Mechanisms of Bone Healing (24) Flashcards
Dr. Gilley
What are osteoprogenitor cells from?
directly from mesenchymal stem cells
What is the ECM made of?
- organic and water: 35% - type I collagen
- inorganic 65%
Where are osteoprogenitor cells?
metaphysis
What are the types of fracture healing?
- direct (primary)
- indirect (secondary)
What is direct (primary) fracture healing?
osteonal reconstruction - requires rigid internal fixation
minimal or no fracture gap
How much strain can direct (primary) fracture healing have?
2%
What is indirect (secondary) fracture healing?
intermediate callus formation - direct bone formation (intramembranous) & endochondral ossification
What is strain?
fracture gap length
- change in length / original length
percentage
Strains withstood by tissue:
granulation tissue: 100%
cartilage: 10%
bone: 2%
What are the types of direct healing?
contact healing
gap healing
What is direct healing - contact?
- gaps less than 300 microns
- osteons
- cross the fracture plane - one fragment to the other
- 50-80 microns/day
What is direct healing - gap?
- gaps less than 1 mm
Type of healing?
contact healing
What is intra-cortical remodeling?
formation of new osteons - cutting cones
Type of healing?
gap healing
What are the requirements for direct (primary) healing?
- rigid fixation
- adequate reduction
- sufficient blood supply
What is indirect (secondary) healing?
- most common type of fracture healing
- enhanced by motion
- inhibited by rigid stabilization
- requires callus formation
Type of fracture healing?
indirect (secondary) healing
What are the 4 phases of fracture healing - indirect secondary?
- hematoma formation (inflammation)
- soft callus formation (proliferative) phase
- hard callus formation (maturing or modeling) phase
- remodeling phase
What are the 4 phases of fracture healing - indirect secondary - specific?
- hematoma formation/inflammation
- intramembranous bone formation
- chondrogenesis
- endochondral ossification
Type of healing?
indirect - soft callus
Fracture healing type?
indirect - hard callus
Direct/Indirect bone healing is a faster process
Indirect
A dog broke its leg and got a bone plate in its leg. What type of healing?
direct fracture healing
indirect: pins/wires, interlocking nail, external fixation, locking compression plates
What is fracture non-union?
all evidence of osteogenic activity at fracture site has ceased
fracture union NOT possible without surgical intervention
Type of nonunion?
hypertrophic - viable
What is hypertrophic nonunion?
- abundant callus but NOT bridging the fracture site
- “elephant foot”
causes: inadequate stabilization, premature weight bearing, too much activity of patient
Type of nonunion?
hypertrophic
Nonunion type?
mildly hypertrophic nonunion
What are the characteristics of mildly hypertrophic nonunion?
- mild callus but NOT bridging the fracture site
- called the horse’s foot
What are the causes of mildy hypertrophic nonunion?
inadequate stabilization usually due to implant failure
ex. plate breaks, screw pulls out
Type of nonunion?
oligotrophic
What are characteristics of oligotrophic viable nonunion?
no callus - just fibrous tissue and blood vessels joining ends
see rounding of fracture edges, respiration of bone and shortening of fragments
What are causes of oligotrophic nonunion?
displacement of fracture fragments or inadequately apposed fragments
Type of nonunion?
dystrophic nonunion
What are characteristics of dystrophic nonunion?
intermediate fragments of fracture heal to one main fragment and not the other
What are some causes of dystrophic nonunion?
poor blood supply on non-healing side
instability on avascular side
more common in older animals with poorer blood supply
Type of nonunion?
necrotic nonunion
What are characteristics of necrotic nonunion?
fragments have no blood supply and cannot heal to any of main fragments
sequestrum - avascularity of fragment can lead to implant loosening
Type of nonunion?
defect nonunion
What is atrophic nonunion?
end result of other 3 nonviable nonunions; uncommon, the most difficult cases to treat
What is a defect nonunion and its cause?
large defect - even if ends have blood supply; they cannot bridge bone
massive loss of bone at fracture site
Type of nonunion?
atrophic nonunion
What are nonunion causes?
What are clinical signs of nonunion?
What are radiographic signs of nonunion?
How do you treat nonunions?
rigid stabilization of fracture
- enhancing blood supply
- treat underlying cause of nonunion
What is a malunion?
fracture that heals in a non-anatomic position
What are causes of malunions?
- untreated fracture
- improperly treated fracture
- premature excessive weight bearing on fracture
What do malunions result in?
- angular limb deformities
- limb shortening
- gait abnormalities
- degenerative joint disease
What is a delayed union?
fracture not healed in expected time
- considering patient and fracture environment
What is the blood supply to the bone?
- 80-85% nutrient artery to bone marrow
- periosteal vessels
- epiphyseal and metaphyseal vessels
- differences exist depending on growth versus maturity phase
What is the blood supply after injury?
extraosseous - supplies early periosteal callus
What are the types of graft transplanting?
autogenous, allograft, xenograft
What are the “Os” of grafting?
- osteogenesis
- osteoconduction
- osteoinduction
- osteopromotion
What is osteogenesis - bone grafting?
osteoblasts that survive transfer
What is osteoconduction - bone grafting?
graft acts as scaffold in which new bone is laid down
What is osteoinduction - bone grafting?
graft induces cells to promote new bone
- bone morphogenetic protein
What are the bone common sites for harvesting a cancellous bone graft in a donor?*
ilial wing
proximal tibia and humerus
distal femur
What is osteopromotion - bone grafting?
material that enhances regeneration of bone
- platelet-rich plasma
What is cancellous bone graft?
- 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
When should you get a bone graft?
