Lecture 5: Bone Regeneration and Repair (Wronski) Flashcards
primary bone healing*
direct bone healing that doesn’t require callus formation. Only occurs when optimal fixation and stabilization can be achieved
healing by callus formation*
indirect bone healing that requires an intermediate fibrocartilagenous callus
3 main steps of primary (direct) bone healing*
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
4 stages of healing by callus formation (indirect bone healing)*
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
what is the soft callus composed of?*
fibrous tissue and cartilage
hard callus is composed of:*
woven bone (aka trebecular/spongy bone)
how does bone modeling change composition of the hard callus in indirect bone healing?*
replaces woven bone with lamellar (aka cortical) bone, which is more structurally strong
on which surface(s) of the bone does hard callous form?*
periosteal and endocortical/endosteal surfaces. The EXTERNAL callus forms on the periosteal surface, and the INTERNAL callus forms on the endocortical surface.
What do the external and internal hard calluses form?*
external: cartilage and bone
internal: bone only
describe the process of ossification in indirect bone healing*
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)
what types of ossification occur in indirect bone healing?*
intramembranous and endochondral
2 methods of bone fracture management*
1) fixation
2) stabilization
fixation = *
apposition of bone fragments
stabilization = *
to prevent movement of bone fragments
factors that impair bone fracture healing (6)*
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
2 types of nonunions in bone*
vascular and avascular (atrophic)
vascular nonunion*
callus forms, but fracture fails to heal
avascular (atrophic) nonunion*
lack of callus formation due to lack of adequate blood supply. a more serious condition than vascular nonunion
typical site of avascular nonunion. Why?*
distal tibia. This site naturally has poor blood supply
6 methods of stimulating bone fracture healing*
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
how does shock wave treatment stimulate bone fracture healing?*
induces small cracks at site of fracture to stimulate bone growth and increase vascularization
autograft vs. allograft vs. xenograft*
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
4 sources of arterial blood supply to long bones*
1) nutrient artery (marrow cavity)
2) metaphyseal artery
3) epiphyseal artery (penetrate cortical bone)
4) periosteal artery (along periosteal surface)
epiphyseal plate =*
growth plate
why do fractures in diaphysis heal slower than fractures in metaphysis or epiphysis? **
metaphysis and epiphysis have better blood supply than diaphysis
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? ***
No. The zone of calcified cartilage at the ase of the growth plate blocks nutrients from metaphysis from getting to zone of proliferating cartilage.
in which direction do centripetal and centrifugal blood flow?*
centripetal = inward centrifugal = outward
blood flow to cortical bone in sites of heavy vs. loose periosteal attachments*
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
why do the ends of bone die after a fracture?
blood supply to osteocytes is interrupted due to damaged haversian canals
modeling of the callus during indirect bone healing consists of:
removing the “hump” of the callus by osteoclastic activity to restore bone to its normal pre-fracture contour
How does differentiation of progenitor cells in callus formation vary with vascularization of the tissue?
those furthest away from blood supply differentiate into chondroblasts; those closer to blood supply differentiate into osteoblasts.
Role of intramembranous vs. endochondral ossification in fracture healing
intramembranous ossification includes formation of bone matrix by osteoblasts, and formation of cartilage by chondroblasts. Endochondral ossification replaces the cartilage with compact cortical bone.
most common reason for poor fracture healing in animals
inadequate fixation
most common method to resolve avascular nonunion
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
most common method for treating nonunions in general*
rigid internal fixation in combination with implantation of a cancellous bone autograft
what does the metaphyseal a. supply in bone?*
ossifying trebeculae
what do the epiphyseal capillaries supply?*
proliferating chondrocytes
