Unit 6b: Fracture Healing

Question 1

How does gap at the frature site affect fracture 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 and secondary

Question 3

What develops around a fracture site as a bone heals naturally?

Answer 3

Callus

Question 4

What forms the callus?

Answer 4

Mesenchymal (primitive =) tissue the chondroid (cartillage) then osseous (bone) tissue

Question 5

Describe the process of secondary bone healing

Answer 5

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

Question 6

What affects the time it takes for natural bone healing?

Answer 6

Degree of damage

Time taken to re-establish blood supply

Question 7

How does the energy of the injury affect natural healing time?

Answer 7

Higher the energy the longer healing takes

Question 8

Once a blood supply has been established how long do most long bones take to heal provided the mechanical environment is favourable?

Answer 8

6-12 weeks

Question 9

Do metaphyseal fractures take longer or shorter to heal?

Answer 9

Slightly shroter

Question 10

How does movement early in the healing process affect time of healing?

Answer 10

If movement inhibited early then fracture healing can be delayed

Question 11

What is an “atrophic” or fibrous union?

Answer 11

When bony union does not take place due to lack of blood supply

Question 12

What happens if their is excessive movement at the fracture site when healing?

Answer 12

Cartilage rather than bone cells are laid down

Question 13

What causes an “elephant’s foot” appearance at fracture site?

Answer 13

When a lot of movement causes a false joint (pseudoarthrosis) to form between rapidly proliferating cartilage cells at either end

Question 14

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

Answer 14

Haematoma is invaded by macrophages in surrounding tissue

Macrophages “mop up” dead and damaged tissue

Haematoma and dead cells are absorbed into the macrophages

Question 15

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

Answer 15

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

Question 16

What happens in weeks 6-12 of fracture healing?

Answer 16

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)

Question 17

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

Answer 17

If circumstances are correct the provisional callues continues to form woven bone which gradually remodels to form a cortex

Question 18

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

Answer 18

Callus matures so that the trabecular pattern is reformed

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

Question 19

What is primary bone healing?

Answer 19

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

Question 20

Which type fo fracture healing is quicker in terms of radiological disappearance of the fracture line?

Answer 20

Primary bone healing

Question 21

Why is primary healed bone weaker than secondary?

Answer 21

Deprives the healing bone of the physical loading it normally bears - weakened as a result of stress shielding

Question 22

What is Wolff’s law?

Answer 22

Bone has the ability to remodel to meet the mechanical demands placed on it

Question 23

What effect does physical exercise have on the structure of bone?

Answer 23

Increase in bone density and thickness of cortical bone - increasing its strength and thickness

Question 24

Why is there large callus cross-sectional area at the fracture site in the early stages of healing?

Answer 24

Structural support - increases second moment of area (compensates for the low strength and rigidity of the material of the callus)

Question 25

What is the rigidity of a structure dependent on?

Answer 25

Material stiffnes and geometrical stiffness of the structure

Question 26

What is the formula for rigidity?

Answer 26

R = EI

E = Young's Modulus 
I = second moment of area

Question 27

How is rigidity maintained through the healing process?

Answer 27

Early = high I to compensate for low E

Late = Higher E so cross-sec area (and I) decreases

Question 28

Which type of loading encourages bone union?

Answer 28

Loading along its long axis

Question 29

What are possible factors that could explain how movement at the fracture site is percieved by bone and harnessed?

Answer 29

Electrical effects caused by hydroxyapatite

Hormonal factors

Electromagnetic effects produced through electron flow away from the fracture site

Question 30

What is meant when hydroxyapatite is described as ‘pizeoelectric’?

Answer 30

It develops an electrical charge when loaded

Question 31

There is some evidence of which hormone being produced at fracture sites?

Answer 31

Substance P