Unit 6b: Fracture Healing Flashcards
How does gap at the frature site affect fracture healing?
If gap is small it heals
If gap is large it does not
What are the 2 types of bone healing?
Primary and secondary
What develops around a fracture site as a bone heals naturally?
Callus
What forms the callus?
Mesenchymal (primitive =) tissue the chondroid (cartillage) then osseous (bone) tissue
Describe the process of secondary bone healing
Callus forms around fracture site - from mesenchymal (primitive) then chondroid (cartillage) then osseous (bone) tissue
Later remodelling occurs and the external callus gradually disappears as the bone regains its original strength, shape and internal architecture
What affects the time it takes for natural bone healing?
Degree of damage
Time taken to re-establish blood supply
How does the energy of the injury affect natural healing time?
Higher the energy the longer healing takes
Once a blood supply has been established how long do most long bones take to heal provided the mechanical environment is favourable?
6-12 weeks
Do metaphyseal fractures take longer or shorter to heal?
Slightly shroter
How does movement early in the healing process affect time of healing?
If movement inhibited early then fracture healing can be delayed
What is an “atrophic” or fibrous union?
When bony union does not take place due to lack of blood supply
What happens if their is excessive movement at the fracture site when healing?
Cartilage rather than bone cells are laid down
What causes an “elephant’s foot” appearance at fracture site?
When a lot of movement causes a false joint (pseudoarthrosis) to form between rapidly proliferating cartilage cells at either end
What happens in weeks 0-2 in the natural healing process?
Haematoma is invaded by macrophages in surrounding tissue
Macrophages “mop 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 fracture haematoma
Capillaries bring healing and repair cells including fibroblasts which form fibrin (scar tissue)
Capillaries also bring bone-forming osteoblasts
The surviving periosteum begins to regenerate and grow between the bone fragments
What happens in weeks 6-12 of fracture healing?
New bone tissue is laid down in the endosteal space frm the residual living bone
Eventually 2 ends are reunited as a ball of “provisional callus” (which appears as dense area on x-ray)
What happens at up to about 12 months in the natural healing process?
If circumstances are correct the provisional callues continues to form woven bone which gradually remodels to form a cortex
What happens at up to 2 years in the natural healing process?
Callus matures so that the trabecular pattern is reformed
Bone remodels to accomodate the stresses that the bone experiences in that anatomical region
What is primary bone healing?
When there is no movement between fracture fragments so the fracture heals without external callus formation so new haversian systems grow directly across the fracture gap
Which type fo fracture healing is quicker in terms of radiological disappearance of the fracture line?
Primary bone healing
Why is primary healed bone weaker than secondary?
Deprives the healing bone of the physical loading it normally bears - weakened as a result of stress shielding
What is Wolff’s law?
Bone has the ability to remodel to meet the mechanical demands placed on it
What effect does physical exercise have on the structure of bone?
Increase in bone density and thickness of cortical bone - increasing its strength and thickness
Why is there large callus cross-sectional area at the fracture site in the early stages of healing?
Structural support - increases second moment of area (compensates for the low strength and rigidity of the material of the callus)
What is the rigidity of a structure dependent on?
Material stiffnes and geometrical stiffness of the structure
What is the formula for rigidity?
R = EI
E = Young's Modulus I = second moment of area
How is rigidity maintained through the healing process?
Early = high I to compensate for low E
Late = Higher E so cross-sec area (and I) decreases
Which type of loading encourages bone union?
Loading along its long axis
What are possible factors that could explain how movement at the fracture site is percieved by bone and harnessed?
Electrical effects caused by hydroxyapatite
Hormonal factors
Electromagnetic effects produced through electron flow away from the fracture site
What is meant when hydroxyapatite is described as ‘pizeoelectric’?
It develops an electrical charge when loaded
There is some evidence of which hormone being produced at fracture sites?
Substance P
