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”