Lecture 24: Mechanisms of Bone Healing (Exam 3) Flashcards
What is the composition of the ECM in bone
- organic & water: 35%
- Inorganic: 65%
label the following bone:
Describe primary (direct) bone healing
- Requires rigid internal fixation (less than 2% strain)
- min or no fracture gap
- Osteonal reconstruction
Describe indirect (secondary) bone healing
- Intermed callus formation
- Direct bone formation (intramembranous)
- Endochondral ossification
What is strain
- Fracture gap length
- % = change in length/original length
How much strain can granulation tissue withstand
100%
How much strain can cartilage tissue withstand
10%
How much strain can bone (osteoblasts) withstand
2%
Describe contact healing
- seen in gaps less than 300 microns
- Osteons (cutting cones) - cross the fracture plane from one fragment to the other
- 50 to 80 microns/day
Describe Gap healing
- Gap is less than 1 mm
- Blood vessels & connective tissue form
- Osteoblasts deposit perpendicular lamellar bone in the gap
- Cutting cones then can cross the transverse fracture plane
- Lamellar bone becomes longitudinally oriented
What are the requirements of direct primary healing
- Rigid fixation (to decrease inter-fragmentary strain)
- Adequate reduction (putting the pieces together stablely)
- Sufficient blood supply
What is the most common type of fracture healing
Indirect (Secondary healing)
More motion = ?
More callus
What inhibits indirect healing
Rigid stabilization
What does indirect healing require
Callus formation
What are the general phases of fracture healing in indirect healing
- Hematoma formation/inflammation
- Intramembranous bone formation
- Chondrogenesis
- Endochondral ossification
What happens during the hematoma formation/inflammation
- Release of inflammatory cells & mediators
- Bone morhogenetic protein (BMP) & other TGF-beta protiens
What growth factor is seen in endochondral ossification
Transforming Growth factor beta
List the “summarized” 4 general phases of fracture healing
- Hematoma formation (inflammation) phase
- Soft callus formation (proliferative) phase
- Hard callus formation (maturing/modeling phase)
- Remodeling phase
What type of bone healing is faster
Indirect bone healing
What needs to be understood to help avoid fracture complications
- Bone healing
- Bone blood supply
- Growth factors
- Surgical principles
Define fracture nonunion
- All evidence of osteogenic activity @ fracture site has ceased
- Union NOT possible w/out sx inervention
What are the two classifications of fracture nonunion
- Viable
- Nonviable
Define Viable-hypertrophic nonunion
- Abundant callus but NOT bridging of the fracture site
- “Elephant foot”
What causes a viable- hypertrophic nonunion
- Inadequate stabilization
- Premature weight-bearing
- Too much activity of px
Define Viable-mildly hypertrophic nonunion
- Mild callus but NOT bridging the fracture sit
- “Horses foot”
What causes a viable mildly hypertrophic nonunion
Inadequate stabilization usually due to implant failure (like plate breaks or if the screws fall out)
Define Viable-oligotrophic
- No callus - just fibrous tissue & blood vessels joining the ends
- See rounding fracture edges, resorption of bone, & shortening of fragments
What causes a viable oligotrophic
Displacement of fracture fragments or inadequately apposed fragments
Describe a nonviable dystrophic nonunion
Intermediate fragments of a fracture heal to one main fragment & not the other
What causes a non viable dystrophic nonunion
- Poor blood supply on the non-healing side
- Instability on avascular side
- Commonly seen in older animals w/ poorer blood supply
Describe nonviable-necrotic nonunion
- Fragments have no blood supply & cannot heal to any of the main fragments
- “sequestrum”
- Avascularity of fragment can lead to implant loosening
What are the causes of nonviable-necrotic nonunion
- Poor blood supply
- Infection @ the fracture site (doesn’t have to have an infection)
Describe a nonviable - defect nonunion
- Large defect - even if the ends have blood supply they cannot bridge bone
What are the causes of a nonviable- defect nonunion
Massive loss of bone @ the fracture site
What fractures are considered viable
- Hypertrophic nonunion
- Mildly hypertrophic nonunion
- Oligotrophic
What fractures are considered non viable
- Dystrophic nonunion
- Necrotic nonunion
- Defect nonunion
- Atrophic nonunion
Describe a nonviable- atrophic nonunion
- End result of other 3 of nonviable nonunions
- Uncommon
- Most difficult cases to treat
What are some causes of nonunion
- Infection
- Ischemia
- Distraction of bone ends
- Excessive compression of bone ends
- Interposition of soft tissue @ fracture
- Improper implant fixation
- Systemic factors
List some clinical signs of a nonunion
- Pain @ the fracture site
- Lameness (usually non-wt-bearing)
- Disuse atrophy of limb
- Movement felt @ fracture site
Radiographic signs of nonunion
- Fracture gap
- No activity @ fracture ends
- Obliteration of marrow cavity
- Osteopenia of surrounding bone
- Callus does not bridge the fracture gap (if present)
T/F: Even if callus is present it does not mean there is a bridge of the fracture gap
True
What are the Txs for nonunions
- Rigid stabilization of fracture
- Enhancing blood supply *bone grafting)
- Treat underlying causes of nonunion (infection, fracture caps, & ensure metabolic health)
What is a malunion
A fracture that heals in a non-anatomic position
What are causes of malunions
- Untreated fracture
- Improperly treated fracture
- Premature excessive wt-bearing on the fracture
What are some clinical results of malunion
- Angular limb deformities
- Limb shortening
- Gait abnorms
- Degenerative joint disease
What is a delayed union
Fracture not healed in expected time (can differ depending on the animal)
What supplys 80 to 85% of blood supply to the bone marrow
Nutrient artery
Define extraosseous blood supply
Supplies early periosteal callus; medullary supply eventually take back over
What is an autogenous graft transplant
Transplant w/in the same indiv
What is an allograft transplant
Transplant btw/ different indiv but same species
What is an Xenograft transplant
Bone graft transplant btw/ different individuals that are different species
What are the 4 O’s of grafting
- Osteogenesis
- Osteoconduction
- Osteoinduction
- Osteopromotion
Describe osteogenesis
Osteoblasts that survive transfer (very few survive)
Describe Osteoconduction
Graft acts as scaffold in which new bone is laid down
Describe osteoinduction
Graft induces cells to promote new bone (Bone morphogenetic protein)
Describe osteopromotion
Material that enhances regeneration of bone (platelet rich plasma)
What is the physiology of a cancellous bone graft
- The bone graft is separated from its blood supple
- few cells survive (osteogenic cells)
- Mesenchymal stem cells are induced to form bone cell lines
- Deposition new bone from osteoprogenitor cells
- Resorption of necrotic bone
What are some indications for bone grafts
- Any orthopedic fracture or arthrodesis
- Infected fractures
- Delayed/nonunions
- Bone loss - cysts/fractures
- Limb- sparing for bone tumors
What are the done site for harvesting a cancellous bone graft
- ilial wing
- Proximal tibia
- Proximal humerus
- Distal femur
