BK Prosthetics Flashcards
Largest cause of LL amputation
Dysvascular (followed by congenital, trauma, and cancer)
Largest LL amputation population (level of amputation)
Toes/foot
Percent chance a person will have contralateral limb also amputated within 3-5 years
55%
5 yr mortality rate for persons w/dysvascualr disease after amputation
50%
‘Ideal’ limb length
12 cm distal to knee (lever arm)
23 proximal to floor (room for components)
Myodesis vs Myoplasty
Myodesis = muscle to bone (more stable) Myoplasty = antagonist muscle to agonist muscle
Most common TT surgical technique
Posterior flap method
Fibula transacted this amount above end of tibia
1-1.5cm
Anterior tib beveled 45°
TMR vs RPNI
TMR = nerve ending attached to intact muscle RPNI = nerve ending wrapped in muscle graft
Potential benefits of RPNI and TMR in lower limb
Decrease neuromas & phantom limb pain
Ertl procedure, advantages, indications
Bone bridge between tibia and fibula
Creates wider base for prosthetic fitting, stabilizes the distal bone interval
Young, healthy individuals, fibular instability
Concerns in post op stage
Knee flexion contractures
Volume changes
Protection
Early ambulation
Post op goals
Protect limb for healing
Preserve/improve strength
Prepare limb for prosthesis
Post op protective dressing options
Soft dressing Non removable rigid IPOP Removable rigid (RRD) Prefab prosthetic
Preferred choice of post op protective dressing and benefits
RRD
Reduce injury from falls Reduce knee flexion contracture Reduce edema Reduce healing time Reduce time to prosthetic fitting Reduce pain Inspection of incision
Post op edema management methods
Ace wrap
IPOP
Compression garment (shrinkers, compressogrip)
Pressure gradient for edema control
Pressure is high distally and less proximally (reduces distal to proximal)
Pros/cons of ace wrap
Good control and adjustment of compression if properly applied
Has to be reapplied every few hours
Pros/cons of shrinkers and recommended pressure amount
Class II 30-40 mmHg
Easy to don and wash
Higher cost, may require multiple sizes over time
Pros/cons of compressogrip
Customize size, low cost
Compression is NOT graded
What point after amputation can prosthetic fitting occur?
Staples/sutures removed
Wound healed
Volume stabilized*
Baseline anatomical landmark for length measurements
Midpatellar tendon
Which hamstring tendon attaches more distally?
Medial (Semitendinosus and semimembranosus)
Pressure tolerant areas of RL
Patellar tendon Medial tibial flare Pretibial muscles (ant. compartment) Gastrocsoleus Popliteal fossa Fibulae shaft Distal end*
Pressure intolerant areas of RL
Lateral tibial condyle/Gerdy’s tubercle Tibial crest Distal anterior tibia Fibulae head / common peroneal nerve Hamstring tendons
Function of socket
Contain, support, and protect RL
Rigid attachment to components
Energy/force transfer between pt and ground
Protect limb from damaging pressures / impact forces
Average surface area of TT RL
52 in^2
Force, pressure, and area relationship
Force applied over greater area reduces pressure
Potential result of lack of distal end contact
Verrucous Hyperplasia ‘wart like’ overgrowth
Edema->VH->cancer if untreated
Method to reduce verrucous hyperplasia
Total contact (distal end contact)
*DE contact, not DE weight bearing
PTB, PTBSC, PTBSC-SP, TSB stands for
Patellar tendon bearing
PTB supracondylar
PTBSC suprapatellar
Total surface bearing
Hybrid socket design combines what loading methods
PTB + TSB
Loading principle of PTB vs TSB
PTB = specific weight bearing (load pressure tolerant, relief for intolerant areas) with AP compression
TSB = pressure distributed equally across entire surface of RL
Describe AP force couple in PTB
High posterior brim counters the patellar bar
Posterior trim line should extend proximal to MPT level (~12mm, w/socket in appropriate flexion)
PTBSC suspension method and indication
Anatomical suspension over femoral condyles
ML knee instability (short RL, ligament laxity)
PTBSC SP suspension and indication
Anatomical suspension over femoral condyles
Knee hyperextension
If poor ROM and strength, consider joint/corset instead
Feature and function of PTBSC SP
High trim line over patella (1”) with quadriceps bar to resist knee hyperextension in late stance
Quad bar must be modified at correct angle and depth (~10°)
PTB indications
Limb has specific pressure/weight intolerant areas (atrophy, sensitive areas)
Anticipated volume changes
Donning, hygiene challenges (gel not recommended)
Previously satisfied user
Basic idea of hydrostatic theory
Soft tissues behave as an elastic solid with low stiffness when under load
TSB suspension
Skin fit or Gel liner
No voids crucial to maintain suction
Function of shank
Maintain spatial relationship (height and alignment) between socket and foot
Types of shank construction
Endoskeletal and exoskeletal
Exoskeletal design pros/cons
High strength, durability, less exposed componentry, can be fab’d for light or heavy duty use
Alignment is not adjustable, replacement is more difficult/costly
Endoskeletal design pros/cons
Modular, interchangeable components, alignment changes and adjustability, greater component selection
Higher strength requires heavier and more costly components, less durable, components are exposed
Common and standard pylon diameters
30mm (standard)
34mm
Protective cover coverage by Medicare
Medicare allows custom shaped foam cover for protection of components
Flexible outer protective surface (skin) considered not medically necessary - use stockings instead
Indications for protective cover
Protection of components (dust and debris, corrosive environmental agents, incontinence)
Function of foot
Transfer and absorb GRF
Absorb shock
Weight bearing stability
Progression through gait cycle
Prosthetic feet are described by
Material
Heel
Keel
Functional properties
Function of heel
Shock absorption in LR, knee stability
Varied by heel cushion, bumpers, hydraulic
Function of keel
Semi rigid lever arm to control advancement of limb over foot and support weight after MS
Keel stiffness based on
Weight and activity level
SACH function
Solid ankle cushioned heel
Heel compresses in LR for shock absorption and PF, keel deflects in late stance
Prosthetic heel compression simulated what normal mechanism
DF activity to control PF of ankle during LR
SACH pros/cons/indications
Low maintenance, low cost, varying heel heights available
Deterioration of material, no coronal ground compliance
Limited ambulators, children (durability/size), need for durability
Single Axis foot function
Passive PF/DF with bumpers for knee stability in LR by reducing knee flexion moment
When do anterior and posterior bumpers compress in gait / what type of resistance is provided
Posterior bumper is compressed in LR for PF resistance
Anterior bumper is compressed in late stance for DF resistance
Single axis foot pros/cons/indications
Promotes sagittal knee stability
More maintenance (moving parts)
Weak quads/poor control of knee flexion, limited ambulator (short distances at low speed)
Flexible keel foot function
Flexible keel allows FF inversion/eversion and smooth rollover to improve transition to same side in TS
Flexible keel foot pros/cons/indications
Smoother rollover, FF inversion/eversion (vs SACH)
Moderate increase in weight and cost (vs SACH)
More than limited ambulator - walk outside home but not at variable speeds
Multiaxial foot function
Passive motion in 2+ planes, may be additional feature on another type of foot
Multiaxial pros
Ankle PF (knee stability in LR) Ankle DF (softer rollover in TS) Ground compliance (uneven terrain) Absorption of rotational forces
Dynamic response / energy storage and return / flex foot / flex walk function
Spring keel (carbon/fiberglass) deflects under load (absorbs energy) and rebounds when unloaded (return) for subjective sense of push off
ESAR pros/indications
Reduced energy, reduced impact of cyclic vertical loading, lighter weight
At risk for overuse injury (contralateral), variable cadence (community ambulators)
Hydraulic ankle function
Single axis feature with adjustable hydraulic dampening of PF and DF
Often combined w/ESAR or flexible keel
Hydraulic ankle pros/cons
Variable resistance (dampens at high speeds), adjustable resistance
Increased weight and cost (vs single axis)
Torsion adapter function, advantages, indications
Transverse plane rotation w/resistance
Replaces loss of rotation from foot and ankle, reduces shear at limb-socket interface
Helpful for bilateral, specific activities/sports
Vertical shock absorber function, advantages, indications
Absorbs shock, may be individual component or part of a foot
Improves weight absorption at IC, reduces impact to at risk/damaged proximal joints
Activity specific/sports
Function of suspension
Hold prosthesis on RL
General categories of suspension
Anatomical
Mechanical
Atmospheric
Other (OI)
Types of anatomical suspension
Joints and corset
Waist belt and fork strap
Supracondylar
Supracondylar cuff
Describe joint and corset suspension
Mechanical joints and uprights attach socket to thigh lacer which can be tightened to help suspend and transfer load to thigh
Variations: knee brace, locking joints, hyperextension check/stop strap to reduce terminal impact sound
Joints and corset pros/cons/indications
Durable, user adjustable, ML stability, hyperextension stop, can load through thigh to partially offload limb
Heavy, bulky, noisy, pistoning
ML instability (short limb, ligament laxity), heavy duty user
Describe waist belt and fork strap suspension
Belt around waist suspends through connection via fork strap which attaches to the socket or a supracondylar cuff
Elastic webbing improves knee flexion comfort in swing
Waist belt and fork strap pros/cons/indications
User adjustable, sensory feedback, visual verification
Pistoning, potentially bulky
Early fittings, auxiliary suspension
Describe supracondylar suspension and requirements
Compresses soft tissue proximal to femoral condyles, requires min. ML-PML difference of 12mm
Supracondylar - use of foam liner vs removable medial brim/wedge
12mm+ ML-PML -> foam liner
25mm+ ML-PML -> removable brim/wedge
Supracondylar pros/cons/indications/contraindications
Self suspending, low profile w/o additional suspension components, better ML stability vs PTB
High trim lines (sitting)
ML instability (short limb, ligament laxity)
Excessive soft tissue or firm muscle in PML, high activity contraindicated
Describe supracondylar cuff (strap) suspension
Leather cuff wraps around distal thigh above femoral condyles and suspends over the patella (not condyles)
Provides tension from full extension to ~60° knee flexion for suspension with reduced tension for sitting
Attachment location for supracondylar cuff
1” proximal and posterior to lateral midline MPT level (can vary within a square inch)
Supracondylar cuff pros/cons/indications/contraindications
User adjustable, sensory feedback, low cost
Pistoning
PTB socket with good ML stability
ML instability contraindicated
Types of mechanical suspension
Knee sleeve
Locking liner
Describe knee sleeve suspension
Sleeve adheres to outside of socket and thigh skin or exposed gel, suspension via friction
Elastic (more conforming but more pistoning), neoprene, gel
Knee sleeve pros/cons/contraindications
Conceals socket trim lines
Heat, bulk around knee
Poor hand dexterity contraindicated
Describe locking liner suspension
Gel liner with notched pin, lanyard, magnet, etc. adheres to skin and engages with mechanical lock in distal end of socket
Locking liner pros/cons/contraindications
Audible click confirms suspension, quick and easy donning, accommodates volume changes
Relative pistoning, maintenance (cleaning, wear/tear or liner and lock components)
Hygiene concerns contraindicated
Types of atmospheric suspension
Passive suction
Active vacuum
Describe passive suction suspension
Cushion gel liner used with a knee sleeve that seals on socket and skin or exposed gel; can use socks
Or
Seal-in gel liner with embedded rings that compress against socket wall for seal, doesn’t require knee sleeve
One way valve, distraction force reduces pressure/increases suction force inside socket
Difference between pressure in passive vs active suction
Passive suction = atmospheric pressure (reduces with distraction)
Active vacuum = negative pressure system with air actively extracted
Passive suction pros/cons/contraindications
Relatively reduced pistoning, potentially reduced in-socket rotation
Chance of material failure, bulk and heat with sleeve
For seal in liner, expected volume changes are contraindicated
Describe active vacuum suspension
Requires gel liner with sleeve or seal-in liner. Sleeve seals against exposed gel and not skin
Air actively extracted via mechanical or electronic pump
Active vacuum pros/cons/contraindications
Minimized pistoning, rotation, and daily volume fluctuations
Counterintuitive for prosthetists, maintenance
Lack of cognition/acceptance and gross volume fluctuations contraindicated
Osseointegration advantages and disadvantages
Eliminates need for socket, easy donning
High infection rate, other complications, sx risks, healing time
Describe interfaces (in general)
Contacts skin, material between skin and socket
Types of interfaces
Fitting socks
Gel liners
Foam liner (Pelite, Keasy cone)
Sock thickness is referred to as
Ply
Goal sock ply fit for sock-only interface
5 ply
Types of gel liners and features
Locking liner (distal umbrella), cushion liner, seal-in liner
Fabric matrix stabilizes and increases durability, reduces longitudinal stretch/pistoning, allows circumferential stretch
Urethane liners may have no fabric matrix
Preflexed liners reduce stretch or patellar discomfort while sitting
Different thickness profiles, shapes, sizes
How to don a socket with a liner with no outer matrix
Use lotion or spray alcohol to allow liner to slide into socket
Factors for consideration in choosing an interface
Preference Limb profile/shape Skin integrity Hand dexterity Perspiration/activities Knee anatomy (prominent patella) Hygiene Contact allergies
Differentiating contact allergy vs bacterial or fungal infection
Allergy: entire area of contact irritated with distinct border
Bacterial or fungal: inconsistent coverage (refer to dermatologist)
TPE liner material properties (thermoplastic elastomer)
Poor memory
Easy to reflect for don/doff
Tends to pack out quickly, requires more thickness to absorb force
Tackiness (patella tension)
20-30 durometer
Silicone liner material properties
Memory Less thickness required to absorb force compared to TPE Easy don/doff No coatings or fabric covers to wear out Durable Doesn’t protect bony anatomy as well Doesn’t stretch out as quickly Solidifies tissue (good for fleshy limbs)
30-50 durometer
Urethane liner material properties
Memory Less thickness required to absorb force vs TPE Least thinning with compression Protects bony limbs Less moisture build up Doesn’t compress tissue as much Some drag when pushing into socket Good for fleshy limbs
30-50 durometer
Liner property: compressive resistance
Change in thickness under load
High stiffness - less compression, less likely to offload peak pressures
Low stiffness - compressed more, distribute peak pressures
Liner property: shear resistance
Ability to move from forces in parallel plane
High stiffness - higher stress on skin
Low stiffness - sensitive skin, less intimate fit
Liner property: stretch resistance
Ability to lengthen when pulled
High stiffness - less likely to stretch/piston
Low stiffness - more stretch/piston
Liner property: adherence
Force required to move liner along skin
High frictional coefficient - req. more force, less likely to slip, can cause shear
Low frictional coefficient - req. less force and more likely to slip
What level of partial foot amputation do you lose ankle and calf musculature during walking
Transmet and higher
Ankle disarticulation pros/cons and treatment
Good weight bearing area, anatomical suspension, longer lever arm
Poor cosmesis, limited component space/possible LLDcy
Window - medial or posterior
Stovepipe liner, expandable wall with cylindrical shape socket
Symes vs Boyd vs Pirogoff
Symes = removal of calcaneus
Boyd = horizontal transaction of calcaneus
Pirogoff = vertical transaction of calcaneus
Effects of PFA in gait
Reduced lever arm
Premature toe break
Reduced step length
Lisfranc joint level vs Chopart level
Lisfranc = Tarsometatarsal (keep midfoot)
Chopart = Transtarsal (keep hindfoot only)
Goal of toe amputation prosthesis
Restore normal foot mechanics/foot shape
Prevent toe migration
Treat underlying pathology
Goal of ray resection prosthesis
Maintain foot position in shoe
Restore foot mechanics and shape (arches)
Amputation of which ray(s) result in loss of forefoot motion
1st and 5th ray resection loses FF motion
Goals of MTPJ amputation prosthesis
Maintain cosmetic appearance
Maintain foot position in shoe
Protect RL from shoe
Restore foot mechanics
Goals of TMA prosthesis
*limited ambulation w/o prosthesis
Protect shoe from deforming forces w/walking
Maintain foot position in shoe
Protect RL
Restore foot mechanics
Goal of lisfranc and chopart prostheses
*weight bearing with limited walking
Manage contracture
Suspend shoe
Protect RL
Restore mechanics
GRAFO + partial foot
