Lever Arms, Rockers & GRF Flashcards
How can you remember the 3 rockers?
HAM! Heel, ankle, metatarsals
What are the 3 transitional rocker periods and how it relates to stance phase?
- Heel: transition from swing into early stance, controlled lowering forefoot occurs, with fulcrum at heel
- Ankle: controlled forward progression of the tibia over foot occurs, with motion of talocrural joint of ankle
- Metatarsals: transition from stance toward swing occurs as heel rises, with DF of MTP joints
Describe 1st Rocker Phase
Heel Strike: During the first (heel) rocker, there is a 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. When motor control and muscle performance is efficient, eccentric contraction of the quadriceps and anterior tibialis prevents “foot slap” and protects the knee as GRF is translated upward toward the knee.
1st rocker is lost with:
- heel pain
- fixed equinus (foot lacks DF, toe walker)
- true or apparent LLD (lower limb discrepency)
What does the foot do during 1st rocker phase
I don’t know how else to ask this
Foot is lowered onto ground under control of eccentrically acting tibialis anterior
Foot pronates with flattening of medial arch, and hind foot in valgus to allow shoe absorption
Describe 2nd Rocker Phase
n the second (ankle) 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 mid-stance is completed. Eccentric contraction of the gastrocnemius and soleus muscles “puts on the brakes” to control the speed of the forward progression of the tibia over the fixed foot throughout mid-stance.
During 2nd Rocker-is it PF or DF happening?
Progressive DF of ankle allows tibia and COG to progress over foot
This was a quiz question
Describe 3rd Rocker phase
Toe Off
At the start of the third (toe) rocker, the forefoot has 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 body weight has to roll over the first metatarsophalangeal joint through push-off in terminal stance. During fast walking and running, acceleration occurs as active contraction of the gastrocnemius-soleus complex propels the foot and leg into swing phase.
3rd Rocker phase Description
Foot rotates over MT heads
Foot moves into supination, heel into varus
Tib Post locks midfoot so foot can act as rigid lever
Concentric contraction of triceps surae and FHL provides pushoff
3rd Rocker is lost with:
painful forefoot (hallux valgus/hallux rigidus) excessively stiff toe of prosthesis -Loss of PF
Function of Prosthetic feet
- provide controlled PF at Loading response
- provide easy movement from hindfoot to forefoot
- control large DF moment at Terminal stance to prevent collapse over ankle
What are movements that prosthetic feet have not been able to eliminate
A loss of PF during pre-swing and Loss of DF during swing phase
Soft heel=Short/Long heel lever=Stable/unstable at the knee
Soft heel=shorter heel lever=stability at the knee
Describe soft heel
Early Loading response more loading but still low easy PF movement of foot quick to foot flat quick shortening of heel lever=low PF movement
Firm Heel=long/short lever arm =more flexion/extension but potential for instability
Firm heel=longer lever arm= more flexion or ease of mobility but a potential for instability
Describe Firm Heel
Instability at the knee at loading response can occur due to longer heel lever however this longer heel lever preserves more momentum and creates a better first rocker (the heel “rocker”) Harder heels (firmer durometer of heel), a hard plantar flexor bumper, dorsiflexing the foot, anterior tilting of the socket, or sliding the foot back, or higher heels creates knee flexion
Lever arms are determined by what?
the perpendicular distance between the action of the vector and the center of joint rotation
The rotational potential of the forces that act on a joint is called ______.
Torque
Torque moments = ________ x ________
the product of the force; the lever arm
What is ground reaction force?
It is the mean load bearing line.
- It takes into consideration forces acting in all three planes
What is a moment?
Tendency for a movement
Where does the ground reaction force need to be?
Behind the knee
When you move the foot behind/posterior the knee, where does the ground reaction force move?
Moves to behind the knee = flexion tendency
When you move the foot in front of/anterior to the knee, where does the ground reaction force move?
Moves in front of the knee = extension tendency
In a BK, where do you want the ground reaction force to be in relation to the body? Why?
Behind the knee - to promote knee flexion, so they do not hyperextend & ruin knee capsule and/or ligaments
In a AK, where do you want the ground reaction force to be in relation to the body? Why?
In front of the knee - to promote extension so they are more stable
When your foot is dorsiflexed what happens to the ground reaction force/physiological movement?
The ground reaction force causes an increased knee flexion moment
What ankle movement stops hyperextension?
dorsiflexion
At heel strike the socket has a tendency to tip forward & the knee is trying to go forward, causing pressure where?
Anterior distal & Posterior proximal
What is the limit of heel height adjustability?
3/8 inch
What is the prosthetic foot size like compared to the patient’s sound size?
The prosthetic foot needs to be a 1/2 size smaller.
What is the term that describes the density of the material used for the foot prosthesis?
Heel durometer
What is the desired position of the pylon once the shoe is attached and the foot is on the floor?
Vertical
