Bone Growth and Fracture Healing

Question 1

Describe a summary of bone growth

Answer 1

Hyaline cartilage model
Then gets primary ossification centre and secondary ossification centre
Then medullary cavity
Then epiphyseal plate at end of long bones - allowing to continue to grow

Question 2

Describe long bone anatomy

Answer 2

Diaphysis (shaft), metaphysis (flare at end), epiphysis, physis growth plate and medullary canal

Question 3

Describe cortical bone

Answer 3

Mainly in diaphysis, resists bending and torsion, laid down circumferentially and less biologically active

Question 4

What is cancellous bone?

Answer 4

Spongy bone

Question 5

Describe cancellous bone

Answer 5

Mainly in metaphysis, resist/ absorbs compression, site of longitudinal growth and very biologically active

Question 6

What is a fracture?

Answer 6

Break in structural continuity in bone
Crack, break, split, crumple and buckle
# - means fracture in notes

Question 7

Why do bones fail?

Answer 7

High energy transfer in normal bones - takes a lot
Repetitive stress - stress fractures
Low energy transfer - osteoporosis, osteomalacia and metastatic tumour

Question 8

Describe the fracture biology

Answer 8

No scar and has 4 stages of regeneration
Disruption of blood supply
Mechanical and structural failure of bone

Question 9

Describe stage 1 of regeneration of bone - inflammation

Answer 9

Begins immediately after fracture
Haematoma and fibrin clot
Platelets, PMNs, neutrophils, monocytes and macrophages
By products of cell death - lysosomal enzymes

Question 10

What cells are involved in stage 1 inflammation?

Answer 10

Fibroblasts
Mesenchymal and osteoprogenitor cells
Angiogenesis occurs - macrophages produce angiogenic factors under hypoxic conditions

Question 11

What is the role of mesenchymal and osteoprogenitor cells in stage 1 inflammation?

Answer 11

Transformed endothelial cells from medullary canal or periosteum
Osteogenic induction of cells from muscle and soft tissue

Question 12

What can be done to affect the inflammation stage of bone regeneration?

Answer 12

NSAIDs
Loss haematoma - open fractures and surgery
Extensive tissue damage - poor blood supply

Question 13

What do platelet concentrates do?

Answer 13

Platelets release platelet derived GF, Transforming growth factor-beta, IGF, and VEGF which are important in brining in cells for healing

Question 14

Describe the soft callus phase - stage 2

Answer 14

Begins when pain and swelling subside
Lasts until bony fragments are united by cartilage or fibrous tissue
Some stability - angulation can still occur
Increase in vascularity

Question 15

How might we affect soft callus?

Answer 15

Replace cartilage - DMB (demineralised bone matrix)
Jump straight to bone - bone graft and bone substitutes

Question 16

What is a autogenous cancellous bone graft?

Answer 16

Gold standard
Osteo-conductive - structure where cells can grow through it
Osteo-inductive

Question 17

What are the types of allograft bone?

Answer 17

Cortical, cancellous, fresh, prepared and structural

Question 18

Describe a allograft bone

Answer 18

Osteo- conductive
Not osteo-inductive
Creeping substitution - replaced by new bone growing in
Risk of disease transmission

Question 19

Describe stage 3 - hard callus

Answer 19

Conversion of cartilage to woven bone
Typical long bone fracture - endochondral and membranous bone formation
Increasing rigidity - secondary bone healing and obvious callus

Question 20

Describe stage 4 - bone remodelling

Answer 20

Conversion of woven bone to lamellar bone
Medullary canal is reconstituted
Bone responds to loading characteristics of Wolff’s law - where it needs to be thickened it gets thicker

Question 21

What is a strain?

Answer 21

Degree of instability is best expressed as magnitude of strain
If too low mechanical induction of tissue differentiation fails and if too high then healing progress does not progress to bone formation

Question 22

What is delayed union?

Answer 22

Failure to heal in expected time

Question 23

What causes delayed union?

Answer 23

High energy injury, distraction, instability, infection, steroids, immunosuppressant, smoking, warfarin, NSAIDs and ciprofloxacin

Question 24

What is the management for delayed healing?

Answer 24

Different fixation
Dynamization - bring fracture ends closer together
Bone grafting

Question 25

What causes non union?

Answer 25

Failure of calcification fibrocartilage
Instability - excessive osteoclasts
Abundant callus formation

Question 26

What is the symptoms and signs of non-union?

Answer 26

Pain and tenderness
Abundant callus formation
Persistent fracture line
Sclerosis - ends seal off