Anatomy and Physiology 2e · Bone Tissue and the Skeletal System
Fractures: Bone Repair
On this page 9 sections
In 30 seconds
A Fracture Any break or crack in a bone Full entry → is any break in a bone — hairline crack to shattered shaft — and bone is one of the few tissues that heals by regenerating true bone rather than scar tissue. This topic covers fracture classification (by pattern and by whether the skin is broken) and the four-stage repair process: hematoma, Fibrocartilaginous callus Soft bridge of fibrous tissue and cartilage joining fragments Full entry →, Bony callus Woven bone that replaces the soft callus Full entry →, Remodeling Resorption and redeposition reshaping the callus into normal bone Full entry →. That sequence is a classic exam path and a practical model for why healing takes months, why some fractures heal poorly, and what casting, traction, and internal fixation do.
Why this matters
Fractures are among the most common emergency visits, and the repair sequence explains treatment logic and complications. Closed reduction (manual alignment) works because the callus will later bridge a well-aligned gap; open reduction with internal fixation (plates, screws, rods) is chosen for unstable, comminuted, or open fractures. Knowing open fractures are contaminated explains why they receive urgent wound care before orthopedic repair. The same four stages govern stress fractures in athletes and osteoporotic fragility fractures, and the remodeling stage is why children's fractures may heal with less-than-perfect alignment — remodeling corrects it. Classic complications to monitor — infection (especially open fractures), fat embolism, compartment syndrome, delayed/Nonunion Failure of a fracture to heal/bridge Full entry → — are part of routine fracture care, though protocols vary by institution and should follow current guidance.
The college version
Core Concepts
Classifying fractures
Fractures are named by appearance and mechanism. Common patterns:
- Transverse fracture — the break runs straight across the bone.
- Oblique fracture — the break runs diagonally across the bone.
- Spiral fracture — the fracture line twists around the shaft, typically from a rotational force; an important pattern to recognize because it can raise questions about how the injury occurred.
- Comminuted fracture Bone shattered into three or more pieces Full entry → — the bone shatters into three or more fragments; common in high-energy impacts and in older adults with weakened bone.
- Impacted fracture — one fragment is driven into another, as when a fall compresses the end of a bone.
- Greenstick fracture Incomplete break on one side, bending on the other Full entry → — an incomplete break on one side of the bone, with the other side bending; seen in children because their bones are more flexible and incompletely mineralized.
A separate, crucial distinction is open (compound) versus closed (simple): in an open fracture the bone pierces or is exposed through the skin, creating a route for infection and significant blood loss; in a closed fracture the skin stays intact. Open fractures are managed as contaminated wounds.
Stage 1: Hematoma formation
When a bone breaks, vessels in the periosteum, marrow, and bone itself tear; the escaping blood clots at the site, forming a Fracture hematoma Blood clot that forms at the fracture site Full entry → within hours. The hematoma is more than a clot — it is the scaffold and signaling environment for repair, and the inflammatory response it triggers produces the visible swelling and pain.
Stage 2: Fibrocartilaginous callus formation
Within days, capillaries grow into the hematoma as fibroblasts and chondroblasts arrive, producing collagen and cartilage that bridge the gap as a fibrocartilaginous callus. Meanwhile the periosteum builds an external callus of new bone and cartilage around the site, splinting the bone like a natural cast. This callus is not yet bone — a loose mix of fibrous tissue and cartilage holding the fragments together.
Stage 3: Bony callus formation
About one to two weeks after injury, osteoblasts invade the callus and deposit bone on its cartilage and fibrous scaffolds — a process echoing endochondral and intramembranous ossification — producing a bony callus of woven (immature) bone. Within roughly two months the fragments are firmly united: structurally continuous, but bulky and not yet shaped like the original bone.
Stage 4: Bone remodeling
In the final stage, lasting months, the woven callus is remodeled into mature lamellar bone: osteoclasts resorb the excess while osteoblasts deposit new bone along lines of stress, restoring original shape and strength — until the fracture site may become radiographically invisible. The same machinery that maintains the skeleton (Topics 3 and 7) does the sculpting.
Factors that affect healing
Healing depends on age (children remodel faster), blood supply (poorly vascularized sites heal slowly or fail), nutrition (calcium, vitamin D, protein, vitamin C), hormones, and general health — smoking and poorly controlled diabetes are linked to delayed or failed union. Poorly aligned fragments can heal as Malunion Healing with fragments in an incorrect position Full entry → (deformed position) or nonunion (never bridging), so fractures are reduced — aligned — before or during immobilization.
Common Confusions
| Do Not Confuse | With | The Difference |
|---|---|---|
| Open fracture | Closed fracture | Open = bone breaks through skin (infection risk, emergency); closed = skin intact |
| Greenstick fracture | Complete fracture | Greenstick is incomplete (one side breaks, other bends) — children only; complete goes all the way through |
| Oblique fracture | Spiral fracture | Oblique is a straight diagonal line; spiral twists around the shaft from rotational force |
| Fibrocartilaginous callus | Bony callus | Soft callus = fibrous tissue + cartilage (first weeks); bony callus = woven bone replacing it (by ~2 months) |
| Reduction | Remodeling | Reduction is the initial realignment; remodeling is the months-long reshaping of the healed bone |
| Osteoblasts during repair | Osteoclasts during repair | Osteoblasts build the callus bone; osteoclasts resorb excess callus during remodeling |
Eli explains
The same idea, in plain words
Explain it like I’m 10
When a bone breaks, your body fixes it like a road crew fixing a broken sidewalk. First, blood fills the crack and forms a jelly-like clot. Then the body builds a soft "bump" of squishy material (like clay) to hold the pieces together. Next, it replaces the clay with a rough chunk of new bone, like quick-drying concrete. Finally, workers smooth the extra concrete away so the sidewalk looks almost new — that smoothing step takes the longest.
Worked example
A 24-year-old skier catches an edge and her leg twists violently. She hears a snap; X-ray shows a spiral fracture of the tibia — closed. The team performs a closed reduction (alignment under sedation) and applies a long-leg cast. Walk the timeline: within 48 hours the fracture hematoma forms — the swelling she feels. Within a week, fibroblasts and chondroblasts are building the fibrocartilaginous callus; by two weeks, osteoblasts are converting it to a bony callus, visible at her six-week X-ray as a bulky white mass bridging the fracture line. She keeps weight off the leg — woven bone is not yet strong. Over months, osteoclasts and osteoblasts remodel the callus; by nine months the fracture line is nearly invisible and she returns to skiing. Because the fracture was rotational, the clinicians also documented the mechanism carefully — a standard part of evaluating this pattern.
Key takeaways
- Fracture patterns: transverse, oblique, spiral, comminuted, impacted, greenstick; plus the all-important open vs closed distinction.
- Greenstick = incomplete, children; comminuted = 3+ fragments; spiral = twisting forces.
- Repair sequence (memorize in order): hematoma → fibrocartilaginous callus → bony callus → remodeling.
- The bony callus forms in ~1–2 weeks and unites fragments in ~2 months; remodeling takes months.
- Open (compound) fractures carry infection risk and are managed as contaminated wounds.
- Healing depends on alignment (reduction), blood supply, age, nutrition (calcium, vitamin D, protein, vitamin C), and avoidance of smoking.
- Malunion and nonunion are the two main failures of healing.
Check yourself
5 review questions from the chapter. Try each one, then open the answer.
List the four stages of bone repair in order, and state roughly when each begins.
Show answer
(1) Hematoma formation (within hours), (2) fibrocartilaginous callus formation (within days), (3) bony callus formation (1–2 weeks, fragments united by ~2 months), (4) bone remodeling (months).
Why is an Open (compound) fracture Fracture in which bone breaks through the skin Full entry → treated as a more urgent emergency than a closed fracture?
Show answer
Because the broken bone is exposed, creating a direct route for bacteria to reach the wound — infection risk — and there may be significant blood loss; urgent wound care is needed in addition to fracture management.
Which fracture type would you expect from a twisting injury, and which from a fall that drives one bone end into another?
Show answer
Spiral fracture from a twisting/rotational force; impacted fracture when one fragment is driven into another by compression.
Why do children's greenstick fractures heal differently from adult fractures?
Show answer
Children's bones are more flexible and less mineralized, so they bend and crack incompletely (greenstick) rather than snap; children also remodel faster and tolerate less-perfect alignment because remodeling corrects it.
What is the difference between malunion and nonunion, and what factors raise the risk of nonunion?
Show answer
Malunion is healing with fragments in a wrong position (deformity); nonunion is failure to bridge at all. Risk factors: poor blood supply, infection, smoking, inadequate immobilization.
Study tools & related lessonsKey vocabulary · Related
Key vocabulary
- Fracture
- Any break or crack in a bone
- Open (compound) fracture
- Fracture in which bone breaks through the skin
- Greenstick fracture
- Incomplete break on one side, bending on the other
- Comminuted fracture
- Bone shattered into three or more pieces
- Fracture hematoma
- Blood clot that forms at the fracture site
- Fibrocartilaginous callus
- Soft bridge of fibrous tissue and cartilage joining fragments
- Bony callus
- Woven bone that replaces the soft callus
- Remodeling
- Resorption and redeposition reshaping the callus into normal bone
- Malunion
- Healing with fragments in an incorrect position
- Nonunion
- Failure of a fracture to heal/bridge
Sources & references
This lesson was adapted from the open educational references above; their licenses and attributions are preserved. See Copyright & Licensing.
Educational content only. It is not medical, legal or professional advice. Found an error? Tell us.