Follow local orthopaedic, trauma, antimicrobial and tetanus protocols; timelines and operative decisions vary with bone, injury severity and available specialist care.