Lever Arm, Rockers, GRF Flashcards
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How does foot length affect torque and energy return in prosthetics?
- Longer Foot:
- Increases torque and energy return by acting as a stiffer lever.
- Requires more muscular effort to control and makes rolling over harder.
- Shorter Foot:
- Reduces torque and energy return but is easier to roll over.
- Lowers muscular demands, improving ease of mobility.
- Balance: Foot length is tailored to the user’s activity level, strength, and stability needs.
What is torque in the context of prosthetic gait?
- Torque Definition: The rotational potential of forces acting on a joint.
- Prosthetic Relevance: Longer foot levers increase torque/energy return but require more muscular effort to control.
- Impact on Gait: Excessive torque from a stiff or long lever can make rolling over difficult and increase energy demand.
Describe the impact of lever arm length on amputee gait.
Think heel & toe lever
Long Lever Arm:
- Acts stiffer, providing more energy return but requires greater muscular effort.
- Harder to roll over, promoting knee extension and stability but limiting mobility.
Short Lever Arm:
- Easier to roll over, reducing muscular demand and promoting knee flexion.
Provides less energy return, potentially leading to a less efficient gait.
Balance of Needs: Lever arm length is adjusted based on the user’s activity level and stability requirements (e.g., K1-K4).
( ? ) is the mean load-bearing line, representing forces acting in all three planes during gait.
Ground reaction force (GRF) is the mean load-bearing line, representing forces acting in all three planes during gait.
What is the GRF vector position at initial contact?
- posterior to ankle → promoting plantarflexion → by eccentric T-anterior and long toe extensor
- anterior to knee → promoting extension → by contraction of quad and eccentric hamstring lingering from terminal swing
- anterior to hip → promoting flexion → glutes & hamstring working eccentrically to fight flexion tendency
Describe the GRF vector position during loading response.
- Ankle: GRF is posterior to the ankle → creating a plantarflexion moment.
- Knee: GRF is posterior to the knee → promoting a flexion moment
- Hip: GRF is anterior to the hip → creating a flexion moment
- These positions require eccentric control from the tibialis anterior (ankle), quadriceps (knee), and hip extensors (glutes and hamstrings) to maintain stability and control.
How does the GRF change during mid-stance?
- Ankle: GRF moves anterior to the ankle → promoting a dorsiflexion moment
- Knee: GRF shifts to neutral or anterior to the knee → promoting passive knee extension.
- Hip: GRF moves posterior to the hip → promoting an extension moment.
- Impact on Muscles: Eccentric contraction of the gastroc-soleus controls forward tibial movement, while hip extensors gradually decrease activity.
Explain the GRF during terminal stance.
The GRF is anterior to the ankle (promoting dorsiflexion) and posterior to the hip (promoting extension).
What occurs during the pre-swing phase in terms of GRF?
- Ankle: GRF remains anterior to the ankle → brief concentric gastroc-soleus activity occurs early, then shuts off.
- Knee: GRF shifts posterior to the knee → promoting passive knee flexion.
- Hip: GRF remains posterior to the hip → promoting extension → rectus femoris and adductor longus initiate hip flexion.
- Function: This phase transitions weight off the limb, preparing it for swing.
How do levers and moments impact amputee gait?
- Lever Length:
- Longer foot levers → Increase stiffness and energy return but make rolling over harder
- Shorter levers → Ease progression but reduce energy return
- GRF Alignment: Foot positioning alters GRF moments
- Forward promotes knee extension
- Backward promotes knee flexion
- Moments:
- Dorsiflexion increases knee flexion moments
- Plantarflexion increases knee extension moments
- Stability vs. Mobility:
- Longer or stiffer levers require more muscular control, influencing safety and efficiency during gait.
- Individual Needs:
- Prosthetic adjustments are tailored based on activity level (e.g., K1 for stability vs. K3/K4 for energy return).
What is the effect of dorsiflexion and plantarflexion at the foot on knee movement?
- Dorsiflexion: Increases knee flexion moments by moving the GRF posterior to the knee, requiring greater control to prevent collapse.
- Plantarflexion: Increases knee extension moments by moving the GRF anterior to the knee, promoting stability but reducing mobility.
How does heel height affect knee position in prosthetic users?
- Raising the heel promotes knee flexion
- Lowering it promotes knee extension
Raising the Heel (like wearing high heels):
- Tilts the prosthetic foot forward.
- Pushes the weight toward the toe.
- The knee flexes (bends) to balance the forward shift.
Lowering the Heel (like wearing flat shoes):
- Tilts the prosthetic foot backward.
- Pushes the weight toward the heel.
- The knee extends (straightens) to balance the backward shift.
Key Visual - Walking Uphill vs. Downhill
- Walking Uphill (like a raised heel): Your knees bend more to help keep your balance.
- Walking Downhill (like a lowered heel): Your knees straighten to stabilize you as you shift your weight backward.
What are the three transitional rocker periods during stance phase?
- 1st rocker: controlled lowering of forefoot
- 2nd rocker: forward progression of tibia,
- 3rd rocker: transition to toe-off.
“Heel, Roll, Push”
1st) Heel:
- Think of the first rocker as when your heel lowers and starts the motion.
- Controlled lowering of the forefoot.
2nd) Roll:
- The second rocker is the rolling forward of your shin (tibia) over your planted foot.
- Forward progression of the tibia.
3rd) Push:
- The third rocker is the push-off phase where your toes propel you forward.
- Transition to toe-off.
Describe the first rocker phase and its significance.
first rocker lost when…
- First Rocker (Heel Rocker): Occurs from initial contact to loading response as the foot transitions from neutral to plantarflexion.
- Ankle Motion: Controlled lowering of the forefoot occurs, using the heel as a fulcrum.
- Muscle Activity: Eccentric contraction of the tibialis anterior controls plantarflexion and prevents foot slap.
- Knee Protection: Quadriceps eccentrically control knee flexion to absorb shock and stabilize the limb.
- Prosthetic Adaptation: Heel durometer and lever length determine the rate of plantarflexion, replacing muscle control.
- Significance: Enables smooth weight acceptance and protects the knee from excessive flexion or extension forces.
Explain the second rocker phase.
- Second Rocker (Ankle Rocker): Occurs during midstance as the tibia rotates forward over the fixed foot.
- Ankle Motion: Moves from plantarflexion to dorsiflexion as the GRF shifts forward.
- Muscle Control: Eccentric contraction of the gastrocnemius and soleus slows tibial progression.
- Prosthetic Adaptation: Hip and thigh muscles replace ankle control, with prosthetic foot stiffness modulating forward progression.
- Foot Mechanics: Keel stiffness and split-toe designs mimic natural shock absorption and stability.
How is the second rocker controlled in prosthetic users?
- Hip and Thigh Muscles: Control forward tibial progression, compensating for absent gastroc-soleus eccentric control.
- Prosthetic Foot Design: Toe length and stiffness modulate tibial advancement; softer toes ease progression, stiffer toes slow it down.
- Keel Stiffness: Replaces natural foot flexibility to manage forward momentum.
- User Compensation: Hip and pelvis adjustments provide additional control over trunk and tibia movement.
Describe the third rocker phase.
3rd rocker lost when…
- Third Rocker (Toe Rocker): Occurs during terminal stance and pre-swing as the heel lifts off the ground.
- Forefoot Function: Forefoot transitions from a mobile adapter to a rigid lever for effective push-off.
- Joint Motion: Dorsiflexion occurs at the metatarsophalangeal joints as weight rolls over the forefoot.
- Muscle Activity: Concentric contraction of the gastrocnemius-soleus complex propels the body forward.
- Prosthetic Adaptation: Toe stiffness and length impact ease of rolling over (soft toes/short lever) or energy return (stiff toes/long lever).
What four factors influence the ease of rolling over vs. pushing off in prosthetics?
- Toe Stiffness: Soft toes ease rolling over but reduce energy return; firm toes ease pushing off and increase energy return.
- Toe Length: Shorter toes make rolling over easier but decrease energy return; longer toes make rolling over harder but improve energy return.
- Prosthetic Foot Design: Features like keel stiffness and split-toe designs impact flexibility and ease of transition.
- User’s Strength: Stronger users may handle stiffer toes/longer levers better, enabling efficient push-off.
How does socket flexion affect weight-bearing?
- Increased Socket Flexion:
- Distributes weight-bearing over a larger area of the residual limb, reducing localized pressure.
- Enhances comfort and reduces the risk of skin breakdown.
- Promotes Anterior Weight Bearing:
- Shifts weight to the patellar tendon, a key load-tolerant area, optimizing prosthetic support.
- Improves Gait Efficiency:
- Encourages smooth knee flexion during gait, reducing compensatory patterns.
- Prevents Hyperextension:
- Limits excessive knee extension, protecting ligaments and joint structures.
What alignment considerations are made in the transverse plane?
- Foot Abduction (5–7 Degrees Normal): Maintains natural gait; excessive abduction shortens the toe lever.
- Toe-Out Position: Shortens the toe lever, easing rolling over but reducing energy return.
- Patellar Tendon Alignment: Ensures level positioning to optimize weight distribution and avoid imbalances.
How do prosthetic users adapt during fast walking or running?
- Third Rocker Adaptation: Active contraction of the gastrocnemius-soleus complex propels the limb into swing phase.
- In a prosthetic user this is affected by the stiffness of the toes/length of the toes
- Forefoot Stiffness: Stiff toe levers provide a rigid base for push-off, enhancing energy return during faster gait.
- Dynamic Components: High-activity prosthetic feet (e.g., split-toe designs, dynamic pylons) improve flexibility and energy storage for propulsion.
- Hip and Thigh Engagement: Increased reliance on proximal muscle strength compensates for lack of active ankle control.
- Momentum and Acceleration: Faster walking or running leverages forward momentum and efficient GRF alignment for propulsion.
- S’s go together
- Hard toes & long toes
