Lever Arm, Rockers, GRF Flashcards
1
Q
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A
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2
Q
How does foot length affect torque and energy return in prosthetics?
A
- 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.
3
Q
What is torque in the context of prosthetic gait?
A
- 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.
4
Q
Describe the impact of lever arm length on amputee gait.
Think heel & toe lever
A
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).
5
Q
( ? ) is the mean load-bearing line, representing forces acting in all three planes during gait.
A
Ground reaction force (GRF) is the mean load-bearing line, representing forces acting in all three planes during gait.
6
Q
What is the GRF vector position at initial contact?
A
- 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
7
Q
Describe the GRF vector position during loading response.
A
- 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.
8
Q
How does the GRF change during mid-stance?
A
- 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.
9
Q
Explain the GRF during terminal stance.
A
The GRF is anterior to the ankle (promoting dorsiflexion) and posterior to the hip (promoting extension).
10
Q
What occurs during the pre-swing phase in terms of GRF?
A
- 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.
11
Q
How do levers and moments impact amputee gait?
A
- 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).
12
Q
What is the effect of dorsiflexion and plantarflexion at the foot on knee movement?
A
- 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.
13
Q
How does heel height affect knee position in prosthetic users?
A
- 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.
14
Q
What are the three transitional rocker periods during stance phase?
A
- 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.
15
Q
Describe the first rocker phase and its significance.
first rocker lost when…
A
- 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.
16
Q
What replaces muscle control in prosthetics during the first rocker?
A
- Soft Heel/Short Heel Lever: Slows plantarflexion, promoting knee extension and stability.
- Firm Heel/Long Heel Lever: Speeds up plantarflexion, encouraging knee flexion but increasing instability.
- Prosthetic Impact: Adjustments to heel durometer and lever length ensure controlled weight acceptance and proper knee mechanics during the first rocker phase.
17
Q
Explain the second rocker phase.
A
- 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.
18
Q
How is the second rocker controlled in prosthetic users?
A
- 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.
19
Q
Describe the third rocker phase.
3rd rocker lost when…
A
- 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).
20
Q
What four factors influence the ease of rolling over vs. pushing off in prosthetics?
A
- 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.
21
Q
How does heel lever length impact knee movement during loading response?
A
- Longer HEEL Lever: Encourages knee flexion during loading response, requiring stronger muscular control for stability.
- Shorter HEEL Lever: Promotes knee extension, creating greater stability but reducing momentum.
- Firm Heel (Longer Lever): Preserves momentum but increases potential instability at the knee.
- Soft Heel (Shorter Lever): Enhances stability by promoting knee extension but limits energy efficiency.
22
Q
What is the effect of toe lever length on energy return and knee movement?
A
- Longer Toe Lever: Increases energy return but makes knee flexion harder, requiring more effort to bend.
- Shorter Toe Lever: Reduces energy return but eases knee flexion, simplifying forward progression.
- Stiffer Forefoot: Improves energy return but resists knee bending.
- Softer Forefoot: Facilitates rolling over and promotes knee flexion but decreases energy return.
23
Q
What factors impact knee stability in prosthetic gait?
A
- Heel Lever Length:
- Longer levers encourage knee flexion
- Shorter levers promote knee extension and stability
- Foot Position:
- Foot set backward promotes knee flexion
- Foot set forward promotes knee extension → stability
- Foot Dorsiflexion/Plantarflexion:
- Dorsiflexion increases knee flexion moments
- Plantarflexion increases knee extension moments → stability
- Prosthetic Foot Stiffness:
- Stiffer heels increase instability but preserve momentum
- Softer heels enhance stability by limiting knee flexion.
- User Strength:
- Stronger muscles can compensate for instability caused by longer or stiffer levers.
24
Q
How does heel durometer affect prosthetic gait?
A
Soft Heel:
- Slows plantarflexion, promoting knee extension and enhancing stability.
- Useful for individuals needing increased safety (e.g., K1/K2 users).
Firm Heel:
- Speeds plantarflexion, promoting knee flexion and preserving momentum.
- Provides better energy return but increases instability, requiring stronger muscle control.
Clinical Relevance:
- Heel durometer adjustments optimize gait efficiency and stability based on the user’s strength and activity level.
25
What is the impact of foot position on knee movement?
* **Foot Positioned Backward** (Relative to the Knee): Shifts the GRF behind the knee, promoting knee flexion.
* **Foot Positioned Forward** (Relative to the Knee): Shifts the GRF in front of the knee, promoting knee extension.
* **Dorsiflexion of the Foot**: Increases knee flexion moments by moving the GRF posteriorly.
* **Plantarflexion of the Foot**: Increases knee extension moments by moving the GRF anteriorly.
26
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.
27
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.
28
How does the ankle's stiffness affect mid-stance?
**Stiffer Ankle**:
* Provides more resistance during tibial progression, increasing stability.
* Can make rolling over harder, potentially slowing forward momentum.
**More Flexible Ankle**:
* Allows tibia to progress forward more easily, promoting smoother gait.
* May feel unstable if too flexible, giving a sensation of falling forward.
**Clinical Relevance**:
* Ankle stiffness is adjusted to balance stability and forward progression based on the user’s strength and activity level.
29
What is the purpose of split toe designs in prosthetic feet?
* **Mimics Natural Foot Function**: Allows inversion and eversion to improve balance and adaptability.
* **Shock Absorption**: Enhances shock absorption during midstance by accommodating uneven surfaces.
* **Stability**: Provides lateral stability by allowing controlled movement in the transverse plane.
* **Forward Progression**: Supports smooth tibial progression during the second rocker phase.
30
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.
## Footnote
* S's go together
* Hard toes & long toes
31
What is the relationship between heel lever stiffness and amputee safety?
Safer for users with weaker musculature to have shorter heel levers, as they require less muscular effort.
32
How does rocker function affect energy return?
* **First Rocker**: Influences shock absorption and knee stability; minimal impact on energy return.
* **Second Rocker**: Facilitates forward tibial progression; efficient transition improves momentum for energy return.
* **Third Rocker**: Primary contributor to energy return; stiff/long toe levers enhance push-off, while soft/short levers reduce energy return.
* **Prosthetic Adaptation**: Proper rocker function balances smooth progression and energy efficiency, tailored to user needs and activity levels.
33
Why is socket alignment crucial for effective gait?
* **Prevents Hyperextension**: Flexion alignment (~5°) prevents excessive knee hyperextension, protecting ligaments and joint capsules.
* **Optimizes GRF**: Proper socket alignment positions the GRF appropriately to promote knee stability or mobility as needed.
* **Improves Weight Distribution**: Aligns the patellar tendon for even weight bearing and reduces pressure points.
* **Enhances Gait Efficiency**: Promotes smooth transitions through rockers, reducing compensations and energy expenditure.
* **Prevents Malalignment Issues**: Misalignment (e.g., excessive adduction/abduction) can cause varus or valgus knee stresses, impairing gait mechanics.
## Footnote
* Proper alignment ensures correct GRF application, promoting efficient and safe ambulation.
34
What are the key considerations for integrating prosthetic knees and feet?
* **Heel Lever Length**: Longer levers encourage knee flexion, requiring strong muscular control; shorter levers promote knee extension for stability.
* **Toe Lever Stiffness**: Stiffer toes improve energy return but resist knee flexion; softer toes facilitate knee bending but reduce energy efficiency.
* **Knee Stance Stability**: Knees without stance stability require shorter heel levers for safety, while stance-controlled knees can handle stiffer heels.
* **Activity Level**: Components are tailored to the user’s functional level (K1–K4), balancing stability and energy return.
* **Alignment**: Proper positioning ensures GRF alignment for optimal knee and foot interaction, supporting efficient and safe gait.
