interfaces, socket design, suspension (11/5)

interface

material between socket & pt skin

purpose: suspension, skin protection, adjust socket fit (esp if RL vlume fluctuates)

socket may be rigid or flexible

goals of suspension

little to no mvmt btwn RL and socket

comfort w/o skin breakdown or irritation

no interference w/ knee flex in sitting (TT)

prosthetic remains secure for all of pt activities

suspension may be primary or ancillary (added for <security)

PTB socket

ant wall: pry WB, bisects patella and w/ indented “patellar tendon bar”

med/lat walls: knee stability, rise above proximal pole of patella

post wall: push RL onto ant wall—room for hamstring tendons, med side lower than lat

long RL: shorter post wall for full KF ROM

short RL: higher post wall to retain soft tissue in socket

total surface bearing

shape in transverse plane reflects cross section of limb (typically round)

fits snugly to disperse forces across all surfaces

gel liners help reduce shear, improve comfort

many current prostehtics in hybrid shape

transtibial suspension types

pin-lock

suction

sleeve

elevated vacuum

supracondylar, suprapatellar

cuff & waist belt/strap

pin lock suspension

most common form of TT suspension

silicone liner w/ attached distal pin

pin slides into hole in distal socket, locks in place

ridges on pin make audible “click”

fit can be adjusted w/ adding/removing socks

release w/ button on exterior of socket

mechanisms wear out over time

suction suspension

silicone liner seals into place, generates suction force between RL and socket

may have expulsion valve to continuously remove air, maintain - psi

more common in TF amputees

sleeve suspension

combo of silicone liner & ext sleeve made of latex/neoprene/similar

airtight seal btwn sleeve & liner

good cosmesis, min impact on KF

can be hot (incr perspiration, fit issues, skin irritation)

easily damaged, expensive to replace

liner & sleeve may be difficult for pts w/ UE dysfunction to don/doff properly

elevated vacuum

electric or manual/mechanical pump generates continuous - psi

works best w/ TSB socket

requires liner & sealing sleeve

supracondylar & suprapatellar suspension

proximal brim of socket extends over patella, medial & lateral femoral condyles

uses flexible inner socket made of foam

encourages slight KF

transtibial socket design

2 pry designs: PTB, TSB

both reduce WB through distal end of RL

PTB loads psi tolerant areas, TSB disperses psi across large surface area

off-load zones (psi intolerant)

sharp bony prominences: fib head, cut end of fib, tibial tubercle, tibial crest, patella

load zones (psi tolerant)

muscle bellies, broad/flat areas of bone & soft tissue: patellar tendon, ant tibial muscles, post muscles, femoral condyles, medial tibial flare, tibial shaft

sagittal plane alignment

modulates forces of WB & ant/post knee stability

socket is ~5 deg of flexion (prox end tilted ant compared to distal)=slight DF & KF, extra socket flexion needed to accommodate KF contracture

prostehtic foot position set based on heel height of shoe

change of footwear, inappropriate heel cushion stiffness→impacted KF/KE moment in stance

frontal plane alignment

modulates forces of WB & med/lat stability

socket in ~5 deg adduction

prosthetic foot directy under socket: vertical line transects heel, may be inset <½“

inset or outset impacts forces on RL (varus/valgus), comfort, energy cost

inset foot position impact

foot placed more medially on socket

varus force thru knee during stance

incr loading thru prox-med and distal-lat socket

can cause gapping of prox-lat socket, but also reduces pressure on fibular head

outset foot position impacts

foot placed more laterally on socket

valgus force thru knee during stance

incr loading thru distal-med & prox-lat socket

wider BOS

less energy efficient, may reduce pain & improve comfort for pts with short RL

transfemoral socket design

ischial containment, marlo anatomical socket, quadrilateral, subischial (L→R)

quadrilateral socket

square/rectangle shape

med-lat dimension bigger than ant-post

higher ant/lat wall: better stability, forces→post

post shelf: WB thru ischial tub & glutes

med wall: concavity to relieve add longus tendon

lateral wall: concavity to relieve greater troch

ischial containment socket

ischial tub & pubic ramus sit w/in socket

ant-post dimension larger & provides room for mm contract

high med walls limit lat displacement & mimics natural add angle of femur

TF socket considerations

limited evidence in research to guide decision making

general strategies: ischial containment for short, weak RL w/ lots of soft tissue/little muscle, quadrilateral for long/firm/strong RL, subischial for greater amount of hip ROM

quad socket: good AP stability in sagittal, limited ability to prevent femur from lateral drifting

ischial containment: forces directed sup & med to keep femur in add position & maintain level pelvis

TF alignment sagittal

mechanical knee jt needs to be ext in stance

CL step length should be normal

5 deg flexion in socket or 5 extra if pt has contracture: elongates hip ext to improve contractile force, reduces tendency to compensate for weak hip ext w/ lumbar lordosis

TF alignment frontal

socket fabricated in 5-7 deg of add

establishes normal angle of femur

lat wall of socket→med directed force for stability

elongate fibers of glute med to improve contractile force

foot position: plumb line from ischial tub should bisect heel; inset bc narrow BOS more energy efficient

sagittal plane factors impairing stability

weak hip exts, short RL, hip flex contracture, higher heel on shoe, knee unit set ant to wt line

frontal plane factors impairing stability

weak hip abd, short RL, hip abd contracture

transfemoral suspension

traditional pull-in suction

roll-on liners

total elastic suspension

silesian belt

pelvic belt

osseointegration

pull-in suction

req snuf prox fit, distal air expulsion valve to maintain - air psi, no air entry

don: liquid power/pull sock

benefits: comfort, cosmesis, good proprioception & prosthetic control

drawbacks: not for recent amp/fluctuating volume, high shear during donning, not good for fragile skin/scars/trigger points/adhesions, req good strength & control in RL and UEs

roll on liners

similar to use in transtibial prosthetics

liners made from silicone, urethane

distal air expulsion valve; suction maintained btwn liner & socket

benefits: easy to don/doff; liner contains soft tissue; can be used for short RL or limbs w/ scar/adhesions

drawbacks: liners not durable, must be replaced often; hygiene concerns

variations: pin lock, lanyard, elevated vacuum

total elastic suspension

elastic neoprene

distal sleeve attaches to socket & waist belt holds in place

may be used as sec suspension for athletes

benefits: appropriate for recent amp, OAs unable to use traditional suction/liners, pt with tender skin or adhesions

drawbacks: hot, unable to control RL rotation w/in socket

silesian belt

harness attaches to lat socket

belt wraps around waist/trunk

buckles on ant socket

benefits: relatively easy & lightweight

drawbacks: unable to fully control RL rotation w/in socket

pelvic belt

rigid single axis hip jt just sup/ant to greater troch

improve med-lat stability of prosthesis, reduce rotation

benefits: helpful for short RL; used pry w/ quad socket

drawbacks: heavy, longer fabrication time, uncomfy in sitting, maintenance, noise

osseointegration

surgically implanted metal pin connects direct to prostehsis w/o need for socket

benefits: No pistoning, direct WB thru femur, lightweight

pts req fewer prosthesis appointments for adjustment

drawbacks: complications range from mild infection to osteomyelitis, need for removal, possible bone loss or more prox amputation

in case of fall→incr forces thru femur

TF prosthetic goals

knee stability in stance phase

KF to ensure foot clearance in swing phase

smooth transitions btwn stance & swing

constant contact btwn socket & RL

min gait deviations=reduce energy cost w/ amb