Fracture Healing Flashcards
What type of CT is bone?
Bone is is a specialised form of dense connective tissue
List 3 mechanical functions of bone
- skeleton rigidity
- function as attachment and lever for muscle
- supports the body against gravity
What is the chemical function of bone
Calcium homeostasis and metabolism
What is the haematological function of bone
Bone marrow manufactures stem cells and other substances, which in turn produce RBCs
Compare and contrast the 3 macroscopic types of bone
- Trabecular (cancellous/spongy) bone ➞ sponge like network
* located at ends of long bones - Compact (cortical) bone ➞ strong , dense bone
- no spaces/hollows in bone matrix visible to the eye
- stiffer but more brittle than cancellous bone, withstands less strain before failure
- Woven bone ➞ Immature, disorganised bone
- absent from normal bone after age 4
- seen in fracture callus in both children and adults
Compare and constrast the 3 types of bone cells
- Osteoblasts
- formation, organization and mineralisation of bone ECM
- synthesis of collagen and other bone proteins
- Osteocytes ➞ similar to nerve cells
- regulates response of bone to mechanical environment
- Intercellular communication via canaliculi
- Osteoclasts
- responsible for resorption of bone matrix (osteoid)
- large motile, multinucleated cell
Describe the constituents of bone
Organic component (40% dry weight of bone)
- Collagen (90%)
- Proteoglycans
- Matrix Proteins
- Cells
Inorganic component (60% dry weight of bone)
- Calcium Hydroxyapatite
- Osteocalcium Phosphate
What component of bone provides compressive strength?
Calcium Hydroxyapatite (Inorganic component)
List the 4 sources of blood supply to bone AND where each supplies
- Nutrient artery system ➞ inner 2/3 of cortex from within (endosteal)
- Periosteal system ➞ outer 1/3 of cortex
- Metaphyseal system ➞ ‘zone of provisional calcification’ in physis
- Epiphyseal system ➞ supplies physis by diffusion

Vessels from which system contribute to endochondral ossification in children?
Nutrient artery system - in the child, these vessels end on metaphyseal side of the physis and contribute to endochondral ossification
The Metaphyseal system anastomoses with which other system?
The nutrient artery system
Which system supplies blood to the femoral and radial heads?
Epiphyseal system
Why is blood supply to the femoral and radial heads tenuous?
Femoral and radial heads are almost entirely covered by cartilage
Vessels from the from epiphyseal system enter in region between articular cartilage and growth-plate cartilage
Hence, blood supply is tenuous
List the 3 stages of fracture healing
- Inflammatory response
- Reparative response
- Remodelling
What occurs during the Inflammatory response of fracture healing (Incl timeframe)|
Time of injury to 24-72 hours
- Injured tissues + platelets release vasoactive mediators, growth factors and other cytokines
- These cytokines influence cell migration, proliferation, differentiation and matrix synthesis
- growth factors recruit fibroblasts, mesenchymal cells and osteoprogenitor cells to fracture site
- Macrophages, PMNs and mast cells (48hr) arrive at fracture site to begin process of removing the tissue debris
What occurs during the reparative response of fracture healing (Incl timeframe)|
2 days to 2 weeks
- vasoactive substances cause neovascularisation and local vasodilation
- undifferentiated mesenchymal cells migrate to fracture site and form cells which in turn form cartilage, bone or fibrous tissue
- the fracture haematoma is organised, fibroblasts and chondroblasts appear between bone ends and cartilage is formed
What occurs during Remodelling of fracture healing (Incl timeframe)
Middle of repair phase up to 7 years (most occurs in 1st year)
- osteoclasts resorb bone and the resulting hole is filled by osteoblasts with new bone and osteocytes
- fracture healing is complete when there is repopulation of the medullary canal
What is remodelling of woven bone dependant on?
What ‘law’ does this follow
Remodelling of the woven bone is dependent on the mechanical forces applied to it
Wolff’s Law - ‘form follows function’
List 4 local and 4 systemic factors which affect fracture healing

The amount of callus formed is _________ to the amount of immobilisation of the fracture
What does this mean for fractures fixed with rigid compression plates?
inversely proportional
fractures fixed with rigid compression plates permits almost no movement resulting in primary bone healing with little or no visible callus formation
Bone is viscoelastic, what does this mean?
time dependent property where the deformation of the material is related to the rate of loading
Bone is anisotropic, what does this mean?
Different mechanical properties when loaded along different axes
This is because the structure of bone is dissimilar in the transverse and longitudinal directions
Ie. cortical bone is stronger in compression than tension and weakest in shear
When a tension force is applied to bone, what fracture results?
Explain the mechanics of this AND state the most common locations this occurs in
Transverse fracture
Failure due to debonding at the cement lines and pulling out of the osteons
Tends to occur in areas with a large proportion of cancellous bone eg. calcaneum, 5th metatarsal

When a compression force is applied to bone, what fracture results?
Explain the mechanics of this AND state the most common locations this occurs in
Oblique fracture at 30o angle (b/c shear forces at this angle are responsible for the failure)
Failure due to oblique cracking of the osteons (few fractures occur purely due to compression)
Fractures tend to occur in the metaphyses of bones where there is more cancellous bone which is weaker



