Bone Healing And Bone Grafting Flashcards
What is the blood supply to the long bones in a mature animal?
Principle nutrient artery
Metaphyseal arteries
Periosteal arteries
What is the blood supply to the long bones in immature animals?
Epiphyseal and metaphyseal arteries
How does blood supply change in a fractured bone?
Develops extraossecous blood supply —- supplying periosteal bone proliferation
What are the stages of indirect healing (aka callus formation)?
Inflammation
Repair
Remodeling
What type of bone healing occurs with unstable mechanical environment/motion between fracture fragments
Indirect
What occurs in the inflammatory stage of indirect bone healing?
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
What occurs in the remodeling stage of indirect bone healing?
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
What is direct bone healing?
Filling of fracture site with no callus
Requires anatomical reduction and rigid fixation which minimize secondary healing phase (usually plate fixation)
Minimal interfragmentary strain
T/F: it take longer to gain mechanical strength when healing has occurred by direct bone healing rather than indirect bone healing
True
Reducing a fracture (increases/decreases) interfragmentary strain
Increases
We try to compensate for this by adding fixators
Gap healing occurs then the fracture gap is _______mm
<1
Interfragmentary strain must be <2%
What is the process of gap healing ?
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
Contact healing can only occurs if the defect between fracture sites is ______mm
<0.01
How does contact healing occur?
Lamellar bone is layer in normal axial direction
Bony union and remodeling simultaneous
Initiated by cutting cones of osteoblasts directly followed by osteoblasts
How does healing of cancellous bone occur?
Fracture gap is filled with new trabecular bone followed by the cortical shell
(Eg metaphyseal fractures)
How does healing of a physeal fracture occurs?
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
What type of healing usually occurs with bone plate fixation?
Direct healing
What type of healing occurs with external fixators?
Direct or indirect
What type of healing occurs with IM pins with wires/ cast/ splints/ no fixation
Indirect healing
Intramedulary pins/interlocking nails disrupt ________ blood supply
Endosteal/medullary
Bone plates disrupt _________ blood supply
Periosteal
Why do we use bone grafts?
Bone loss
Arthodesis
Delayed or non-union fractures
Old age
What are the disadvantages to using bone grafts?
Increased surgical time
Increased pain
Increased blood loss
Increased expense
What are the functions of bone grafts?
Osteogenesis — osteoblasts
Osteoinduction — recruitment of mesenchymal cells
Osteoconduction — scaffold
What is the gold standard for bone graphs?
Autogenous cancellous bone graft
Promotes osteogenesis and is readily available
What are the phases of cancellous grafts in healing and how long does each phase take?
Inflammation (hours)
Revascularization (1-2weeks)
Osteoconduction (2-4weeks)
Mechanical support (up to 12weeks)
How are cancellous bone grafts collected?
Drill hole through cortex (proximal humerus/ proximal tibia/ wing of ileum)
Scoop out cancellous bone with curette
Has short storage time!
What type of graft is available as frozen chips or powder and decreases surgical time?
Allograft
T/F: allograft lacks osteopenia properties
True
What sites can you get a cortical bone graft from?
Rib, ulna, fibula, ililal wing
T/F: cortical bone has more osteogenic properties than osteoconductive
False
Cortical bone — osteoconductive
What are the phases of healing witha cortical bone graft?
Osteoclasts move into graft and resort bone
Osteoblasts follow and lay down new bone
Mechanical strength of graft is maintained “creeping substitution”
Why type of bone graft provides immediate mechanical support and promotes osteogenesis, osteoindcutive, and osteoconductive function?
Cortical-cancellous bone graft
— usually autogenous
