7.5.2 Bone Repair

Bone is a living tissue that undergoes repair following fracture. The repair process of a simple fracture takes place in four major steps.

Haematoma or Clot Formation

• When a bone breaks, blood vessels in the bone, and perhaps in surrounding tissues, are torn and haemorrhage.
• As a result, a haematoma, a mass of clotted blood, forms at the fracture site.
• Soon, bone cells deprived of nutrition die, and the tissue at the site becomes swollen, painful, and inflamed.

Fibrocartilaginous Callus Formation

• Within a few days, several events lead to the formation of fibrocartilaginous or soft callus.
• Capillaries grow into the haematoma and phagocytic cells invade the area and begin cleaning up the debris.
• A fracture ruptures the periosteum and stimulates the production and release of the numerous osteoblasts.
• These osteoblasts in conjunction with cartilage forming cells secrete a porous mass of bone and cartilage called callus (or cartilaginous callus) surrounding the break.
• The callus replaces the original blood clot and holds the ends of the bones together.
• This process takes 3-4 weeks.

Bony Callus Formation or Callus Ossification

• Within a week, after the formation of soft callus, it is gradually converted into a hard bony callus of spongy bone.
• Bony callus formation continues until a firm union is formed about two months later.
• Osteoclasts breakdown the cartilage while osteoblasts replace it with bone.

Bone Remodelling

• It takes place when a compact bone is formed across the fracture line to connect both sides.
• Usually, more bone is produced at the site of a healing fracture than needed to replace the damaged tissue.
• However, osteoclasts eventually remove the excess and the final result of the repair is bone shaped very much like the original.
• The final structure of the remodeled area resembles that of the original unbroken bony region because it responds to the same set of mechanical stressors.

Science, Technology and Society Connections

Relate improper posture to bone/joint problems.

- Improper posture causes increased stress on joints and their supporting structures resulting in injury, pain and early degeneration of bones and joints.

Summary Table of Fracture Types

Summary Table of Bone Repair

Intermediate Level

Types of Fractures

Steps of Bone Repair

Cells Involved in Bone Repair

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. Fracture is a broken bone.
• 2. Fractures occur when force exceeds bone strength.
• 3. Simple fracture: skin is intact.
• 4. Compound fracture: bone ends penetrate skin.
• 5. Complicated fracture: damages adjacent organs.
• 6. Bone is a living tissue.
• 7. Bone undergoes repair following fracture.
• 8. Repair process has four major steps.
• 9. Step 1: Haematoma formation.
• 10. Step 2: Fibrocartilaginous callus formation.
• 11. Step 3: Bony callus formation.
• 12. Step 4: Bone remodelling.
• 13. Haematoma is a mass of clotted blood.
• 14. Fibrocartilaginous callus is a porous mass of bone and cartilage.
• 15. Bony callus is hard spongy bone.
• 16. Bone remodelling forms compact bone across fracture line.
• 17. Osteoblasts form new bone.
• 18. Osteoclasts break down cartilage and excess bone.
• 19. Improper posture causes stress on joints.
• 20. Improper posture leads to early degeneration.

Remember

• - Fracture = broken bone
• - Simple fracture = skin is intact
• - Compound fracture = bone ends penetrate the skin
• - Complicated fracture = fracture damages adjacent organs
• - Haematoma = mass of clotted blood
• - Fibrocartilaginous callus = soft callus; porous mass of bone and cartilage
• - Bony callus = hard callus; spongy bone
• - Bone remodelling = final step; compact bone formed across fracture line
• - Osteoblasts = form new bone
• - Osteoclasts = break down cartilage and excess bone

Common Mistakes

• 1. Confusing simple and compound fractures — Simple = skin intact; compound = bone penetrates skin.
• 2. Mixing up the steps of bone repair — Haematoma, soft callus, hard callus, remodelling.
• 3. Forgetting the duration of steps — Soft callus: 3-4 weeks; hard callus: about 2 months.
• 4. Mixing up osteoblasts and osteoclasts — Osteoblasts = build bone; osteoclasts = break down bone.
• 5. Thinking bones do not heal — Bones are living tissue and can heal.
• 6. Forgetting the role of phagocytic cells — Clean up debris.
• 7. Confusing complicated fracture with compound fracture — Complicated = damages organs; compound = penetrates skin.
• 8. Believing bone remodelling is the first step — Remodelling is the final step.
• 9. Mixing up the types of fractures — Simple, compound, complicated.
• 10. Thinking improper posture only affects muscles — Improper posture also affects bones and joints.

Quick Revision

A fracture is the medical term for a broken bone. They occur when the physical force exerted on the bone is stronger than the bone itself. So bones break when they cannot withstand a force or trauma applied to them. Simple fracture or closed fractures are those in which the skin is intact. If the bone ends penetrate the skin and form a wound are called compound fracture or open fracture. When a fracture damages the adjacent organs it is called complicated fracture. Bone is a living tissue that undergoes repair following fracture. The repair process of a simple fracture takes place in four major steps. Haematoma or clot formation: When a bone breaks, blood vessels in the bone, and perhaps in surrounding tissues, are torn and haemorrhage. As a result, a haematoma, a mass of clotted blood, forms at the fracture site. Fibrocartilaginous callus formation: Within a few days, several events lead to the formation of fibrocartilaginous or soft callus. This process takes 3-4 weeks. Bony callus formation or callus ossification: Within a week, after the formation of soft callus, it is gradually converted into a hard bony callus of spongy bone. Bony callus formation continues until a firm union is formed about two months later. Bone remodelling: It takes place when a compact bone is formed across the fracture line to connect both sides.

60-Second Revision

• Fracture = broken bone
• Simple fracture = skin is intact
• Compound fracture = bone ends penetrate the skin
• Complicated fracture = fracture damages adjacent organs
• Haematoma = mass of clotted blood
• Fibrocartilaginous callus = soft callus; porous mass of bone and cartilage
• Bony callus = hard callus; spongy bone
• Bone remodelling = final step; compact bone formed across fracture line
• Osteoblasts = form new bone
• Osteoclasts = break down cartilage and excess bone
• Warning: Bone is a living tissue that undergoes repair following fracture

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