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bmsc prosthetics > Unit 3: Lower Limb Prosthetics > Flashcards

Unit 3: Lower Limb Prosthetics Flashcards

1
Q

What are the 3 specific goals of prosthetic treatment

A

Comfort
Function
Cosmesis

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2
Q

How are prosthetic joints controlled

A

Remaining musculature

Control mechanisms

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3
Q

What are the 2 main elements of cosmesis

A

Static cosmesis and dynamic cosmesis

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4
Q

Name the 5 main components of a prosthesis

A 
Interface 
Structural
Functional
Alignment
Cosmetic
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5
Q

Interface components are exposed to support, stabilisation and suspension forces. What are the differences between these

A

Support: longitudinal forces that are proximally directed
Stabilisation: transversely directed component of the GRF
Suspension forces: longitudinal distally directed forces

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6
Q

In disarticulations, which region of the socket is shaped to provide the principal support forces

A

The distal region: large surface area, pressure tolerant tissue

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7
Q

In transection amputations, which region of the socket is shaped to provide the principal support forces

A

The proximal regions: because the cut ends of long bones have pressure sensitive tissue

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8
Q

What are the 2 methods of socket suspension

A

Anatomical: anchoring to the underlying anatomy

Pressure differential/suction

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9
Q

What kind of prosthesis applies the ‘socket philosophy’

A

The patella tendon bearing

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10
Q

What would be the effect of moving the foot of a trans-tibial prosthesis laterally upon a) the magnitude of the stabilising forces in the coronal plane b) the appearance of the patient’s gait

A

a) reduced magnitude of forces

b) wide based gait

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11
Q

Identify examples of functional components of lower limb devices

A

Ankle-foot devices
Knee units
Hip units

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12
Q

What are the 2 requirements of a functional component

A

Bear the weight of the amputee

Allow for controlled movement

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13
Q

What are the 2 main categories of ankle-foot devices

A

Articulated and non-articulated

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14
Q

What are the divisions of an articulated ankle-foot device

A

Uniaxial and multiaxial

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15
Q

What are the divisions of a non-articulated ankle-foot device

A

Solid ankle and flexible ankle

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16
Q

What 2 heel types can a solid non-articulated ankle foot device have

A

Cushioned heel and spring heel

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17
Q

What are the 2 types of cushioned heel

A

Stiff keel and flexible keel

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18
Q

What is the difference in how movement is achieved between articulated and non-articulated devices

A

Articulated: movement of adjacent parts of the device

Non-articulated: deformation of parts of the device

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19
Q

What is a disadvantage of the uniaxial articulated ankle foot design

A

The dorsiflexion bumper is unable to reproduce the action of the plantarflexor muscles from heel rise to toe off

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20
Q

How does the uniaxial ankle foot design differ from the multiaxial design

A

The multiaxial design allows for dorsi/plantar flexion as well as inversion/eversion

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21
Q

Which ankle foot device uses a rubber ball design to allow dorsi/plantarflexion, inversion/eversion and some internal/external rotation

A

The Multiflex ankle-foot device

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22
Q

Name an example of a non-articulated rigid ankle design

A

The SACH foot (the solid ankle cushion heel)

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23
Q

What flexible ankle design has been particularly useful for track athletes

A

Carbon fibre leaf springs (able to return some energy stored during roll over to the foot during push off)

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24
Q

What are the requirements of a prosthetic knee unit during a) stance phase and b) swing phase

A

a) remain stable to support body weight
b) allow for controlled flexion = allows leg to swing through without contacting the ground. Also allow for full extension = allows amputee to place weight upon it on heel strike

25
Q

What is the difference between a manual and a semi-automatic knee lock

A

Manual: amputee controls when the leg is locked/unlocked

Semi-automatic: leg locks when it goes into full extension

26
Q

How can an amputee ensure a locked extended knee makes proper contact with the ground

A

Vaulting (rising up abnormally high on the opposite leg)

Circumducting the hip

27
Q

What happens to knee stability as the knee unit axis becomes more posterior

A

The knee becomes more stable

28
Q

What is the zone of voluntary stability

A

The region between the line of action created by hip extensor muscle action that achieves knee stability at heel contact, and the hip flexor muscle action that initiates flexion at toe off

29
Q

What is the relevance of the zone of voluntary stability

A

If the axis of rotation of the knee unit is located in this zone, then the leg will be stable at heel stroke and early stance, but in late stance, knee flexion will be initiated

30
Q

What is a method used to overcome a smaller zone of voluntary stability at the knee in an elderly patient

A

Use of a polycentric knee unit: allows knee unit movement to occur at an axis higher in the thigh within their zone of voluntary stability

31
Q

What feature of a polycentric knee unit allows it to do so

A

It creates a polycentric axis of rotation

32
Q

How does a knee brake function

A

Allows the knee to swing freely, but locks when weight is placed on it due to contact between the surfaces

33
Q

List the 3 types of knee unit swing phase control mechanisms

A

Constant friction
Extension assist
Hydraulic or pneumatic systems

34
Q

What is one problem with extension assist mechanisms

A

They don’t adapt to changes in walking speed

35
Q

What are the main elements of a Canadian hip prosthetic unit

A

Free hinge hip unit placed anteriorly on the socket
Rubber bumper placed posteriorly to resist hyperextension
Knee unit placed posteriorly to the line between hip unit axis of rotation and point of heel contact
An elastic strap to assist knee extension during swing

36
Q

What allows the knee unit to flex in a Canadian hip prosthetic unit

A

Keeping the pelvis in an upright alignment: GRF passes behind the knee unit centre of rotation

37
Q

What changes can alignment components permit

A

Change in joint range of motion
Change in timing of different phases of gait cycle
Change in magnitude and distribution of the stump/socket interface forces and stabilising forces
Change in the external moments about joints causing a change in muscular activity

38
Q

What is the difference between integrated and transferred alignment units

A

Integrated: remain in the prosthetic unit as part of its structure
Transferred: removed from the prosthesis when it is being finished, replaced by a structural component

39
Q

What are the 2 mechanisms of integrated alignment unit

A

Sliding mechanisms and pyramid mechanisms

40
Q

What are the possible adjustments that an alignment component can allow for

A 
Lengthening/shortening
ML shift
ML tilt
AP shift
AP tilt
Internal/external rotation
41
Q

What are the 3 stages of an alignment process

A

Bench alignment: performed by a technician assembling the prosthesis
Static alignment: amputee wearing the prosthesis
Dynamic alignment: amputee walking wearing the prosthesis

42
Q

How can excessive proximal medial stump pressure in a PTB be adjusted

A

Tilt foot laterally (if foot is not flat on the ground)

Shift foot laterally

43
Q

How can the problem of the knee being forced rearwards in the PTB be adjusted

A

Dorsiflex the foot

Shift foot posteriorly (if patient bearing excessive weight on the heel)

44
Q

How can the problem of excessive knee flexion in the PTB be adjusted

A

Plantarflex the foot

45
Q

What are the 3 main types of body image

A

‘On face’ = mirror image
How other people see them
Someone’s inner image of themselves

46
Q

What is the difference between endoskeletal and exoskeletal components

A

Endoskeletal: structural components that are covered by cosmetic components
Exoskeletal components: structural components which also provide the external surface of the cosmesis, therefore must also function as cosmetic components

47
Q

Why are Syme’s or knee disarticulations not as cosmetic as others

A

Bulkier because must enclose the distal condyles

48
Q

What is the first stage of producing a socket

A

Take a negative cast of the stump using plaster impregnated bandages

49
Q

In what areas are plaster a) added to the cast or b) removed from the cast

A

a) where pressure relief is needed

b) where load bearing is to be encouraged

50
Q

What is the principle of a CAD/CAM system

A

A shape sensing system used to capture the shape of the stump using a computer. Aims to replace the manual casting and rectification process

51
Q

What are the 2 methods of CAD/CAM used

A
  1. Beam of laser light projected onto the stump, cameras capture the appearance of the line from different angles to reconstruct a profile of the stump
  2. Negative cast of the stump is taken then placed on rotatory a table. Mechanical arm within the cast rotates and moves up and down to reconstruct the stumps profile
52
Q

Advantages of CAD/CAM

A

Cleaner and quicker than manual socket fabrication
Can store shape info on a computer to allow for easy future modification if required
Can perform accurate research into the improvements to socket fit achieved by precise modifications in socket shape

53
Q

Disadvantages of CAD/CAM

A

Takes out the ability to actively mould the cast
May be difficult to interpret modifications from a computer screen
Requires new learning

54
Q

What are the 2 groups of testing that a prosthetic must undergo

A

Principle testing

Supplementary testing

55
Q

Give examples of principal tests that are performed

A

Static tests

Cyclic tests

56
Q

Describe a static test

A 
2 components (proof and failure test)
Proof test = single application (for 30 secs) of a specified load that corresponds to the worst load generated during an anticipated activity
Failure test = if sample withstands proof test, then load until it either breaks or fails
57
Q

Describe a cyclic test

A

Testing the fatigue properties of the prosthesis by applying a pulsating test force that oscillates sinusoidally between min and max force for the test

58
Q

Give examples of supplementary tests

A

A torsional test
An ankle foot device test (load the forefoot and ankle alternatively)
Knee flexion stop test (tests function during kneeling/squatting)
Knee lock mechanism

bmsc prosthetics (4 decks)

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