Physiology of Fracture Healing

Question 1

What does primary bone healing involve?

Answer 1

Involves the bone simply bridges the gap with new bone from osteoblasts

Question 2

What fractures have primary bone healing?

Answer 2

-Hairline fractures (minimal fracture gap of less than about 1mm)
-Fractures fixed with compression screws and plates

Question 3

What does secondary bone healing involve?

Answer 3

Involves an inflammatory response with recruitment of pluropotential stem cells which differentiate into different cells during the healing process

Question 4

What fractures have secondary bone healing?

Answer 4

In the majority of fractures, when there is a gap at the fracture site which needs to be filled temporarily to act as a scaffold for new bone to be laid down

Question 5

Describe first steps that occur in debridement of secondary bone healing

Answer 5

1. Fracture occurs
2. Haematoma occurs with inflammation from damaged tissues
3. Macrophages and osteoclasts remove debris and resorb the bone ends
4. Granulation tissue forms from fibroblasts and new blood vessels

Question 6

Describe steps that lead from soft callus formation to hard callus formation to remodelling of bone

Answer 6

5. Chondroblasts form cartilage (soft callus)
   
   1. Usually formed by the 2nd-3rd week
6. Osteoblasts lay down bone matrix (collagen type 1) - enchondral ossification
7. Calcium mineralisation produces immature woven bone (hard callus)
   
   1. Takes approximately 6-12 weeks
8. Remodelling occurs with organization along lines of stress into lamellar bone

Question 7

What things do secondary bone healing require?

Answer 7

• Secondary bone healing requires a good blood supply for oxygen, nutrients and stem cells and also requires a little movement or stress (compression or tension)
  
  • A lack of blood supply, no movement (internal fixation with fracture gap), too big a fracture gap or tissue trapped in the fracture gap may result in an atrophic non‐union
• Smoking may severely impair fracture healing due to vasospasm whilst vascular disease, chronic ill health and malnutrition will also impair fracture healing
• Hypertrophic non-unions occur due to excessive movement at the fracture site with abundant hard callus formation