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BMSc Semester 2 > Lower Limb Biomechanics and Prosthetics > Flashcards

Lower Limb Biomechanics and Prosthetics Flashcards

1
Q

mean amputee age and main cause

A

69 years

80% PAD

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2
Q

what are the objectives of prothetic replacement

A

comfort
- socket fit, force transmission

function 
- stability, controlled movement

cosmesis

  • static (colour, shape, texture)
  • dynamic (gait pattern)
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3
Q

force transmission - what are the 3 types of force

A

support
- axial forces associated with BW bearing

stabilisation
- forces perpendicular to the axis of the limb and associated w/ moments acting around the joint

suspension

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4
Q

what are the components of the prosthetic that should be considered

A 
interface components
alignment components
functional components
cosmetic components 
structural components
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5
Q

what determines socket design

A

Level of the amputation

avoid loading pressure-sensitive areas

apply force to pressure-tolerant areas

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6
Q

what is Syme’s amputation

A

amputation through the ankle joint

disarticulation

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7
Q

what is transfemoral amputation also known as

A

above knee amputation

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8
Q

what are examples of suspension devices

A

cuffs and straps

  • pelvic belt (transfemoral)
  • supracondylar cuff (transtibial)

socket liners

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9
Q

what is the general functional requirements for prothesis

A

must be able to bear weight

and allow controlled movement

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10
Q

what are requirements for ankle-foot devices

A

absorb shock just after HS

allow smooth transition to foot-flat

resist dorsiflexion

provide push-off

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11
Q

what happens during HS in anatomical foot and what does the prosthetic ankle-foot need to replicate

A

first plantigrades then the ankle begins to plantarflex due to GRF acting behind ankle long axis

in normal gait, the pre-tibial muscles contract eccentrically to absorb energy

prosthetic must simulate this energy absorption

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12
Q

what happens during foot-flat in anatomical foot and what does the prosthetic ankle-foot need to replicate

A

ankle is around 10degrees plantarflexed - the plantarflexion moment reduces as the point of GRF moves anterior

Pretibial muscle activity falls

as GRF continues anterior of the ankle joint, the external moment becomes one of dorsiflexion

Prosthetic ankle-foot must allow a smooth, controlled transition to foot flat

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13
Q

what happens during mid stance in anatomical foot and what does the prosthetic ankle-foot need to replicate

A

ankle continues to dorsiflex-plantarflexors (soleus and gastrocnemius) control rate

prosthetic must simulate smooth, controlled, dorsiflexion

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14
Q

what happens during heel off in anatomical foot and what does the prosthetic ankle-foot need to replicate

A

ankle dorsiflexes to 15 degrees and calf muscles contract to counteract increasing dorsiflexion moment and provide active push-off

prosthetic allows controlled dorsiflexion to around 10 degrees. Some devices store energy which is then used to provide some active push off

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15
Q

what happens during toe off in anatomical foot and what does the prosthetic ankle-foot need to replicate

A

normal ankle has reached 20 degrees plantarflexion

prosthetic returns to the plantigrade position under the action of the energy-storing leaf-spring or compressed dorsiflexion “bumpers”

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16
Q

what happens during the swing phase in anatomical foot and what does the prosthetic ankle-foot need to replicate

A

normal ankle dorsiflexes slightly to improve toe-clearance at mid-swing

prosthetic remains plantigrade

17
Q

what are the 2 categories of ankle-foot devices

A

articulated

  • uniaxial
  • multiaxial

non-articulated

  • solid ankle
  • flexible ankle
18
Q

examples of the multi-axial prosthetic

A

Greissinger

Multiflex

19
Q

examples of the flexible ankle prosthetic

A

Flexfoot

20
Q

what is a SACH foot

A

non-articulated prosthetic

w/ solid ankle, cushion heel and stiff keel

21
Q

what are the principle requirements of the knee joints

A

stability in stance phase to support amputee’s weight

flexion in swing to allow clearance

22
Q

what provides stance stability in knee prosthesis

A

locks
- manual or semi-automatic

brakes

  • friction
  • hydraulic

polycentric knee
- 4-bar linkage

free knee
- stability achieved by combo of A-P knee axis position and residual muscle action

23
Q

how does friction work as a break

A

when weight is applied to the prosthesis, contact surfaces are pushed together and friction locks the knee

during swing phase, the springs keeps the surfaces apart, following flexion

24
Q

how does polycentric 4-bar linkage work

A

instantaneous centre of rotation of knee joint moves as angle of flexion changes

w/ knee straight the knee centre is high in the thigh and posterior to GRF, enhancing stability

25
Q

what is the requirements for swing phase control in knee prosthesis

A

allow knee to flex for toe clearance

control the heel rise immediately after toe-off

allow forward acceleration of the shank to ensure full knee extension at next heel-strike

control the knee extension so that terminal impact is minimised

26
Q

what are swing phase control types

A

friction control

hydraulic or pneumatic controls

27
Q

adv and disadv of friction as swing phase control

A

adv:
light in weight
reliable
can be adjusted by patient to suit walking speed

disadv:
cadence-specific (only works effectively at one walking speed)

28
Q

adv and disadv of hydraulic or pneumatic for swing phase control

A

Adv:
effective over range of cadences
can be controlled by microprocessor

Disadv:
heavy
requires more maintenance

29
Q

how do microprocessor controlled prothesis work

A

as patient walks faster, change in cadence is detected by electronics and motor closes value to stiffen the system

range of cadence over which the device is effective is increased

30
Q

what is the commonest alignment system used in knee prothesis

A

Pyramid system
- four adjustable grub-screws in an outer collar which bear on an inverted pyramid and allow angular adjustments of up to 15 degrees in any direction

31
Q

example of mis-alignment - prosthetic foot set too near the midline

A

causes the socket to try to rotate anticlockwise on residual limb, results in medial pressure proximally and lateral distally

remedy - shift foot laterally to bring line of action of GRF through mid-line of socket

32
Q

what is the outer covering of the prosthetic “skin” normally made from

A

fabric, PVC or silicone “skin”

BMSc Semester 2 (4 decks)

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