Orthopedics
Fracture Healing
Hematoma, callus, remodeling — how broken bone reconstitutes itself
Fractured bone heals through four overlapping phases. Hematoma (hours to days) — bleeding and inflammation; cytokines (TNF-alpha, IL-1, IL-6) recruit cells. Soft callus or fibrocartilaginous callus (1-3 weeks) — fibroblasts and chondroblasts deposit type II collagen and cartilage; bridges the fracture. Hard callus (3-12 weeks) — endochondral ossification converts cartilage to woven bone via osteoblasts; visible on X-ray as callus. Remodeling (months to years) — osteoclasts resorb woven bone, osteoblasts lay down lamellar bone along Wolff's law lines of stress. Healing time depends on bone, fracture pattern, age, blood supply. Risk factors for nonunion — smoking, NSAIDs, diabetes, infection, inadequate immobilization. Bisphosphonates and atypical femur fractures are a known complication.
- Hematoma phaseHours to days; cytokine release
- Soft callus1-3 weeks; fibrocartilage
- Hard callus3-12 weeks; woven bone
- RemodelingMonths to years; lamellar bone
- Wolff's lawBone adapts to mechanical loading
- Nonunion thresholdNo healing at 6-9 months
Interactive visualization
Press play, or step through manually. The visualization is yours to drive — try it before reading on.
Watch the 60-second explainer
A condensed visual walkthrough — narrated, captioned, under a minute.
Why fracture healing matters
- Trauma management. Determines surgical timing and immobilization.
- Osteoporosis care. Hip and vertebral fractures drive disability and mortality.
- Athletic injuries. Stress fractures and return-to-play timing.
- Pediatric growth. Physeal injuries can cause limb-length discrepancy.
- Smoking cessation counseling. Demonstrably worsens healing.
- Drug interactions. Steroids, NSAIDs, fluoroquinolones affect bone biology.
- Diabetic care. Charcot foot and impaired healing.
Common errors
- NSAIDs early after fracture. May impair callus formation; avoid first 1-2 weeks.
- Late operation on hip fracture. Delay >48 hours increases mortality.
- Closed treatment of displaced femoral neck fracture. High AVN risk; needs prompt fixation or arthroplasty.
- Missing compartment syndrome. Pain out of proportion, paresthesias, pallor, pulselessness, paralysis — fasciotomy emergency.
- Treating osteoporosis fracture without bone health workup. Vitamin D, calcium, DEXA, bisphosphonate or denosumab.
- Ignoring open fracture as urgent. Antibiotics within 1 hour, OR within 24 hours; otherwise infection.
Frequently asked questions
What's the difference between primary and secondary healing?
Primary (direct) healing — rigid fixation with compression plate; no callus; cutting cones of osteoclasts cross fracture line; osteoblasts follow with new lamellar bone. Slower radiographic healing but mechanically strong. Secondary (indirect) healing — most fractures with cast or relative stability; classic four-phase callus formation. Visible callus on X-ray. Either path achieves union; surgeon chooses based on fracture, function, and biology.
Why do some fractures fail to heal?
Nonunion (>6-9 months without healing) results from instability, poor blood supply, infection, gap, or biology. Atrophic — biology problem; treat with autograft, BMP-2 or BMP-7, smoking cessation. Hypertrophic — mechanical problem; abundant callus but no bridging; treat with rigid fixation. Risk factors — smoking (doubles nonunion risk), diabetes, NSAIDs in early healing, malnutrition, vitamin D deficiency, infection, open fracture, segmental bone loss.
When should you operate on a fracture?
Open fractures (Gustilo-Anderson grades) require urgent irrigation, debridement, antibiotics within hours. Displaced intra-articular fractures need anatomic reduction. Hip fractures in elderly — surgery within 24-48 hours improves mortality. Femoral shaft, tibial shaft, both bone forearm, displaced clavicle in active patients, unstable spine. Conservative care fits stable, minimally displaced, well-aligned fractures — distal radius (Colles), most clavicle, ribs, toes, simple distal fibula.
How do steroids and NSAIDs affect healing?
Glucocorticoids impair osteoblast function and reduce bone formation — chronic users have higher nonunion rates and osteoporotic fractures (>5 mg prednisone for >3 months). NSAIDs inhibit COX-2; animal studies and some clinical data suggest impaired callus formation when used in first 1-2 weeks. Selective COX-2 inhibitors implicated more strongly. Most surgeons avoid NSAIDs early; use acetaminophen or short opioids for pain.
What is a stress fracture?
Fatigue failure from repetitive submaximal loading. Common in metatarsals (march fracture), tibia, navicular, femoral neck. Risk factors — sudden activity increase, female athlete triad (low energy availability, menstrual dysfunction, low bone density), poor footwear, vitamin D deficiency. X-ray often negative early; MRI sensitive within days. Treatment — relative rest, activity modification, addressing underlying causes. Femoral neck stress fractures on tension side require surgery to prevent displacement.
How do bisphosphonates affect bones?
Alendronate, risedronate, zoledronate inhibit osteoclasts. Reduce vertebral, hip, and nonvertebral fractures by 30-50% in osteoporosis. Long-term use (>5 years) associated with atypical femur fractures (subtrochanteric or diaphyseal, transverse pattern, with prodromal thigh pain) and osteonecrosis of the jaw (especially with dental procedures and IV bisphosphonates). Drug holiday after 5 years of oral or 3 years of IV use considered for low-risk patients.
What about pediatric fractures?
Children's bones are more porous, less brittle, and remodel powerfully. Greenstick fractures — incomplete cortical break on tension side. Buckle (torus) — incomplete compression failure. Plastic deformation — bowing without break. Salter-Harris classification (I-V) describes physeal injuries; types III, IV, V risk growth disturbance. Healing is fast — 4-6 weeks for most fractures. Remodeling can correct angulation if same plane as joint motion and physis still open.