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735: Orthotics and Prosthetics > Lever Arms, Rockers, and GRF's > Flashcards

Lever Arms, Rockers, and GRF's Flashcards

1
Q

What are lever arms?

A

rigid structures through which a force can be applied to produce rotational motion about a fixed radius

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2
Q

How are lever arms determined?

A

By the perpendicular distance between the action of the vector (GRF) and the center of joint rotation

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3
Q

Define ground reaction force (GRF)

A

the force exerted by the ground on a body in contact with it

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4
Q

The rotational potential of the forces that act on a joint is called _____.

A

torque

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5
Q

Torque (M) = ______ x ______

A

amount of force (F) x lever arm (L)

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6
Q

The ground reaction force vector is the _____ load-bearing line, which takes into account the forces acting in all 3 planes.

A

mean

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7
Q

From initial contact through loading response there is a ____flexion moment. Explain why…

A

plantar

Because the force vector is behind the ankle

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8
Q

From midstance through toe-off there is a ____flexion moment. Explain why…

A

dorsiflexion

Because the GRF vector moves from behind the hell towards the forefoot

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9
Q

Orthotists describe _____ transitional periods, or rockers, during stance phase of walking as the body progresses forward over the foot.

A

three

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10
Q

Describe what happens during the first rocker

A

There is controlled lowering of the foot from neutral ankle position at initial contact to a plantarflexed foot flat, as well as acceptance of body weight on the limb during loading response

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11
Q

Where is the fulcrum at during the first rocker?

A

the heel

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12
Q

What muscles are active during the first rocker?

A

eccentric contraction of the quadriceps and anterior tibialis prevents “foot slap” and protects the knee as GFR is translated upward toward the knee

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13
Q

During the first rocker the foot ____ with flattening of medial arch, and thehind foot is positioned in ____ to allow absorption

A

pronates

valgus

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14
Q

What are 3 situations in which the first rocker is lost?

A
  • heel pain (plantar fasciitis, bone spur, etc.)
  • fixed equinus (foot lacks dorsiflexion, toe walkers)
  • true or apparent Lower Limb Deficiency
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15
Q

Describe what happens during the second rocker

A

The tibia begins to rotate over the weight-bearing foot, from its initial 10 degrees of plantarflexion at the end of loading response, then through vertical into dorsiflexion as midstance is complete

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16
Q

What muscles are active during the second rocker?

A

Eccentric contraction of the gastroc and soleus muscles puts on the brakes to control the speed of the forward progression of the tibia over the fixed foot throughout midstance

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17
Q

During the second rocker there is maximal _____ of the foot

A

pronation

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18
Q

Describe what happens during the third rocker

A

The forefoot is converted from its mobile adaptor function of early stance to a rigid lever for an effective late stance, and the heel rises off the ground so that the body weight has to roll over the first metatarsophalangeal joint through push-off in terminal stance

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19
Q

During the third rocker the foot moves into _____ and the heel is positioned in _____.

A

supination

varus

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20
Q

What muscle locks the midfoot during the third rocker so that the foot can act as a rigid lever?

A

tibialis posterior

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21
Q

What are 3 situations in which the third rocker is lost?

A
  • painful forefoot (Hallux valgus/hallux rigidus)
  • excessively stiff toe of prosthesis
  • loss of PF (neuromuscular, stiff hindfoot, ruptured Transverse Arch)
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22
Q

In summary:

1st Rocker Phase occurs during _______
2nd Rocker Phase occurs during _______
3rd Rocker Phase occurs during _______

A

Heel Strike

Stance Phase

Toe Off

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23
Q

What are 4 functions of prosthetic feet?

A
  • provide controlled plantarflexion at loading response
  • provide easy movement from hindfoot to forefoot
  • control large dorsiflexion moment at terminal stance to prevent collapse over the ankle
  • may try to give some motion at the MP joint (in some prosthetic feet)
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24
Q

What are 2 things prosthetic feet may not be able to eliminate?

A
  • a loss of plantar flexion during pre-swing

- a loss of dorsiflexion during swing phase

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25
Q

A soft heel = _____ heel lever which tends to increased stability at the knee

A

shorter

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26
Q

A soft heel allows for _____ foot flat

A

quick

easy PF movement

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27
Q

A firm heel = _____ heel lever which tends to decreased stability at the knee

A

longer

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28
Q

Although a longer heel lever leads to instability at the knee during the loading response it also has benefits, what are they?

A

It preserves more momentum and creates a better first rocker (the heel “rocker”)

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29
Q

A firm heel allows for _____ foot flat

A

slow

slower PF movement

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30
Q

Because soft heels have quick shortening of the heel lever there is a _____ PF moment whereas firm heels have a slow shorthening of the heel lever and a ______ PF moment

A

low

larger

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31
Q

In regards to toes, a rigid toe allows for easier _____, whereas a softer toe allows for easier ______.

A

push off

roll over

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32
Q

Where will the COP be in rigid toes?

A

at the end of the foot

33
Q

Where will the COP be in soft toes?

A

near the MP joint

34
Q

Rigid toes have a ____ toe lever

Soft toes have a ____ toe lever

A

long

short

35
Q

Rigid toes have a ____ dorsiflexion moment

Soft toes have a ____ dorsiflexion moment

A

high

smaller

36
Q

Rigid toes have a ____ knee extension moment

Soft toes have a ____ knee extension moment

A

high

lower

37
Q

What are the 3 advantages of having a stiffer ankle?

A
  • easier to stand without effort
  • increases control
  • more energy can be stored
38
Q

Typically K1 level patients use a _____ ankle foot

A

solid

39
Q

K2-K4 patients use a _____ or _____ ankle foot

A

single or multi-axial rollover

40
Q

What are the 6 functions of prosthetic knees?

A
  • provide stance stability early in stance phase
  • control heel rise during initial swing
  • control extension during terminal swing to prevent terminal impact
  • provide shock absorption at loading response
  • provide easy initiation of knee flexion at terminal stance
  • provide easy flexion during preswing
41
Q

What is a good starting point in regards to knee types for a patient who can vary their cadence?

A

a fluid control knee

42
Q

The _____ the heel lever of the prosthetic foot, the more it is encouraging knee flexion at loading response which requires increased quad control

A

longer

43
Q

A foot that is too stiff can cause excessive knee ______.

A

hyperextension

44
Q

Excessive plantar flexion can correlate with knee ______.

Excessive dorsiflexion can correlate with increased knee _____.

A

hyperextension

flexion

45
Q

Stride length should be equal bilaterally and is usually __ cm in males and __ cm in females.

A

80

65

46
Q

What are a few examples of pre-gait training drills?

A
  • standing the parallel bars
  • weight shifting
  • SLS
47
Q

What are 3 gait deviations observed without adequate single limb WB?

A
  • Decrease stance time on prosthetic limb
  • Decreased stride length on sound side
  • Lateral trunk bending over prosthetic limb
48
Q

Describe the protocol for prosthetic gait training (5 steps)

A

1) Prosthetic Limb Stepping (FWB)
2) Sound Limb Stepping (FWB)
3) Stride Length & Prosthetic Control
4) Ambulating with prosthesis in parallel bars
5) Ambulating with prosthesis using AD

49
Q

Amputees typically have ____ arm swing on prosthetic side

A

decreased

50
Q

When initiating sidestepping, should you step to the sound or prosthetic side first?

A

sound side

51
Q

What is normal cadence?

A

2.5 mph

52
Q

Most amputees use the step-to technique when ascending/descending stairs, however what amputee types may be able to do them reciprocally?

A

BKs and some AKs

53
Q

Why do ramps and hills tend to be difficult for amputees?

A

Due to a lack of adequate PF and DF

54
Q

What can be defined as the tendency for a movement?

A

Moment

55
Q

In order for there to be a flexion moment the GRF must be ______ to the knee

A

posterior (behind)

56
Q

How is a flexion moment produced in regards to foot positioning?

A

by moving the foot behind the knee

57
Q

In order for there to be a extension moment the GRF must be ______ to the knee

A

anterior (in front)

58
Q

How is an extension moment produced in regards to foot positioning?

A

by moving the foot forward under the knee

59
Q

Where should we place the foot in a BK amputee and why?

A

Behind the knee to promote knee flexion so they don’t hyperextend their knee and wreck their own knee ligaments/capsule

60
Q

Where should we place the foot in a AK amputee and why?

A

Under the knee or slightly in front to promote knee extension to increase knee stability

61
Q

What is the purpose of dorsiflexing the foot?

A

in promotes knee flexion which stops the knee from hyperextending

62
Q

What is the heel height adjustability limit?

A

3/8”

63
Q

Desribe why there tends to be anterior distal and posterior proximal forces upon heel stroke?

A

Because the socket has a tendency to tip forward and the knee is trying to go forward as well causing pressure

64
Q

What does the heel durometer indicate?

A

The Density of the material on the heel

65
Q

What is the heel height adjustability limit?

A

3/8”

66
Q

If the heel is too high what tends to happen? too low?

A

the knee will give out

the knee will hyperextend

67
Q

If the heel is too high what tends to happen? too low?

A

the knee will give out

the knee will hyperextend

68
Q

It is desirable to have varum at the knee during midstance. Will insetting or outsetting the foot create a varus moment?

A

Insetting the foot will create a varus moment.

Outsetting the foot will create a valgus moment (undesirable)

69
Q

If the foot is outset too much where will the pressures be in the socket?

A

Lateral distal

Medial proximal

70
Q

Do runners want a short or long toe lever?

A

long

71
Q

What is the desired ER of the prosthetic foot?

A

5-7 degrees for cosmetic purposes

72
Q

The more the foot is ER the ______ the toe lever becomes

A

shorter

73
Q

Does a soft or firm heel produce a shorter heel lever?

A

soft

74
Q

The softer the heel lever the _____ stability there is at the knee

A

more

75
Q

Does a soft heel promote knee flexion or extension?

A

extension

76
Q

Does a soft or firm heel produce a longer heel lever?

A

firm

77
Q

The firmer the heel lever the _____ stability there is at the knee

A

less

78
Q

What is the advantage of having a firm heel/longer heel lever?

A

It preserves more momentum and creates a better first (heel) rocker

79
Q

List 6 things that create knee flexion

A
  • firm heel
  • hard PF bumper
  • dorsflexing the foot
  • anterior tilting of the socket
  • sliding the foot posteriorly
  • higher heels

735: Orthotics and Prosthetics (14 decks)

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