Prosthetic Components and Biomechanics Flashcards
Aspects of patellar tendon-bearing socket
- loads patellar tendon and medial tibial flare
- off-loads tender boney areas
- low posterior trim line to allow for hamstring tendons
- relief for fibular head
Aspects of total surface-bearing socket?
- distributes weight bearing over entire surface of residual limb
- goal is uniform pressure and reducing shear forces
- difficult to make correctly
Aspects of quadrilateral socket?
- 4 walls that contain the thigh
- flat posterior shelf that is primary weight bearing surface for ischial tuberosity and glute muscles
- Anterior wall higher than posterior
Aspects of ischial containment socket
- covers the ischial tuberosity
- wider anterior > posterior than medial > lateral to resist extra femoral abduction
- high medial and posterior wall
Pros and Cons of lanyard suspension
Pros
- very secure
- consistent alignment
- does not take much space at bottom of socket
Cons
- visible from outside of socket
Pros and Cons of pin-lock suspension
Pros
- very secure
- mechanical connection
Cons
- can cause suction effect
- difficult to align if deaf or blind
- shuttle lock takes up space in socket
Pros and Cons of suction suspension
Pros
- good for blood flow
- very good suspension
- provides for fluctuating limb volume
Cons
- can wear out liners quickly
Pros and Cons of elevated vacuum suspension
Pros
- very comfortable for the user
- allows for limb volume fluctuations
Cons
- heavy
- must be charged
- extra component that takes up space at the end of the socket
What liner is typically used with pin-lock systems, soft and resistant to pressure, durable and good for everyday use?
silicone
What liners are good at absorbing pressures, used with vacuum and suction suspension systems?
polyurethane
What liners are good for low activity level and for total surface bearing sockets?
copolymer
When is the limb the largest in volume?
when the patient first wakes up in the morning
What type of foot is typically used with each K level?
K1 - SACH foot (rigid)
K2 - single axis or multi-axial
K3 - Multi-axial
K4 - hydraulic ankle, multiaxial, or crossover
Soft vs hard heal of SACH foot
soft - mimic PF and absorb impact more
hard - won’t absorb impact and makes the patient feel like they are in a neutral or DF state
What motions are permitted with a single axis foot?
Plantarflexion and dorsiflexion
What motions are permitted with multiaxial feet?
plantarflexion and dorsiflexion
inversion and eversion
What are the 2 goals of prosthetic knees?
- stance phase control
- swing phase control
What knee provides stance control through alignment, encouraging the ground reaction force to be _________ to the knee?
single axis and polycentric knee
- anterior force to the knee
What knee is the most stable stance control? How do the patients walk?
- manual locking knee
- patients will circumduct, vault, and hip hike to walk because limb is locked in extension while walking
What knee provides for swing phase control by dynamically adjusting swing speed to user’s gait speed? How does it control swing speed?
hydraulic and pneumatic knees
swing speed controlled through friction
What knee provides stance and swing phase control? How does it do that?
microprocessor knees
sensors measure joint angles, cadence, etc. to provide stable knee that is responsive
What are the pressure tolerant areas in patellar tendon bearing sockets/
- patellar tendon
- pretibials
- posterior distal aspect of residuum
- popliteal fossa, lateral shaft of fibula and tibial flares
What rule should you always remember for biomechanics with prosthetics?
head, arms, and trunk will follow where your leg goes
- proximal part of the socket goes in the direction of the head, arms, and trunk
Where does the mechanical axis run through in the lower limb? What moment is created at the knee?
- runs from center of femoral head to center of ankle - should cross the knee center
- creates varus moment at the knee
Where does the anatomical axis run through in the lower limb? What moment is created at the knee?
- runs through center of femoral shaft and then through tibia
- creates a valgus angle of the knee
Where should the foot be in transtibial during bench alignment? What moment does this create at the knee?
- 5 inch medial to center (medial/lateral stabilization)
- creates varus at the knee
Why do you want to avoid a valgus stress at the knee?
a valgus moment at the knee puts pressure in the fibular head which has the peroneal nerve behind it
Proximal part of the socket puts pressure on the ______ side of the knee and distal pressure on the _______ side of the residual limb
Proximal - medial
distal - lateral
A foot that is too far inset is the same as a socket that is what? What is this also called in reference to the socket?
too far outset
- AKA abducted socket
For anterior/posterior stabilization, where should the socket be placed to enhance PTB?
5 degrees of flexion - allows weight bearing through the patellar tendon
For anterior/posterior stabilization, where should the foot be placed? Why?
foot slightly posterior to center of socket
- puts the knee in a little bit of a flexor moment so you have more power b/c the quads are on slack
Where are the pressures if the foot is too far anterior in transtibial?
anterioproximal and posteriordistal pressure
Where are the pressures if the foot is too far posterior in transtibial?
hyperflexion at the knee with posterioproximal and anteriodistal pressures
What things are done to minimize rotation of the socket in transfemoral sockets?
- maintain pelvis in posterior tilt on posterior rim
- incorporate ischial/gluteal weightbearing
- adductor longus tendon housed in a groove to prevent breakdown and help block rotation
For transfemoral sockets and medial/lateral stability, you want points of force in __________ direction and ________ direction to prevent lateral shifting in socket
proximomedial and distolateral
For transfemoral sockets and medial/lateral stability, you want center of heel __________ to ischial tuberosity to promote slight ______
- under or slightly lateral
- promote valgus
In transfemoral, foot too far medial: excessive pressure in groin and ________
distolateral
In transfemoral, foot too far lateral: excessive pressure proximolateral and _________
distomedial
Floor reaction force must stay _______ to the knee joint. Why?
- anterior
- posterior pull will cause flexor moment at the knee leading to instability
How much flexion is built into the socket of transfemoral? Why?
- 5 degrees of flexion
- enhances firing of the gluteals to allow hip extension and passively extend the knee
- allows ability to extend the knee w/o lordosis to throw the hip forward and lock the knee out
