Bone Growth and Fracture Healing

Question 1

What are the differences between Cortical and Cancellous bone?

Answer 1

Cortical

• Diaphysis
• Resists - bending and torsion.
• laid down circumferentially
• less biologically active.

Cancellous

• metaphysis
• Resists and absorbs - compression
• Site of longitudinal growth (physis)
• very biologically active

Question 2

What is a fracture?

Answer 2

Break in structural continuity of bone. May be a crack, break, split, crumpling or buckle.

Question 3

What is the biology of a fracture?

Answer 3

Mechanical and structural failure of bone.
Disruption of blood supply.
Regenerative 4 stage process with no scarring.

Question 4

What is stage 1 of fracture healing?

Answer 4

Inflammation

Begins immediately after fracture. Haematoma and fibrin clot are formed. Platelets, PMNs (polymorphonuclear neutrophils), Neurtrophils, monocytes and macrophages are all involved. By products of cell death are also broken down by lysosomal enzymes.
Fibroblasts are then signalled as well as mesenchymal and osteoprogenitor cells. Angiogenesis occurs, requiring a low oxygen gradient and macrophages aid this by producing angiogenic factors under hypoxic conditions.

Question 5

What are Mesenchymal and osteoprogenitor cells?

Answer 5

Transformed endothelial cells from medullary canal of bone and/or periosteum. Osteogenitor cells then induce cells from muscle and soft tissues.

Question 6

What is stage 2 of fracture healing?

Answer 6

Soft callus

Begins when pain and swelling subside.
Lasts until bony fragments are united by cartilage or fibrous tissue. Provides some stability to the fracture. Continued increase in vasculature.

Question 7

What is an autogenous cancellous bone graft?

Answer 7

Utilises bone obtained from the same individual receiving the graft. It is osteoconductive and osteoinductive.
Gold standard treatment.

Question 8

What is meant when it is said a graft is osteoconductive?

Answer 8

The bone graft material serves as a scaffold for new bone growth that is perpetuated by the native bone.

Question 9

What is meant when it is said a bone graft is osteoinductive?

Answer 9

Involves the stimulation of osteoprogenitor cells to differentiate into osteoblasts that then begin new bone formation.

Question 10

What is allograft bone?

Answer 10

Bone derived from humans but not from the individual receiving the graft. Can be taken from cadavers or live donors.

Question 11

What is stage 3 of fracture healing?

Answer 11

Hard callus

Conversion of cartilage to woven bone.
Typical long bone fracture - endochondral and
membranous bone formation.
Increases rigidity.

Question 12

What is stage 4 of fracture healing?

Answer 12

Bone remodelling

Conversion of woven bone to lamellar bone. Medullary canal is reconstituted. Bone responds to loading characteristics.

Question 13

What is Wolff’s law?

Answer 13

Bone in a healthy person or animal will adapt to the loads under which it is placed.

Question 14

How does strain affect fracture healing?

Answer 14

If strain is too low then mechanical induction of tissue differentiation fails.
If strain is too high then healing process does not progress to bone formation.

Question 15

What is delayed union?

Answer 15

Failure to heal in expected time.

Question 16

What are some causes of delayed union?

Answer 16

High energy injury
Instability
Infection 
Steroids
Immune suppressants
Smoking
Warfarin
NSAID
Ciprofloxacin
Distraction - increased osteogenic jumping.

Question 17

What is non union?

Answer 17

Failure to heal

Question 18

What are some causes of non union?

Answer 18

Failure to calcify fibrocartilage
Instability - excessive osteoclasis
Abundant callus formation
Pain + tenderness
Persistant fracture line
Sclerosis

Question 19

What are some management option for delayed healing?

Answer 19

Different fixation
Dynamisation - promotes bone healing through movements and some compressive loading.
Bone grafting

Question 20

What is the Gustilo classification of open fractures?

Answer 20

Type 1 - Wound <1cm, clean, simple fracture pattern.

Type 2- Wound >1cm, moderate soft tissue damage, adequate skin coverage, simple fracture pattern.

Type 3 - Extensive soft tissue damage, complex fracture pattern.
3A- adequate periosteal coverage.
3B - tissue loss requiring soft tissue coverage procedure.
3C - vascular injury requiring repair.

Question 21

What is the management of fractures?

Answer 21

Full MDT assessment
Tetanus and antibiotic prophylaxis.
Cefuroxime/Augmentin/Clindamycin at time of fixation.
Repeated examination of neuromuscular status.
No provisional irrigation/exploration
Radiographs of joint and above and below.

Question 22

What are the indications for emergency fracture surgery?

Answer 22

Polytraumatised patient
Marine or farmyard environment
Gross contamination
Neurovascular compromise
Compartment syndrome.

Question 23

What criterion must be met before amputation?

Answer 23

Dual consultant decision
Insensate limb/foot
Irretrievable soft tissue or bony damage
Other life threatening injuries
Guillotine type and refashion at later stage.