Implant technology - unit 6A deck 2 Flashcards
What is the most common splitage material used ?
Plaster of Paris
How are commercial plaster of Paris bandages made and what is this type of bandage knwon as ?
- They are made by dissolving calcium sulphate hemihydrate in an organic solvent, such as ether, which contains no water.
- Starch is then added to this mixture and the whole paste is spread on a cotton bandage.
- This wet bandage is then dried. The bandage is therefore coated with calcium sulphate ‘held on’ by starch
This is known as a hard coated bandage.
What is a plaster of Paris cast made using
- Hard coated bandages are used (cotton bandages, hard-coated with crystals of calcium sulphate hemihydrate)
- Water is used to wet the bandages
- The bandage adds little to the strength but provides a vehicle for getting the wet plaster on to the part to be splinted
- The bandage consists of cotton thread which may be double woven to prevent it fraying (known as leno cloth).
what influences the speed of setting of a plaster of paris cast
- the starch known as an accelerator, it speeds up the chemical reaction
- also the temp of the water
What materials can be added to a plaster of Paris cast to slow down the setting process?
Retarders e.g. alum and borax
When applying a plaster of Paris cast why is there a risk of causing damage to the patient ?
considerable heat production when calcium sulphate hemihydrate mixed with water, if care isn’t taken could result in damaging the patient
what are the two types of crystals that make up the POP cast and what properties do they confer to the cast?
2 types:
- Long and sharp - known as alabaster, they give the cast hard quality
- Smaller - they give the cast a softer feel
properties of the material of the final splint are largely dependent on the physical interlocking of the 2 types of crystals
The interlocking between the 2 crystal types is influenced by what ? and how does this affect the setting of POP casts?
Influenced by how wet the plaster material is at the time of application.
- Excess water is required to make a plaster bandage workable, this means that the excess water must evaporate before the cast is strong enough to bear weight.
- This may take up to two days in a typical cast. This inevitable weakening of a plaster cast is unfortunately necessary to give plaster that versatility of application which makes it such a useful material.
What are the 2 ways in which a POP cast functions and what is the main function
- Encases the limb in a rigid exoskeleton it provides support to the soft tissues which in turn support the broken bone. This so called hydraulic theory has been well proven.
- By moulding the cast against the fracture it is possible to obtain a gentle three point fixation system, giving a so-called periosteal hinge.
- [Most casts work by a combination of both methods, the 1st predominates in most situations except in childhood when the tough periosteum provides a gentle hinge about which fulcrum a three point mould can be achieved (can see this in the pic)]
most cast have to control the position of a broken bone in three dimensions - these dimensions are
- Length i.e. prevent shortening
- Position i.e. prevent tilt and shift in anterior/posterior and medio/lateral planes
- Rotation i.e. about the long axis of the bone
In externally applied splits (casts) which of the 3 dimensions it controls is the most difficult to control?
Rotation
How do casts control rotation ?
by incorporating the whole of the broken bone and limb segment in the cast including the joint
What is the disadvatange of casting technique which incorporate the joint into the cast?
- If casting is prolonged the encased joints become stiff and their muscles waste through disuse. This prolongs overall rehabilitation.
- Also during casting, the impairment caused by immobilisation of joints may lead to disability sufficient to induce dependency and prolong the stay in hospital - especially for elderly patients.
how can the problems that come from immobilisation with a cast be overcome
- Careful moulding and the application of hinges incorporated into the cast.
- This technique, known as functional or cast bracing
how does a functional cast work in a femoral brace
the upper third of the femoral component is gently squared off so that the soft tissues are slightly distorted but not sufficiently to raise high points of pressure
knee is freed by the use of hinges which permit the knee to move normally
the position of the broken fragments are held reduced whilst the joints move normally and the muscles can rehabilitate early.
how does Sarmiento’s classic brace for tibia fractures work
achieves rotatory control through moulding around the upper third of the tibia and by extensions to the cast which encaptures the femoral condyles in knee flexion.
why do braces only applied after the first two/three weeks after fracture
so the soft tissue injuries have settled down and there is no swelling
Why should braces be ideally adjustable?
Because they always need to be in contact with the skin
what are the classes of new materials of adjustable braces
- isoprene rubbers (or polycarprolactone sheets) and glass fibre
- artificial fibre and polyurethane composites
what are the properties of Polycaprolactone/isoprene sheets
They become ductile at fairly low temperatures, so that whilst warm they can be moulded directly onto the skin achieving a reciprocal shape to the limb
When at room temperature they become firm, but remain flexible enough to be gently adjustable, retaining a “memory” of their formed shape.
what is disadv of Polycaprolactone/isoprene sheets
- expensive - require purchase of an oven
- require a lot of skill
what do Fibre/polyurethane composites consist of
woven bandages made of glass fibre or fabric which is impregnated with a urethane monomer and a catalyst
why are Fibre/polyurethane composites useful
When exposed to warmth and moisture, forms a true fibre/polyurethane composite which is very light and extremely strong, yet flexible
when are Fibre/polyurethane composites useful and when are they not
- Forming braces when they are applied to a reasonably stable, healing fracture as they can form very sophisticated shapes and interface well with hinge materials, ensuring a firm anchorage.
- Make excellent secondary casts once swelling has settled and the soft tissues confer a degree of stability to a fractured limb.
[They are not very useful as a primary splintage material as they are conforming rather than being very mouldable and are difficult to use on unstable and swollen limbs.]
why does POP remain the mainstay of treatment for low velocity fractures
- cheap
- easy to obtain
- easy to apply
- very versatile
It is messy, and a little brittle but in general its advantages outweigh its disadvantages.
Describe an advantage of a functional brace, compared to a full- leg cast.
Allows movement at the joints and helps to reduce muscle wasting due to immobility
Appreciate this:
It is important to emphasise that traction, which literally means pulling, is a method of holding fractures and is quite separate to the sorts of pulling that might be required to reduce a fracture.
How does traction as a holding technique work?
it works by using a controlled force which alters (increases) muscle tone in order to maintain a position achieved at reduction.
What do all muscles resist ?
Stretching and if muscles are subject to a slight increase in load of say 70 or 80 N then the result will be a small but marked increase in muscle tone.
what load is needed for traction in the lower limb and why is a counter force needed?
- 10N per 100N of BW
- This must be countered by an equal force achieved by tilting the bed backwards otherwise patient would be pulled out of the bed ==> using body weight and the frictional resistance between the patient and the bed
what are the two ways load may be applied to the limb in traction
- skin traction
- skeletal traction
how does skin traction work
- load is applied via a foam or sticky bandage applied to the skin.
- The attachment to the limb is dependent on the adhesiveness of the bandage or the frictional resistance of the foam.
- This method, although convenient, can only be used for loads up to 50 N as otherwise there is a very real danger of injuring the skin.
how does skeletal traction work
- load is applied via a pin inserted through the bone.
- can be used to apply large loads and has advantage that the load can be precisely relative to the long axis of the bone - this is important when traction is being used in dynamic situations.
What is the disadvantage of skeletal traction ?
Risk of bone infection at the pin bone interface
[can be countered by careful pin insertion and good pin site care by nursing staff]
what are the 3 methods of traction
- static (fixed) traction
- dynamic traction
- balanced traction
Describe static (fixed) traction and an example of it
Load is applied to the limb and attached to a splint so that the splint itself provides the counter force e.g. Thomas splint
pic shows winders producing the force and the counter force produced by the outer shell of the splint
What are the disadvtanges of static traction
Only acceptable for a week or two as it causes immobility which prevents joint movement, does not induce axial movement at the fracture site and leads to muscle disuse.
when is static traction used
mainly used for treating children’s fractures because they do not cope well with complicated traction and their fractures heal quickly.
how does dynamic traction work
- The joints are permitted to move and the load is arranged so that, irrespective of limb position, the net pull is maintained along the axis of the bone.
- This is achieved by using pulleys
what are the functions of the pulleys in dynamic traction
- They alter the direction of the force by being statically mounted on a surrounding bed frame
- They may alter the magnitude of the traction force by being mounted on the limb or “free floating” within the traction cord system.
when are free floating pulley systems useful in dynamic traction
Useful when the physiotherapist wants to counter the weight of a limb segment so that very weak muscles can be exercised without the full weight of the limb early in treatment.
when and why is balanced traction used
used as a supplement to either static or dynamic traction
used to offset pressure effects caused by splints
i.e. used for Thomas splints where a counter force is applied to the groin
how can pressure effects be offset in the Thomas splint
by applying a small load to the splint as a whole which tends to draw the pressure off the groin area
What are the general complications of traction
Due to prologned periods in bed:
- bed sores
- chest infection
- UTI
atrophy of muscles and bones
[need active physio program]
What is the safest method of treating fractures and why
Traction - because there is easy access to the fracture and difficulties with alignment can be easily observed and corrected
why is traction not used very often
requires long period of hospitalisation (upto 3 months)
what makes fractures heal faster
- When the bones are in reasonable apposition
- Subjected to axially orientated [not shearing] loads
- little bit of movement
When does plaster cast fracture fixation work well?
In low energy fracture situations, where soft-tissue damage is minimal
what factors need to be considered when deciding on Tx of a fracture
the patient
the injury
the facilities available
the skill of the operator
what needs to be considered about the patient
Fracture fixation technique to individual patients will take into account the functional requirements of an individual depending on their age and health.
age
- elderly have more co-morbities
- children, bones heal more rapidly and have more capacity to naturally remodel their shape after fracture
health
- co-morbidites
- functional requirements
What needs to be considered about the injury in deciding the method of treatment
- Although X-rays of injuries may look like each other, the causative force may be quite different.
- The fracture may be open and contaminated, or closed.
- The risk of infection will affect the method of holding. Associated injuries to ligaments, blood vessels or nerves may make the surgeon more likely to operate than to treat non- surgically.
What role do the muscles play in holding a fracture, in traction?
The muscles increase in toneif subject to an increased load in traction, maintaining the position of the broken bone fragments
