Lecture 5: Bone Regeneration and Repair (Wronski)

Question 1

primary bone healing*

Answer 1

direct bone healing that doesn’t require callus formation. Only occurs when optimal fixation and stabilization can be achieved

Question 2

healing by callus formation*

Answer 2

indirect bone healing that requires an intermediate fibrocartilagenous callus

Question 3

3 main steps of primary (direct) bone healing*

Answer 3

1) Osteoclasts form resoption cavities that cross the gap between bone fragments
2) cavities filled with new bone deposited by osteoblasts
3) osteons bridge the gap between bone fragments

Question 4

4 stages of healing by callus formation (indirect bone healing)*

Answer 4

1) blood clot and inflammation. macrophages remove dead tissue, osteoclasts remove dead bone
2) soft callus formation
3) hard callus formation
4) bone modeling/remodeling

Question 5

what is the soft callus composed of?*

Answer 5

fibrous tissue and cartilage

Question 6

hard callus is composed of:*

Answer 6

woven bone (aka trebecular/spongy bone)

Question 7

how does bone modeling change composition of the hard callus in indirect bone healing?*

Answer 7

replaces woven bone with lamellar (aka cortical) bone, which is more structurally strong

Question 8

on which surface(s) of the bone does hard callous form?*

Answer 8

periosteal and endocortical/endosteal surfaces. The EXTERNAL callus forms on the periosteal surface, and the INTERNAL callus forms on the endocortical surface.

Question 9

What do the external and internal hard calluses form?*

Answer 9

external: cartilage and bone
internal: bone only

Question 10

describe the process of ossification in indirect bone healing*

Answer 10

1) initial bone formation is via intramembranous ossification on the periphery; cartilage (fibrous or hyaline) forms in the middle.
2) endochondral ossification occurs along the edge of the hyaline cartilage (hypertrophic chondrocyes and calcified cartilage form along the edges, then new bone is laid down on top of the calcified cartilage)

Question 11

what types of ossification occur in indirect bone healing?*

Answer 11

intramembranous and endochondral

Question 12

2 methods of bone fracture management*

Answer 12

1) fixation

2) stabilization

Question 13

fixation = *

Answer 13

apposition of bone fragments

Question 14

stabilization = *

Answer 14

to prevent movement of bone fragments

Question 15

factors that impair bone fracture healing (6)*

Answer 15

1) advanced age
2) poor nutritional status (i.e. low Ca)
3) inadequate blood supply
4) soft tissue b/w fractured ends of bone
5) inadequate immobilization
6) infection at fracture site

Question 16

2 types of nonunions in bone*

Answer 16

vascular and avascular (atrophic)

Question 17

vascular nonunion*

Answer 17

callus forms, but fracture fails to heal

Question 18

avascular (atrophic) nonunion*

Answer 18

lack of callus formation due to lack of adequate blood supply. a more serious condition than vascular nonunion

Question 19

typical site of avascular nonunion. Why?*

Answer 19

distal tibia. This site naturally has poor blood supply

Question 20

6 methods of stimulating bone fracture healing*

Answer 20

1) implantation of cancellous bone autograft (most common method)
2) percutaneous injection of bone marrow cells
3) implantation of bone graft substitute (i.e. ceramic material)
4) bone morphogenetic protein (BMP) (a gel applied to site of fracture)
5) electrical or ultrasound stimulation
6) shock wave treatment

Question 21

how does shock wave treatment stimulate bone fracture healing?*

Answer 21

induces small cracks at site of fracture to stimulate bone growth and increase vascularization

Question 22

autograft vs. allograft vs. xenograft*

Answer 22

allograft = taking bone graft from a different individual of the same species and implanting it at the site of nonunion
autograft = taking and implanting from/to SAME individual
xenograft = taking from one species and implanting to another species

Question 23

4 sources of arterial blood supply to long bones*

Answer 23

1) nutrient artery (marrow cavity)
2) metaphyseal artery
3) epiphyseal artery (penetrate cortical bone)
4) periosteal artery (along periosteal surface)

Question 24

epiphyseal plate =*

Answer 24

growth plate

Question 25

why do fractures in diaphysis heal slower than fractures in metaphysis or epiphysis? **

Answer 25

metaphysis and epiphysis have better blood supply than diaphysis

Question 26

Can blood from metaphysis diffuse into the growth plate of a bone and allow for normal growth if there is an injury to the growth plate? ***

Answer 26

No. The zone of calcified cartilage at the ase of the growth plate blocks nutrients from metaphysis from getting to zone of proliferating cartilage.

Question 27

in which direction do centripetal and centrifugal blood flow?*

Answer 27

centripetal = inward
centrifugal = outward

Question 28

blood flow to cortical bone in sites of heavy vs. loose periosteal attachments*

Answer 28

heavy: outer third of cortex supplied by centripetal flow of periosteal aa., inner two-thirds supplied by centrifugal flow of nutrient a.
loose: whole cortex supplied by centrifugal flow from nutrient artery

Question 29

why do the ends of bone die after a fracture?

Answer 29

blood supply to osteocytes is interrupted due to damaged haversian canals

Question 30

modeling of the callus during indirect bone healing consists of:

Answer 30

removing the “hump” of the callus by osteoclastic activity to restore bone to its normal pre-fracture contour

Question 31

How does differentiation of progenitor cells in callus formation vary with vascularization of the tissue?

Answer 31

those furthest away from blood supply differentiate into chondroblasts; those closer to blood supply differentiate into osteoblasts.

Question 32

Role of intramembranous vs. endochondral ossification in fracture healing

Answer 32

intramembranous ossification includes formation of bone matrix by osteoblasts, and formation of cartilage by chondroblasts. Endochondral ossification replaces the cartilage with compact cortical bone.

Question 33

most common reason for poor fracture healing in animals

Answer 33

inadequate fixation

Question 34

most common method to resolve avascular nonunion

Answer 34

placement of a cancellous bone autograft or a percutaneous injection of bone marrow cells at the site of nonunion, which introduces cells with osteogenic potential for the stimulation of fracture healing

Question 35

most common method for treating nonunions in general*

Answer 35

rigid internal fixation in combination with implantation of a cancellous bone autograft

Question 36

what does the metaphyseal a. supply in bone?*

Answer 36

ossifying trebeculae

Question 37

what do the epiphyseal capillaries supply?*

Answer 37

proliferating chondrocytes