Bone Healing And Bone Grafting

Question 1

What is the blood supply to the long bones in a mature animal?

Answer 1

Principle nutrient artery
Metaphyseal arteries
Periosteal arteries

Question 2

What is the blood supply to the long bones in immature animals?

Answer 2

Epiphyseal and metaphyseal arteries

Question 3

How does blood supply change in a fractured bone?

Answer 3

Develops extraossecous blood supply —- supplying periosteal bone proliferation

Question 4

What are the stages of indirect healing (aka callus formation)?

Answer 4

Inflammation
Repair
Remodeling

Question 5

What type of bone healing occurs with unstable mechanical environment/motion between fracture fragments

Answer 5

Indirect

Question 6

What occurs in the inflammatory stage of indirect bone healing?

Answer 6

From time of fracture, lasting 3-4days

Clot at fracture site
-osteoinductive growth factors causing angiogenesis and bone formation

-abundant mast cells with vasoactive substances

Question 7

What occurs in the remodeling stage of indirect bone healing?

Answer 7

Takes about 2 months

Clot differentiates into granulation tissue

Gain in strength - soft callus

Mesenchymal cells become osteoblasts
-lay down fibrocartilage

Mineralizes forming a hard callus
-bony union

Question 8

What is direct bone healing?

Answer 8

Filling of fracture site with no callus

Requires anatomical reduction and rigid fixation which minimize secondary healing phase (usually plate fixation)

Minimal interfragmentary strain

Question 9

T/F: it take longer to gain mechanical strength when healing has occurred by direct bone healing rather than indirect bone healing

Answer 9

True

Question 10

Reducing a fracture (increases/decreases) interfragmentary strain

Answer 10

Increases

We try to compensate for this by adding fixators

Question 11

Gap healing occurs then the fracture gap is _______mm

Answer 11

<1

Interfragmentary strain must be <2%

Question 12

What is the process of gap healing ?

Answer 12

Osteoblasts deposit lamina bone in fracture gap perpendicular to long axis

Mechanically week at fracture ends

Osteoclasts form cutting cones along osteoblasts to lay longitudinally oriented lamellar bone

Question 13

Contact healing can only occurs if the defect between fracture sites is ______mm

Answer 13

<0.01

Question 14

How does contact healing occur?

Answer 14

Lamellar bone is layer in normal axial direction

Bony union and remodeling simultaneous

Initiated by cutting cones of osteoblasts directly followed by osteoblasts

Question 15

How does healing of cancellous bone occur?

Answer 15

Fracture gap is filled with new trabecular bone followed by the cortical shell

(Eg metaphyseal fractures)

Question 16

How does healing of a physeal fracture occurs?

Answer 16

Fractures occur in this area because it is weaker than surrounding bone

Fracture of zone of hypertrophy will heal by continued growth of physeal cartilage

Fracture of zone of proliferation will heal by endochondrial ossification —> prevent normal physeal function and premature physeal closure

Question 17

What type of healing usually occurs with bone plate fixation?

Answer 17

Direct healing

Question 18

What type of healing occurs with external fixators?

Answer 18

Direct or indirect

Question 19

What type of healing occurs with IM pins with wires/ cast/ splints/ no fixation

Answer 19

Indirect healing

Question 20

Intramedulary pins/interlocking nails disrupt ________ blood supply

Answer 20

Endosteal/medullary

Question 21

Bone plates disrupt _________ blood supply

Answer 21

Periosteal

Question 22

Why do we use bone grafts?

Answer 22

Bone loss
Arthodesis
Delayed or non-union fractures
Old age

Question 23

What are the disadvantages to using bone grafts?

Answer 23

Increased surgical time
Increased pain
Increased blood loss
Increased expense

Question 24

What are the functions of bone grafts?

Answer 24

Osteogenesis — osteoblasts

Osteoinduction — recruitment of mesenchymal cells

Osteoconduction — scaffold

Question 25

What is the gold standard for bone graphs?

Answer 25

Autogenous cancellous bone graft

Promotes osteogenesis and is readily available

Question 26

What are the phases of cancellous grafts in healing and how long does each phase take?

Answer 26

Inflammation (hours)

Revascularization (1-2weeks)

Osteoconduction (2-4weeks)

Mechanical support (up to 12weeks)

Question 27

How are cancellous bone grafts collected?

Answer 27

Drill hole through cortex (proximal humerus/ proximal tibia/ wing of ileum)

Scoop out cancellous bone with curette

Has short storage time!

Question 28

What type of graft is available as frozen chips or powder and decreases surgical time?

Answer 28

Allograft

Question 29

T/F: allograft lacks osteopenia properties

Answer 29

True

Question 30

What sites can you get a cortical bone graft from?

Answer 30

Rib, ulna, fibula, ililal wing

Question 31

T/F: cortical bone has more osteogenic properties than osteoconductive

Answer 31

False

Cortical bone — osteoconductive

Question 32

What are the phases of healing witha cortical bone graft?

Answer 32

Osteoclasts move into graft and resort bone

Osteoblasts follow and lay down new bone

Mechanical strength of graft is maintained “creeping substitution”

Question 33

Why type of bone graft provides immediate mechanical support and promotes osteogenesis, osteoindcutive, and osteoconductive function?

Answer 33

Cortical-cancellous bone graft

— usually autogenous