Implant technology Unit 6a

Question 1

Function of bones?

Answer 1

Support and protect internal organs, carry load and enable locomotion

Question 2

What 3 factors determines the location and mode of fracture?

Answer 2

The geometry and structure of the bone
The loading mode e.g. compression, bending, etc.
The loading rate

Question 3

Why do torsional fractures tend to occur at the distal tibia rather than proximal?

Answer 3

Because the polar moment of inertia is smaller distally compared to proximally

Question 4

What fracture type is seen after a pure bending force is applied?

Answer 4

Transverse fracture

Question 5

What fracture type is seen in pure compression?

Answer 5

Oblique fracture

Question 6

What fracture type is seen in combined compression and bending?

Answer 6

Butterfly type fracture

Question 7

What fracture type is seen in pure torsion?

Answer 7

Spiral fracture

Question 8

What fracture type is seen in high energy fractures?

Answer 8

Comminuted fracture

Question 9

Summarise the fracture process?

Answer 9

Energy is delivered to the limb
The energy is transferred via the soft tissue to the bone which absorbs the energy
The bone break and energy is released back to the soft tissue
The broken bone and damaged tissues bleed and cause a build up of blood around the damaged area. Such a blood collection is termed a haematoma
An acute inflammatory response occurs around the damaged area which causes pain to the victim and commences the processes which lead to healing

Question 10

What is the process of secondary (natural) bone healing?

Answer 10

Weeks 0-2: Haematoma is invaded by macrophages which clear up dead and damaged tissues and the haematoma

2-6: New capillaries grow into the fracture haematoma bringing with them cells of healing e.g. osteoblasts, fibroblasts, etc.

6-12: New bone tissue is laid down in the endosteal space from the residual living bone and eventually the two ends are reunited as a ball of provisional “callus”

Up to 12 months: Callus continues to form woven bone which gradually remodels to form a cortex

Up to 2 years: The callus matures so that the trabecular pattern is reformed and the bone is able to cope with stresses it encounters

Question 11

What is primary bone healing?

Answer 11

When there is no micromotion taking place, the fracture heals without external callus formation. New Haversian systems grow directly across the fracture gap. It is quicker than secondary bone healing but the bone isn’t initially as strong

Question 12

What is Wolff’s law?

Answer 12

Bone in a healthy person or animal will adapt to the loads under which it is placed

Question 13

Why is the rigidity of a recently fractured bone with a callus similar to the rigidity of the normal bone?

Answer 13

Although it’s Young’s modulus is reduced, the second moment of inertia is increased to compensate. As the callus hardens, the cross-sectional area decreases again

Question 14

Fracture management involves reduction followed by holding. How can a fracture be reduced?

Answer 14

Anaesthesia is often provided which relaxes the muscles which otherwise are in spasm and would make the process very difficult.
Closed reduction - manipulation of the fracture fragments
Open reduction - the fracture site is opened up surgically and fracture fragments are restored to alignment directly

Question 15

Give 3 examples each of internal and external fracture holding?

Answer 15

External:

• Plaster of Paris
• Traction
• External fixator

Internal:

• Plates and screws
• Compression screw
• Rods and nails

Question 16

What is plaster of Paris made of?

Answer 16

Calcium sulphate - it is extracted in crystal form and heated to remove the water and make calcium sulphate hemihydrate. When this compound is mixed with water, it forms crystals again and sets to a solid. It is an exothermic reaction and so care must be taken when applying to avoid damage to the patient’s skin

Question 17

What is a hard coated bandage?

Answer 17

Calcium sulphate hemihydrate is dissolved in ether which contain no water. Starch is added and the whole paste in coated on bandage. The wet bandage is then dried

Question 18

What effect does the starch have?

Answer 18

It doesn’t alter the strength of the cast, however it does speed up the setting process

Question 19

What other factors influence the speed at which the plaster of Paris sets?

Answer 19

The temperature of the water used

Retarders - slow the process e.g. alum and borax

Question 20

The plaster of Paris consists of two types of crystals. What effect does each have?

Answer 20

Some are long and sharp and others are shorter. The longer crystals occur naturally as alabaster (type of rock). They give the finished cast a hard quality. The smaller crystals give the cast a softer feel

Question 21

How does the plaster of Paris function? (2 ways)

Answer 21

By encasing the limb in a rigid exoskeleton it provides support to the soft tissues which in turn support the broken bone

By moulding the cast against the fracture it is possible to obtain a 3-point fixation system

Question 22

Disadvantages of a plaster of Paris?

Answer 22

If the casting is prolonged, the encased joints become stiff and muscles waste through disuse. This prolongs overall rehabilitation

Question 23

What is functional or cast bracing?

Answer 23

A combination of casting and hinges

Question 24

When are the braces suitable for application?

Answer 24

After 2-3 weeks when the soft tissue injury has settled and there isn’t swelling

Question 25

There are two new method of materials considered more adjustable than plaster of Paris. What are they?

Answer 25

Isoprene rubbers or polycaprolactone sheets

Glass fibre or artificial fibre and polyurethane composites

Question 26

How do polycaprolactone/isoprene sheets work?

Answer 26

They become ductile at fairly low temperatures allowing them to be moulded to the limb. At room temperature they become firm, but remain flexible enough to be gently adjustable, retaining a “memory” of their formed shape. It is however, an expensive option

Question 27

How do fibre/polyurethane composites work?

Answer 27

They consist of woven bandages of glass fibre or fabric which are impregnated with a urethane monomer and a catalyst. When exposed to warmth and moisture, this forms a true polyurethane/fibre composite which is very light and extremely strong, but still flexible

Question 28

Traction can be either skin traction or skeletal traction. What are the advantages and disadvantages of each?

Answer 28

Skin traction - the load is applied via a foam or sticky bandage applied to the skin. Although convenient, this method can only be used for loads up to 50N, above which would endanger the skin

Skeletal traction - load is applied via a pin inserted through the bone. Better for applying large loads and in dynamic loading. There is however, a risk of infection at the pin site

Question 29

What are the 3 types of traction?

Answer 29

Static (fixed) traction - load is applied to the limb and attached to a splint so that the splint itself provides the counter-force. E.g. Thomas’ splint

Dynamic traction - similar to static but a system of pulleys allows the limb to move more

Balanced traction - combination of both. Used principally to offset pressure effects caused by splints

Question 30

Disadvantages of static traction?

Answer 30

It is acceptable for a week or two but the immobility prevents joint movement, does not induce axial movement at the fracture site and leads to muscle disuse. It is mainly used to treat children’s fractures as they don’t cope well with complicated traction and their fractures heal quickly

Question 31

Complications of traction in general?

Answer 31

Associated with prolonged immobility - bed sores, chest and urinary infections, disuse atrophy of muscles and bones
Requires prolonged hospital stays - not practical for patient and expensive

HOWEVER, it is the safest form of treating fractures

Question 32

What factors are considered when deciding how to treat a fracture?

Answer 32

The patient
The injury type
The facilities available
The skills of the operator