Fracture healing Flashcards
How does the fracture gap size affect bone healing?
If gap is small it heals
If gap is large it does not
What are the 2 types of bone healing?
Primary
Secondary (natural)
Briefly describe secondary bone healing
Callous forms of:
Mesenchymal (primitive) then Chondroid (cartilage) then Osseous (bone)
What determines the time scale of natural bone healing?
Time taken for a new blood supply to be re-stablished (higher the energy usually longer)
Once a blood supply has been established roughly how long do most long bone fractures take to heal?
6-12 weeks
Once a blood supply has been established do metaphyseal (cancellous bone) fractures take longer or shorter than long bone fractures to heal?
Shorter than long bones
What can cause “atrophic” or fibrous union?
No blood supply re-established
Excessive movement at fracture site
What happens when there is excessive movement at the fracture site?
Cartillage rather than bone is laid down
If there is a lot of movenet a false joint (pseudoarthrosis) may form between rapidly proliferating cartilage cells at either end
What is an “elephant’s foot” appearance?
If there is a lot of movement at fracture site - false joint (pseudoarthrosis) forms between cartillage cells at either end
What happens in weeks 0-2 of the natural healing process?
Haematoma is invaded by macrophages in surrounding tissue
Reponsible for “mopping up” dead and damaged tissue
Haematoma and dead cells are absorbed into the macrophages
What happens in weeks 2-6 of the natural healing process?
New capillaries grow into the fracture haematoma
Capillaries bring healing and repair cells
Inc. fibroblasts which form fibrin (scar tissue)
Capillaries also bring bone forming osteoblasts
Surviving periosteum begins to regenerate and grow between the bone fragments
What happens in weeks 6-12 in the natural healing process?
New bone tissue is laid down in the endosteal space from the residual living bone
Eventually 2 ends are reunited as a ball of “provisional callus” - appears as dense area on an x-ray
What happens in the natural healing process up to about 12 months?
If circumstances are correct callus continues to form woven bone which gradually remodels to form a cortex
What happens in the natural healing process up to 2 years?
Callus matures so that the trabecular pattern is reformed
Bone remodels to accommodate the stresses that bone experiences in that anatomical region
When does primary bone healing occur?
When there is no relative movement (or micromovement) between fracture fragments during the healing process
Describe primary bone healing
When there is no movemnt at fracture site
Fracture heals without external callus
New Haversian systems grow directly across fracture gap
How do primary and secondary bone healing differ radiologically?
Quicker healing process by primary in terms of the radiological disappearance of the fracture line
Why does primary bone healing happen and why is it bad?
Rigid fixation - deprives healing bone of physical loading it normally bears
Bone is additionally weakened by this stress shielding
Describe Wolff’s law
Bone has the ability to remodel by altering its size, shape and structure to meet the mechanical demands placed on it
What effect does physical exercise have on bone?
Increase in bone density
Increased thickness of cortical bone
How does bone maintain its strength at the early stages of fracture healing?
Large callus cross-sec area significantly increases its second moment of area (compensates for the lower strength and rigidity of the material of the callus) - R = EI
Equation for calculating rigidity
R = EI
What type of movement is beneficial for bone healing?
Loading along long axis
Give 3 possible explanations for how movement at the fracture site is percieved by the body
Electrical effects caused by moving crystals of hydroxyapatite
Hormonal factors (some evidence of “Substance P” being produced at fracture sites
Electro-magnetic effects produced through electron flow away from the racture site
Hydroxyapatite is piesoelectric - what does this mean?
It develops an electrical charge when loaded
