Mechanisms of Bone Healing (24)

Question 1

What are osteoprogenitor cells from?

Answer 1

directly from mesenchymal stem cells

Question 2

What is the ECM made of?

Answer 2

• organic and water: 35% - type I collagen
• inorganic 65%

Question 3

Where are osteoprogenitor cells?

Answer 3

metaphysis

Question 4

What are the types of fracture healing?

Answer 4

• direct (primary)
• indirect (secondary)

Question 5

What is direct (primary) fracture healing?

Answer 5

osteonal reconstruction - requires rigid internal fixation

minimal or no fracture gap

Question 6

How much strain can direct (primary) fracture healing have?

Answer 6

2%

Question 7

What is indirect (secondary) fracture healing?

Answer 7

intermediate callus formation - direct bone formation (intramembranous) & endochondral ossification

Question 8

What is strain?

Answer 8

fracture gap length
- change in length / original length

percentage

Question 9

Strains withstood by tissue:

Answer 9

granulation tissue: 100%
cartilage: 10%
bone: 2%

Question 10

What are the types of direct healing?

Answer 10

contact healing
gap healing

Question 11

What is direct healing - contact?

Answer 11

• gaps less than 300 microns
• osteons
• cross the fracture plane - one fragment to the other
• 50-80 microns/day

Question 12

What is direct healing - gap?

Answer 12

• gaps less than 1 mm

Question 13

Type of healing?

Answer 13

contact healing

Question 14

What is intra-cortical remodeling?

Answer 14

formation of new osteons - cutting cones

Question 15

Type of healing?

Answer 15

gap healing

Question 16

What are the requirements for direct (primary) healing?

Answer 16

1. rigid fixation
2. adequate reduction
3. sufficient blood supply

Question 17

What is indirect (secondary) healing?

Answer 17

• most common type of fracture healing
• enhanced by motion
• inhibited by rigid stabilization
• requires callus formation

Question 18

Type of fracture healing?

Answer 18

indirect (secondary) healing

Question 19

What are the 4 phases of fracture healing - indirect secondary?

Answer 19

1. hematoma formation (inflammation)
2. soft callus formation (proliferative) phase
3. hard callus formation (maturing or modeling) phase
4. remodeling phase

Question 20

What are the 4 phases of fracture healing - indirect secondary - specific?

Answer 20

1. hematoma formation/inflammation
2. intramembranous bone formation
3. chondrogenesis
4. endochondral ossification

Question 21

Type of healing?

Answer 21

indirect - soft callus

Question 22

Fracture healing type?

Answer 22

indirect - hard callus

Question 23

Direct/Indirect bone healing is a faster process

Answer 23

Indirect

Question 24

A dog broke its leg and got a bone plate in its leg. What type of healing?

Answer 24

direct fracture healing

indirect: pins/wires, interlocking nail, external fixation, locking compression plates

Question 25

What is fracture non-union?

Answer 25

all evidence of osteogenic activity at fracture site has ceased fracture union NOT possible without surgical intervention

Question 26

Type of nonunion?

Answer 26

hypertrophic - viable

Question 27

What is hypertrophic nonunion?

Answer 27

- abundant callus but NOT bridging the fracture site - "elephant foot" causes: inadequate stabilization, premature weight bearing, too much activity of patient

Question 28

Type of nonunion?

Answer 28

hypertrophic

Question 29

Nonunion type?

Answer 29

mildly hypertrophic nonunion

Question 30

What are the characteristics of mildly hypertrophic nonunion?

Answer 30

- mild callus but NOT bridging the fracture site - called the horse's foot

Question 31

What are the causes of mildy hypertrophic nonunion?

Answer 31

inadequate stabilization usually due to implant failure ex. plate breaks, screw pulls out

Question 32

Type of nonunion?

Answer 32

oligotrophic

Question 33

What are characteristics of oligotrophic viable nonunion?

Answer 33

no callus - just fibrous tissue and blood vessels joining ends see rounding of fracture edges, respiration of bone and shortening of fragments

Question 34

What are causes of oligotrophic nonunion?

Answer 34

displacement of fracture fragments or inadequately apposed fragments

Question 35

Type of nonunion?

Answer 35

dystrophic nonunion

Question 36

What are characteristics of dystrophic nonunion?

Answer 36

intermediate fragments of fracture heal to one main fragment and not the other

Question 37

What are some causes of dystrophic nonunion?

Answer 37

poor blood supply on non-healing side instability on avascular side more common in older animals with poorer blood supply

Question 38

Type of nonunion?

Answer 38

necrotic nonunion

Question 39

What are characteristics of necrotic nonunion?

Answer 39

fragments have no blood supply and cannot heal to any of main fragments sequestrum - avascularity of fragment can lead to implant loosening

Question 40

Type of nonunion?

Answer 40

defect nonunion

Question 41

What is atrophic nonunion?

Answer 41

end result of other 3 nonviable nonunions; uncommon, the most difficult cases to treat

Question 41

What is a defect nonunion and its cause?

Answer 41

large defect - even if ends have blood supply; they cannot bridge bone massive loss of bone at fracture site

Question 41

Type of nonunion?

Answer 41

atrophic nonunion

Question 42

What are nonunion causes?

Answer 42

Question 43

What are clinical signs of nonunion?

Answer 43

Question 44

What are radiographic signs of nonunion?

Answer 44

Question 45

How do you treat nonunions?

Answer 45

rigid stabilization of fracture - enhancing blood supply - treat underlying cause of nonunion

Question 46

What is a malunion?

Answer 46

fracture that heals in a non-anatomic position

Question 47

What are causes of malunions?

Answer 47

- untreated fracture - improperly treated fracture - premature excessive weight bearing on fracture

Question 48

What do malunions result in?

Answer 48

- angular limb deformities - limb shortening - gait abnormalities - degenerative joint disease

Question 49

What is a delayed union?

Answer 49

fracture not healed in expected time - considering patient and fracture environment

Question 50

What is the blood supply to the bone?

Answer 50

- 80-85% nutrient artery to bone marrow - periosteal vessels - epiphyseal and metaphyseal vessels - differences exist depending on growth versus maturity phase

Question 51

What is the blood supply after injury?

Answer 51

extraosseous - supplies early periosteal callus

Question 52

What are the types of graft transplanting?

Answer 52

autogenous, allograft, xenograft

Question 53

What are the "Os" of grafting?

Answer 53

- osteogenesis - osteoconduction - osteoinduction - osteopromotion

Question 54

What is osteogenesis - bone grafting?

Answer 54

osteoblasts that survive transfer

Question 55

What is osteoconduction - bone grafting?

Answer 55

graft acts as scaffold in which new bone is laid down

Question 55

What is osteoinduction - bone grafting?

Answer 55

graft induces cells to promote new bone - bone morphogenetic protein

Question 55

What are the bone common sites for harvesting a cancellous bone graft in a donor?*

Answer 55

ilial wing proximal tibia and humerus distal femur

Question 55

What is osteopromotion - bone grafting?

Answer 55

material that enhances regeneration of bone - platelet-rich plasma

Question 55

What is cancellous bone graft?

Answer 55

- bone graft separated from its blood supply - few cells survive - osteogenic cells - mesenchymal stem cells are induced to form bone cell lines (inductive proteins) - deposition new bone from osteoprogenitor cells - resorption of necrotic bone

Question 56

When should you get a bone graft?

Answer 56