weightbearing in a prosthetic socket should be distributed where?
pressure tolerance areas
list pressure tolerance areas for transtibial prosthesis
- patellar tendon
- posterior distal aspect of residual limb
- popliteal fossa
- lateral shaft of fibula and tibial flares
Avoid putting pressure on ______ areas
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
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