Fracture healing

Question 1

How does the fracture gap size affect bone healing?

Answer 1

If gap is small it heals

If gap is large it does not

Question 2

What are the 2 types of bone healing?

Answer 2

Primary

Secondary (natural)

Question 3

Briefly describe secondary bone healing

Answer 3

Callous forms of:

Mesenchymal (primitive) 
then 
Chondroid (cartilage) 
then 
Osseous (bone)

Question 4

What determines the time scale of natural bone healing?

Answer 4

Time taken for a new blood supply to be re-stablished (higher the energy usually longer)

Question 5

Once a blood supply has been established roughly how long do most long bone fractures take to heal?

Answer 5

6-12 weeks

Question 6

Once a blood supply has been established do metaphyseal (cancellous bone) fractures take longer or shorter than long bone fractures to heal?

Answer 6

Shorter than long bones

Question 7

What can cause “atrophic” or fibrous union?

Answer 7

No blood supply re-established

Excessive movement at fracture site

Question 8

What happens when there is excessive movement at the fracture site?

Answer 8

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

Question 9

What is an “elephant’s foot” appearance?

Answer 9

If there is a lot of movement at fracture site - false joint (pseudoarthrosis) forms between cartillage cells at either end

Question 10

What happens in weeks 0-2 of the natural healing process?

Answer 10

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

Question 11

What happens in weeks 2-6 of the natural healing process?

Answer 11

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

Question 12

What happens in weeks 6-12 in the natural healing process?

Answer 12

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

Question 13

What happens in the natural healing process up to about 12 months?

Answer 13

If circumstances are correct callus continues to form woven bone which gradually remodels to form a cortex

Question 14

What happens in the natural healing process up to 2 years?

Answer 14

Callus matures so that the trabecular pattern is reformed

Bone remodels to accommodate the stresses that bone experiences in that anatomical region

Question 15

When does primary bone healing occur?

Answer 15

When there is no relative movement (or micromovement) between fracture fragments during the healing process

Question 16

Describe primary bone healing

Answer 16

When there is no movemnt at fracture site
Fracture heals without external callus
New Haversian systems grow directly across fracture gap

Question 17

How do primary and secondary bone healing differ radiologically?

Answer 17

Quicker healing process by primary in terms of the radiological disappearance of the fracture line

Question 18

Why does primary bone healing happen and why is it bad?

Answer 18

Rigid fixation - deprives healing bone of physical loading it normally bears
Bone is additionally weakened by this stress shielding

Question 19

Describe Wolff’s law

Answer 19

Bone has the ability to remodel by altering its size, shape and structure to meet the mechanical demands placed on it

Question 20

What effect does physical exercise have on bone?

Answer 20

Increase in bone density

Increased thickness of cortical bone

Question 21

How does bone maintain its strength at the early stages of fracture healing?

Answer 21

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

Question 22

Equation for calculating rigidity

Answer 22

R = EI

Question 23

What type of movement is beneficial for bone healing?

Answer 23

Loading along long axis

Question 24

Give 3 possible explanations for how movement at the fracture site is percieved by the body

Answer 24

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

Question 25

Hydroxyapatite is piesoelectric - what does this mean?

Answer 25

It develops an electrical charge when loaded