Biomechanics of Prosthetic Use Flashcards
weightbearing in a prosthetic socket should be distributed where?
pressure tolerance areas
list pressure tolerance areas for transtibial prosthesis
- patellar tendon
- pretibials
- posterior distal aspect of residual limb
- popliteal fossa
- lateral shaft of fibula and tibial flares
Avoid putting pressure on ______ areas
bony
define bench alignment
how the prosthesis is set up/factory setup
in order to have M/L stabilization for transtibial prosthesis, what occurs during bench alignment?
attempt to replicate the normally occuring varus at the knee
by placing foot 1/2 inch medial to center
why should we want to replicate the varus at the knee for a transtibial prosthesis?
if the residual limb moves into valgus positoin in the socket it can result in pressure at the fibular head and peroneal nerve
how is A/P stabilization achieved in a transtibial prosthesis?
- place the socket in 5º flexion to enhance patellar tendon bearing (PTB)
- place foot slightly posterior to center of socket
describe 2 incorrect placements for transtibial prosthesis
- too far anterior → excessive anteroproximal and prosteriodistal pressure
- too far posterior → hyperflexion at the knee with excessive posterioproximal and anteriodistal pressure
how can you correct a TT foot outset?
translate the socket laterally or translate the foot medially
where would pressure from the socket be most felt in a TT foot oustet position?
(foot will be more lateral)
lateral superior lip of socket (proximal lateral)
and medial base (distal medial) of the socket
how can you correct a TT foot inset?
translate foot laterally or translate socket medially
where would pressure from the socket be most felt in a TT foot inset?
superior medial lip of socket
and lateral inferior edge of socket
having a TT socket anterior is the same as saying what?
the foot is too far posterior
where would pressure be applied the most on the socket in a TT socket anterior?
superior posteriorly behind the “knee”
base anterior portion
what 3 things should be kept in mind when considering transfemoral amputees biomechanics?
- minimize rotation of socket
- M/L stability
- sagittal plane stability
why is minimizing rotation of the socket a unique issue for a transfemoral prosthesis?
a transfemoral prosthesis is more like a round cylinder on a round peg and is very fleshy which can move a lot more than a TT which is more like a rectangle and gets good purchase of the prosthesis on the limb and doesn’t rotate a lot due to the bony angles
how can you minimize rotation of the socket in TFA?
- maintain pelvis position in a posterior tilt on posterior rim
- incorporate ischial/gluteal weightbearing
- adductor longus tendon housed in a groove
what 4 points will allow greater M/L stability in a TF prosthesis?
- need good lateral wall support (often make it slanted)
- provide abductor contact with the socket
- points of force in proximomedial direction and distolateral direction to prevent lateral shifting in socket
- center of heel under or slightly lateral to ischial tuberosity to promote slight valgus
why would we want to promote valgus in a TF prosthesis?
aids in M/L stabilization
promotes a Trendenlberg like gait and takes pressure off the medial socket/groin region
describe 2 incorrect foot placements for TF prosthesis
- foot too far medial (most likely) → excessive pressure in groin and distolateral
- foot too far lateral → excessive pressure proximolateral and distomedial
how is sagital plane stability achieved in a TF prosthesis?
GRF must remain anterior to the knee joint
this is achieved by having 5º flexion built into the socket (at the hip)
this enhances glute firing (and efficiency) and helps avoid hyperlordosis
define static checkout
looking for basic fit principles in a prosthesis
define dynamic checkout
assessing prosthesis during gait
list things included in a static checkout
- soles of feet are flat
- socket fits well
- user comfortable
- is suspension adequate?
- ensure bony landmarks are level (bilaterally)
- vertical pylon in stance
- minimize tissue rolls
- gapping between leg and socket
- does residuum have distal contact? (think plato)
- normal heel center spacing
- is the knee stable?
Define end-bearing socket
when the residuum bears weight at the distal aspect
define suspension
the means of holding the socket on the residuum
list pressure sensitive areas in a TT socket
- cut ends of the bones
- tibial crest and tuberosity
- fibular head
- tibial condyles
- distal hamstring tendons
List 2 socket designs used in TTA
- PTB - patellar tendon bearing
- TSB - total surface bearing
what is a TSB (total surface bearing) socket?
the entire limb contacts the socket, weight bearing is biased to pressure tolerant areas.
In a TSB socket there is nonspecific loading with minimal bony reliefs
usually use a gel liner
list the 2 methods used to measure someone for a socket
- casting (older method)
- computerized scan CAD/CAM of person’s limb
describe the bench alignment parameters for a TT socket
- foot set 1/2 inch medial to center of socket
- foot set slight posterior to center of socket
- heel height about 1/2 inch
describe the bench alignment parameters for TF socket
- center of heel under/slightly lateral to ishial tuberosity
- 5º of flexion built into socket at the hip
what factors help determine the type of suspension system used in a prosthetic?
based on the patient’s:
- residual limb
- comfort
- security
- hygiene
- function
There are many types of suspension systems, list a few of them
- supracondylar cuff
- suprapatellar/supracondylar
- suspension sleeve
- silicone/gel liners, 3S, Pin and Lock, Shuttle Lock
- Suction socket
- Elevated vacuum
- Tether strap
- Thigh corset
- Osseous Integration
describe a vacuum suspension system
a sleeve creates a seal around the top edge of the socket, then a pump and exhaust valve remove virutally all air between the socket and the liner as you wear them. The system regulates the vacuum level within a defined range.
This system enhances how well the socket adheres to your limb, which reduces shear, regulates limb volume changes, and improves circulation in your limb
describe a shuttle lock suspension system
a padded liner with a pin at the end is used
the pin is inserted into a shuttle lock built into the bottom of the socket. (variation of this system is the laynard/tether system)
Describe a suction suspension system
consists of a soft liner, one-way valve and a sealing sleeve.
insert the liner-covered limb into the socket and apply body weight as you stand to expel excess air through the valve
suction provides even adhesion to the entire interior surface of the socket for security, stability and reduced friction and shear
what are the pros/cons of suspension sleeve?
Pro → ease of use
Con → pistoning, bulky
what are the pros/cons of a pin system?
pros → ease of use, less bulk, accomodation of volume changes
cons → distal drawing
what are the pros/cons of a suction suspension system?
pro → more responsive
cons → harder to accomodate volume changes, loss of suction
what are the pros/cons of a vacuum suspension system?
pros → more responsive, secure suspension, can help maintain volume
cons → volume change accomodation, need air tight seal
what are the pros/cons of a tether suspension system?
pros → ease of use, accomodation of volume changes
cons → less responsive, unwanted movement
how can a heavy prosthetic foot impact gait?
can produce a pendulum effect resulting in greater fatigue in the leg
list the 2 categories prosthetic feet can fall under
- dynamic response → return energy to user to enhance gait
- nondynamic response
In a TT, the proximal portion of the tibia will follow the _________ while the distal end __________
proximal → head, arms and trunk
distal → translates in the oppposite direction
what gait deviations can be observed in TT during inital contact?
- excessive knee extension
- occurs if user is afraid to bend knee
- occurs if socket is placed too far posterior
- heel bumper may be too soft
- knee instability/excessive knee flexion
- occurs if socket is set too far anterior
- occurs if heel cushion is too hard
- occurs excessive DF of foot
what gait deviations can be observed in a TTA during midstance?
- raising or dropping of hip
- seen if prosthesis is too long/short
- narrow-based gait
- foot is too far inset
- lateral-leaning pylon
- glute medius weakness
- might see compensated/uncompensated Trendelenburg gait
- wide-based gait
- foot set too far laterally
- medialy leaning pylon
- sig sway of trunk to ipsilateral side during stance phase bilaterally
- pt fear can cause wide BOS
what gait deviations can be observed in TTA during terminal stance of gait?
- knee instability (drop off)
- socket is set too far anterior relative to foot
- vaulting
- seen if prosthesis is too long
- seen if knee is held in ext too long (can be seen if prosthesis is placed too far posterior relative to foot)
what gait deviations can be observed in TTA during swing phase of gait?
- loss of suspension/pistoning
- prosthesis begins to slide off
- can lead to tripping
- uneven step length
- usually noted as a longer step length on prosthetic side = shorter stance phase on prosthetic side
- circumduction
what gait deviations can be observed in TFA during intial contact to midstance?
- terminal impact
- audible sound as user forces knee into extension, usually b/c of insecurity/inadequate knee friction
- foot slap
- PF bumper is too soft
- if user forces heel down too strongly into ground to simulate PF
- knee instability
- can lead to falls
- knee axis is too far anterior or socket is placed too far posterior → causes a knee flexor moment
- hard heel cushion or lack of hip extension at heel strike can also cause this
what gait deviations can be observed in TFA during midstance?
- lateral trunk bending
- inadequate contact between residuum and lateral wall of socket
- medial wall of socket could be impinging on groin
- abducted gait
- foot/leg is outset thus widening BOS
- prosthesis is too long
- trunk extension
- user must hyperextend lumbar spine to extend hip when socket doesn’t have enough hip flexion built in
what gait deviations can be observed in TFA during late stance phase?
- drop off/knee instability
- seen if there is a loss of anterior support caused by a short keel or if the socket is posterior to the knee axis
what gait deviations can be observed in TFA during swing phase?
- circumduction
- vaulting
- pistoning
- whips
- can be seen M/L and is named according to direction in which the prosthetic heel moves at heel off
- usually caused by improperly aligned knee bolt
- excessive heel rise
- due to insuffienct knee friction in prosthetic knee
T/F: gait is less metabolically costly in amputees due to prosthetics doing most of the work
FALSE
it is never as efficient as able-bodied walking
increased energy expenditure during amputee gait
List some outcome assessment tools that help predict and quantify return to function in amputees
- Plus-M (prosthetic limb user survery of mobility)
- ABC (assesses balance confidence)
- TAPES (trinity amputation and prosthesis experience scale)
- AMP (amputee mobility predictor)
- BAMP
- CHAMP
