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Lower Limb Biomechanics and prosthetics > Ken Mac Lecture > Flashcards

Ken Mac Lecture Flashcards

1
Q

What is an external limb prosthesis

A

An externally applied device used to replace, wholly or in part an absent or deformed limb segment

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2
Q

Stats on NHS Tayside Prosthetics Service

A
  • covers 750k population
  • 100 amputations per year of which 60% are fitted with a prosthetic
  • mean age 69 years
  • 80% peripheral arterial disease
  • 95% lower limb
  • case load ~ 750 prosthesis users
  • trans tibial 55%, trans fermoral 37% 8% other
  • Multidisciplinary team approach
  • majority LL
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3
Q

Objectives of prosthetic replacement

A

comfort

- socket fit, force transmissin
function
  • stability, CONTROLLED movement

cosmesis

  • static (colour, shape, texture)
  • dynamic (gait pattern)
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4
Q

list the 5 prosthetic components

A 
interface 
alignment 
functional  
cosmetic 
structural
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5
Q

Describe the interface component

A

support force
- axial and proximal direct forces associated with the bearing of body weight
stabilisation forces
- act perpendicular to the longitudinal axis of the lim and are associated with the resistance to moments acting around the joint
suspension Forces
- anatomical
- pressure differential (suction)

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6
Q

Alignment component

A

allow the relative positions and angles of components to be changed so that the magnitude and lines of action of forces can be altered and the moments acting round joints to be changed to ensure an efficient, comfortable and cosmetic gait patten

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7
Q

Magnitude and distribution of forces at the residual limb/socket interface can also be influenced by …..

A

alignment changes

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8
Q

what is the commonest alignment system

A

pyramid system
- uses 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

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9
Q

What is the remedy for a prosthetic foot set too near to the mid-line of the body?

A

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

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10
Q

What is the remedy for a knee forced into hyperextension?

A

A) if the p. is able to bear weigh equally between heel and forefoot = dorsiflex foot to allow knee to adopt a more normal posture
B0 is the p. is bearing weight excessively on the heel = shift foot posteriorly to move GFR closer to knee and reduce hyper-flexion MOMENT

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11
Q

Structural component

A

need to be able to withstand the force and moments to which they are subjected to.
e.g. shin tube, connects the knee joint to the angle-foot device, may have an integral alignment unit built into it

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12
Q

cosmetic component

A

usually consist of a foam “tube” shaped internally to fit the component and externally to match the limb

surface treatment of the foam cover can vary depending upon the patients requirement sand the cost but usually consists of a fabric, PVC or silicone “skin” which is applied over the foam
Wood and medal surface can be treated in the same way

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13
Q

Ankle-foot device requirements

A
  • absorb shock just after heel strike
  • allow a smooth transition to foot-flat and through mid-stance
  • resist dorsiflexion and, if possible, store energy from mid-stance to heel-off
  • provide push off- through energy return during late stance
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14
Q

Normal heel strike

A

foot is plantigrade –> ankle begins to plantar flex due to the GRF being behind the ankle joint

pretibial muscles contract to eccentrically absorbing energy

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15
Q

Normal foot flat

A

ankle is in ~10 degrees plantar flexion

  • plantar flexion moment reduces as the point of application of the GRF moves anteriorly
  • pretibial muscle activity falls off
  • as the GRF starts to pass anterior to the ankle joint, the external moment becomes one of dorsiflexion
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16
Q

Normal mid-stance

A

ankle continues to dorsiflex

- plantar flexors (soles & gastrocnemius) control rate by contracting eccentrically

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17
Q

Normal heel off

A

ankle dorsiflexes to ~15 degrees and calf muscles contract strongly to counteract the increasing dorsiflexion moment and provide active push-off to propel the subject forward

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18
Q

Prosthetic Ankle-foot device

Heel off

A

allows controlled dorsiflexion to ~10 degrees during which time some devices store energy which is then returned to provide some active push-off

19
Q

Prosthetic Ankle-foot device

Toe off

A

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

20
Q

Prosthetic Ankle-foot device

Swing phase

A

device remains plantigrade

21
Q

During normal toe off what angle has the ankle acheived?

A

~20 degrees plantar flexion

22
Q

Swing phase

- what does the ankle do and why?

A

flexes slightly to improve toe-clearance at mid-swing

23
Q

Prosthetic Ankle-foot device

Heel Strike

A

ankle device must stimulate the energy absorption of the GRF

24
Q

Prosthetic Ankle-foot device

Foot Flat

A

device must allow a smooth controlled transition

25
Q

Prosthetic Ankle-foot device

Mid-stance

A

device must stimulate smooth, controlled dorsiflexion

26
Q

Prosthetic Ankle-foot device

Mid-stance

A

device must stimulate smooth, controlled dorsiflexion

27
Q

Name two examples of a articulated multaxial ankle-foot device

A

Greissinger

Multiflex (15 degree P/ 10 degrees D)

28
Q

Name an example of a non-articulated flexible ankle-foot device

A

flexfoot

29
Q

Name an example of a non-articulated heel spring and flexible keel ankle-foot device

A

quantum foot

30
Q

Name an example of a non-articulated stiff keel ankle-foot device

A

SACH

31
Q

Name an example of a non-articulated flexible keel ankle-foot device

A

seattle

32
Q

Costsof ankle-foot devices

A

SACH 60
Pathfinder 1,800
Flexfoot 800 to 3k

33
Q

Principle requirements of a prosthetic knee

A

Stability (instance phase to support the amputee’s weight)

Flexion (in swing to allow clearance)

34
Q

Stance Stability of the knee

  • what types of locks can be used?
  • if the free knee method is employed how is it achieved?
A

Free knee- stability is achieved by a combination of A/P knee axis and residual muscle action (alignment stabilty)
locks- manual or semi-automatic
brakes- friction or hydraulic
polycentric

35
Q

Knee locks

  • Manual
  • Semi-automatic
A

Manual
- can engage for stability over rough ground or can walk with the knee unlocked (stability is achieved by residual muscles)
Semi-automatic
- locks automatically lock on extension but can unlock manually for sitting down

36
Q

Brakes- friction

A

weight is applied to the prosthesis, the contact surfaces are push together and friction locks the knee
during swing phase, the spring keeps the surfaces together

37
Q

Brakes- hydraulic

A

weight activated
a mechanical linkage closes a valve in hydraulic cylinder circuit, stopping the flow of fluid and effectively locking the piston

38
Q

polycentric knee mechanism

A

instantaneous centre of rotation (changes as the knee flexes)
with the knee straight the knee centre is high in the thigh, and posterior to the GRF, enhancing stability

39
Q

Swing phase control requirements of the knee

A
  • allow the knee to flex for toe clearance
  • control the heel rise immediately after toe-ff
  • allow forward acceleration of the shank to ensure full knee extension (and stability) at next heel-strike
  • control the knee extension so that terminal impact is minimised
40
Q

Knee swing phase control friction brakes

- pros and cons

A 
pros
- relatively light in weight 
reliable 
can be adjusted by patient to suit individual walking speed
- cost (300)  
cons 
- cadence-specific
41
Q

Knee swing phase control hydraulic and pneumatic

- pros and cons

A 
pros
-effective over a range of cadences 
- can be controlled by microprocessor 
cons
- heavy 
-requires more maintenance 
- jolly expensive (~ 12k)
42
Q

What is great about the Otto Bock C-leg?

A

automatic control of the valve “leak rate”, the amputee is able to walk down stairs and slopes “foot-over-foot”

43
Q

Combined stance and Swing control

A

combine it in one hydraulic unit and can be configured to allow “yielding” knee flexion in stance-phase which enables the patient to walk foot over foot down stairs and slopes
can also incorporate a manual lock

44
Q

Ossur power knee

A

microprocessor controlled and motorised active knee extensions ( costs 75k)

Lower Limb Biomechanics and prosthetics (4 decks)

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