Lever Arms, Rockers, and GRF's Flashcards
What are lever arms?
rigid structures through which a force can be applied to produce rotational motion about a fixed radius
How are lever arms determined?
By the perpendicular distance between the action of the vector (GRF) and the center of joint rotation
Define ground reaction force (GRF)
the force exerted by the ground on a body in contact with it
The rotational potential of the forces that act on a joint is called _____.
torque
Torque (M) = ______ x ______
amount of force (F) x lever arm (L)
The ground reaction force vector is the _____ load-bearing line, which takes into account the forces acting in all 3 planes.
mean
From initial contact through loading response there is a ____flexion moment. Explain why…
plantar
Because the force vector is behind the ankle
From midstance through toe-off there is a ____flexion moment. Explain why…
dorsiflexion
Because the GRF vector moves from behind the hell towards the forefoot
Orthotists describe _____ transitional periods, or rockers, during stance phase of walking as the body progresses forward over the foot.
three
Describe what happens during the first rocker
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
Where is the fulcrum at during the first rocker?
the heel
What muscles are active during the first rocker?
eccentric contraction of the quadriceps and anterior tibialis prevents “foot slap” and protects the knee as GFR is translated upward toward the knee
During the first rocker the foot ____ with flattening of medial arch, and thehind foot is positioned in ____ to allow absorption
pronates
valgus
What are 3 situations in which the first rocker is lost?
- heel pain (plantar fasciitis, bone spur, etc.)
- fixed equinus (foot lacks dorsiflexion, toe walkers)
- true or apparent Lower Limb Deficiency
Describe what happens during the second rocker
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
What muscles are active during the second rocker?
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
During the second rocker there is maximal _____ of the foot
pronation
Describe what happens during the third rocker
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
During the third rocker the foot moves into _____ and the heel is positioned in _____.
supination
varus
What muscle locks the midfoot during the third rocker so that the foot can act as a rigid lever?
tibialis posterior
What are 3 situations in which the third rocker is lost?
- painful forefoot (Hallux valgus/hallux rigidus)
- excessively stiff toe of prosthesis
- loss of PF (neuromuscular, stiff hindfoot, ruptured Transverse Arch)
In summary:
1st Rocker Phase occurs during _______
2nd Rocker Phase occurs during _______
3rd Rocker Phase occurs during _______
Heel Strike
Stance Phase
Toe Off
What are 4 functions of prosthetic feet?
- 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)
What are 2 things prosthetic feet may not be able to eliminate?
- a loss of plantar flexion during pre-swing
- a loss of dorsiflexion during swing phase
A soft heel = _____ heel lever which tends to increased stability at the knee
shorter
A soft heel allows for _____ foot flat
quick
easy PF movement
A firm heel = _____ heel lever which tends to decreased stability at the knee
longer
Although a longer heel lever leads to instability at the knee during the loading response it also has benefits, what are they?
It preserves more momentum and creates a better first rocker (the heel “rocker”)
A firm heel allows for _____ foot flat
slow
slower PF movement
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
low
larger
In regards to toes, a rigid toe allows for easier _____, whereas a softer toe allows for easier ______.
push off
roll over
Where will the COP be in rigid toes?
at the end of the foot
Where will the COP be in soft toes?
near the MP joint
Rigid toes have a ____ toe lever
Soft toes have a ____ toe lever
long
short
Rigid toes have a ____ dorsiflexion moment
Soft toes have a ____ dorsiflexion moment
high
smaller
Rigid toes have a ____ knee extension moment
Soft toes have a ____ knee extension moment
high
lower
What are the 3 advantages of having a stiffer ankle?
- easier to stand without effort
- increases control
- more energy can be stored
Typically K1 level patients use a _____ ankle foot
solid
K2-K4 patients use a _____ or _____ ankle foot
single or multi-axial rollover
What are the 6 functions of prosthetic knees?
- 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
What is a good starting point in regards to knee types for a patient who can vary their cadence?
a fluid control knee
The _____ the heel lever of the prosthetic foot, the more it is encouraging knee flexion at loading response which requires increased quad control
longer
A foot that is too stiff can cause excessive knee ______.
hyperextension
Excessive plantar flexion can correlate with knee ______.
Excessive dorsiflexion can correlate with increased knee _____.
hyperextension
flexion
Stride length should be equal bilaterally and is usually __ cm in males and __ cm in females.
80
65
What are a few examples of pre-gait training drills?
- standing the parallel bars
- weight shifting
- SLS
What are 3 gait deviations observed without adequate single limb WB?
- Decrease stance time on prosthetic limb
- Decreased stride length on sound side
- Lateral trunk bending over prosthetic limb
Describe the protocol for prosthetic gait training (5 steps)
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
Amputees typically have ____ arm swing on prosthetic side
decreased
When initiating sidestepping, should you step to the sound or prosthetic side first?
sound side
What is normal cadence?
2.5 mph
Most amputees use the step-to technique when ascending/descending stairs, however what amputee types may be able to do them reciprocally?
BKs and some AKs
Why do ramps and hills tend to be difficult for amputees?
Due to a lack of adequate PF and DF
What can be defined as the tendency for a movement?
Moment
In order for there to be a flexion moment the GRF must be ______ to the knee
posterior (behind)
How is a flexion moment produced in regards to foot positioning?
by moving the foot behind the knee
In order for there to be a extension moment the GRF must be ______ to the knee
anterior (in front)
How is an extension moment produced in regards to foot positioning?
by moving the foot forward under the knee
Where should we place the foot in a BK amputee and why?
Behind the knee to promote knee flexion so they don’t hyperextend their knee and wreck their own knee ligaments/capsule
Where should we place the foot in a AK amputee and why?
Under the knee or slightly in front to promote knee extension to increase knee stability
What is the purpose of dorsiflexing the foot?
in promotes knee flexion which stops the knee from hyperextending
What is the heel height adjustability limit?
3/8”
Desribe why there tends to be anterior distal and posterior proximal forces upon heel stroke?
Because the socket has a tendency to tip forward and the knee is trying to go forward as well causing pressure
What does the heel durometer indicate?
The Density of the material on the heel
What is the heel height adjustability limit?
3/8”
If the heel is too high what tends to happen? too low?
the knee will give out
the knee will hyperextend
If the heel is too high what tends to happen? too low?
the knee will give out
the knee will hyperextend
It is desirable to have varum at the knee during midstance. Will insetting or outsetting the foot create a varus moment?
Insetting the foot will create a varus moment.
Outsetting the foot will create a valgus moment (undesirable)
If the foot is outset too much where will the pressures be in the socket?
Lateral distal
Medial proximal
Do runners want a short or long toe lever?
long
What is the desired ER of the prosthetic foot?
5-7 degrees for cosmetic purposes
The more the foot is ER the ______ the toe lever becomes
shorter
Does a soft or firm heel produce a shorter heel lever?
soft
The softer the heel lever the _____ stability there is at the knee
more
Does a soft heel promote knee flexion or extension?
extension
Does a soft or firm heel produce a longer heel lever?
firm
The firmer the heel lever the _____ stability there is at the knee
less
What is the advantage of having a firm heel/longer heel lever?
It preserves more momentum and creates a better first (heel) rocker
List 6 things that create knee flexion
- firm heel
- hard PF bumper
- dorsflexing the foot
- anterior tilting of the socket
- sliding the foot posteriorly
- higher heels
