Unit 6a: Fractures, fracture healing & non-surgical fixation

Question 1

What are the most important mechanical properties of bone?

Answer 1

strength and stiffness

Question 2

Which type of loading is a long bone most resistant under?

Answer 2

best resistance to compression, then tension, and is weakest in shear.

Question 3

What determines the location and type of fracture?

Answer 3

1. geometry + structure of the bone
2. type of loading (eg. tension, compression, shear)…
3. rate of loading

Question 4

Under an axial load, what is the stiffness of the bone proportional to?

Answer 4

its cross sectional area

Question 5

Under a bending load, which two factors affect stiffness of a bone? what term describes this?

Answer 5

cross sectional area and the distribution of bone around a neutral axis

= second moment of area

Question 6

Under a torsional load, which two factors affect stiffness of a bone? what term describes this?

Answer 6

cross sectional area and the distribution of bone around a neutral axis

= polar second moment of area

Question 7

How does the geometry of the tibia affect fracture location when subjected to a torsional load?

Answer 7

fracture occurs distally

because distally there is more bone located close to the neutral axis so the polar second moment of area is low

whereas proximally there is less bone distributed further so the polar second moment of area is high

Question 8

Is cortical or cancellous bone weaker under axial loading?

Answer 8

cancellous

Question 9

Which parts of a long bone are made of cortical and which parts are made of cancellous bone?

Answer 9

mid-diaphysis = cortical 
metaphyses = cancellous

Question 10

Which fracture pattern is the result of pure bending?

Answer 10

transverse

Question 11

In a transverse fracture, which side is loaded in tension and which side in compression?

Answer 11

convex side in tension

concave side in compression

Question 12

In a transverse fracture, which side fails in

a) adults ?
b) children?

Answer 12

a) convex/tension side as it is weaker in tension than compression
b) concave/ compression

Question 13

Which fracture pattern is the result of pure compression?

Answer 13

oblique

Question 14

Which fracture pattern is the result of bending and compression?

Answer 14

butterfly segment

• bending causes transverse crack on tension side of bone
• compression causes an oblique fracture
• results in fragment on compression side of bone

Question 15

Which fracture pattern is the result of pure torsion?

Answer 15

spiral

Question 16

Why does a spiral fracture pattern form?

Answer 16

the fracture line at about 45° to the axis about which the torque is applied
failure of the bone in tension, perpendicular to the crack

Question 17

Which portion of the bone fractures under a compressive load?

Answer 17

close to or within the metaphyses

Question 18

How does rate of loading determine bone strength?

Answer 18

it is stronger at a higher loading rate than at a lower loading rate

Question 19

Describe the fracture process

Answer 19

1. energy to limb
2. energy soft tissues to bone
3. bone absorbs energy
4. bone fractures releasing energy into soft tissues
5. damaged bone and soft tissues bleed causing a haematoma
6. acute inflammatory response causes pain and healing

Question 20

How does the size of gap affect bone healing?

Answer 20

If the gap is small it heals but if large it does not

Question 21

What characterises fracture healing?

Answer 21

callus formation

Question 22

What is secondary bone healing?

Answer 22

callus developing, around the fracture site, from mesenchymal (primitive) tissue then chondroid (cartilage) and then osseous (bone) tissue. Later, remodelling takes place and the external callus gradually disappears as the bone regains its original strength, shape and internal architecture.

Question 23

How long does it take for most long bone fractures to heal?

Answer 23

6-12 weeks

Question 24

What happens to fracture if blood supply is not re-established?

Answer 24

bony union will not take place. This may be described as an “atrophic” or fibrous union

Question 25

What happens if there is excessive movement during fracture healing?

Answer 25

``` cartilage laid down instead of bone or pseudoarthrosis (false joint) may form ```

Question 26

What happens if there is no relative movement (or micromovement) taking place between fracture fragments during the healing process?

Answer 26

primary bone healing with no callus formation

Question 27

Is primary or secondary bone healing quicker?

Answer 27

primary gets its structure back quicker but not its strength

Question 28

What is the disadvantage of primary bone healing?

Answer 28

rigid fixation deprives bone of its natural loads causing stress shielding and weakness

Question 29

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

Answer 29

Wolff's law

Question 30

How does callus formation give structural support to a healing bone?

Answer 30

increases the second moment of area which compensates for the lower strength and rigidity of the material of the callus

Question 31

How does loading encourage bone union?

Answer 31

loading bone along long axis

Question 32

Name three possible factors which may explain why movement at the fracture site influences bone healing.

Answer 32

Electrical effects caused by moving crystals of hydroxyapatite, which are the basic mineral constituents of bone. Hydroxyapatite is known to be piezoelectric, that is it develops an electric charge when loaded. Hormonal factors (there is some evidence of a hormone “Substance P” being produced at fracture sites). Electro-magnetic effects produced through electron flow away from the fracture site.

Question 33

How much blood is lost from a) femoral fracture? b) pelvic fracture?

Answer 33

a) 1 litre | b) 3 litres

Question 34

What is the first step in fracture management?

Answer 34

reduction

Question 35

What is the second step in fracture management?

Answer 35

holding

Question 36

What are the two types of reduction?

Answer 36

open | closed

Question 37

What are the two types of holding?

Answer 37

internal and external fixation

Question 38

Give 3 methods of external fixation

Answer 38

plaster of paris traction external fixator

Question 39

What is the primary objective of all kind of fixation devices?

Answer 39

to minimise deformation (or movement) between the fracture fragments.

Question 40

How do splints work? when are they suitable?

Answer 40

stabilise soft tissues of a stable fracture to resist bending forces after reduction but are of little use in resisting torsional and compression forces

Question 41

What material is plaster of paris?

Answer 41

calcium sulphate

Question 42

What risk is there when using a plaster of paris cast?

Answer 42

produces heat when the crystal sets to a solid which may damage patient

Question 43

How is a plaster of paris cast made?

Answer 43

using cotton bandages, hard-coated with crystals of calcium sulphate hemihydrate getting wet and putting around splint

Question 44

In a plaster of paris cast what does a) the bandage provide? b) the starch provide?

Answer 44

a) vehicle | b) accelerates drying

Question 45

Give the two ways that plaster functions

Answer 45

1. hydraulic theory - rigid exoskeleton supports soft tissues which support the bone 2. periosteal hinge - three point bending fixates bone

Question 46

How do casts have to control the position of the bone?

Answer 46

1. length - prevent shortening 2. prevent A/P or medial/lateral tilt 3. rotation about long axis of bone

Question 47

In which way do externally applied splints struggle to control bone position? How is this controlled?

Answer 47

struggle with controlling rotation by applying to joint above and below

Question 48

Describe an advantage of a functional brace, compared to a full- leg cast.

Answer 48

dont immobilise the limb so muscles dont waste

Question 49

How is traction as a holding device difference to using traction to reduce a fracture?

Answer 49

traction reduces a fracture by controlled use of force on a relaxed limb in order to position bones Traction as a holding technique depends on altering muscle tone in order to maintain a position achieved at reduction.

Question 50

What role do the muscles play in holding a fracture, in traction?

Answer 50

The muscles increase in tone if subject to an increased load in traction, maintaining the position of the broken bone fragments.

Question 51

What is Static (fixed) traction?

Answer 51

load is applied to the limb and attached to a splint eg. Thomas' splint

Question 52

What is the disadvantage of using Static (fixed) traction?

Answer 52

immobilises the joint so there is no movement at fracture site + muscle weakness

Question 53

What is dynamic traction?

Answer 53

pulleys allow joint to move but with the net force along the axis of the bone

Question 54

Why is balanced traction used?

Answer 54

to offset the pressure effects caused by splints

Question 55

Give some general disadvantages of traction

Answer 55

prolonged hospitalisation + immobilisation Bed sores chest and urinary infections disuse atrophy of muscles and bone

Question 56

Name the factors taken into consideration when deciding on the method that will be used to hold a fracture.

Answer 56

the patient's age and functional requirements the method and character of injury: open/closed, high/low energy, soft tissue injuries available facilities skills of the operator