Transtibial Prosthesis Flashcards
4 Key Components to Transtibial Prosthesis
Prothetic Foot
Shank
Socket
Suspension
Transtibial Shank - EXOskeleton
- prior to vietnam war
- lamniate that formed outside dimensions
- stong enough to support body weight
- heave and inflexible
- very little adaptability
- very durable
Transtibial Shank - ENDOskeleton
- internally supported by an internal pylon/pipe
- interchangability
- post fabrication adjustable
- strength - very durable
- light weight
- covering options
Transtibial Shank - Pylons
- narrow vertical support connecting the socket to the ankle/foot assembly (shank)
- shock and torque absorption pylons can be added for additional responsiveness, stress, shear and torque reduction
Socket Design: PTB WB force Distribution
- developed 1950s
- most commonly prescribed
- WB areas
- through PT and post popliteal tisues
- fibular shaft
- tibial shaft
- tibial flares
- fem condyles
- Protect:
- fibular head
- peroneal nerve
- anterior distal tibia
- HS tendons
- tibial crest,
- ant tibial tubercle
- distal fibula
- patella
- adductor tub
PTB Socket Advantages and Disadvantages
- Exert forces in all directions equally
- advantages
- evenly distrib. forces across RL - max WB
- liner offeres good shear and friction reduction
- enhancement comfort
- Disadvantages
- skin irritations
- some hypersensitive areas cannot tolerate the even pressure
Socket Interface b/t Residual Limb and Socket Design
Hard Socket = Thin Sock
Soft Socket = Foam “pelite” liner
Hard Socket Interfaces
- Rigid plastic interface
- direct contact b/t socket and residual limb
- shearing/friction are minimized
- enhanced cosmesis
- easy to cleen
- durable = easy to replace thin sock
- requires increased skill of prosthesis
- difficult to adjust/modify
- may not be appropriate for fragile skin
- MATURE LIMBS ONLY
- minimize bulk
- reportedly cooler
- 3 goals
- help cushion - good fit
- accomodate volume change
- wick moisture
Soft Liner Interface
Foam Pelite Liner
Advantage:
- adds cushion
- easily modifiable
- suspension can be incorporated
Disadvantage:
- adds bulk
- increases friction
- insulative properties
- skill required for donning/doffing
Soft Interface
Custom Liners
- indicated for uniquely shaped and/or scarred limbs
- were the first silicone liners available
- advantages
- reduced friction and shear
- suspension mechanisms may be included
- disadvantages
- expensive and hot at first
- potential for skin problems - humidity and friction
- add bulk
Soft Interface
Off the Shelf Liners
- most manufacturers now have their own line
- advantages:
- reduce friction and shear
- suspension may be included
- different thickness and styles
- silicone, mineral oil gels, even with aloe
- customizable
- disadvantage
- may be hot
- add bulk
- potential for skin problems
Suspension - Cuff Strap
advantages:
- simple and effective means of suspension
- suspends over the condyles
- attachment points approximate knee center
- leather or leather and elastic
disadvantages
- does not provide AP or ML stability
- may impede circulation and knee flexion >90
- not very cosmetic
Suspension
Waist Belt and Fork Strap Suspension
Advantages
- removes all suspension burden from the limb
- elastic anterior strap - accomodate extra length in knee flexion during end stage of stance and assists with knee extension during swing
- usually added as an auxillary suspension
- often used for high lvel athletes
Disadvantages
- hot
- allows for piston action
- bulky
Suspension - PTB Supracondylar
Advantages:
- often dont need another suspension
- added ML stability
- some recurvatum control
- increased socket surface lowers pressure overall
- one piece design
Disadvantages:
- higher trim lines
- requires dexeterity to don/doff
Suspension
Locking Pin
-pin is incorporated into the distal end of the gel liner and must be guided into the shuttle at the distal end of the socket
Advantage:
- pistoning reduced
- secure suspension
Disadvantage:
- suspension forces concentrated distally
- mechanical complications
- flexion limitations
- some feel milking action at and of residual limb
Suspension
Suction(most common now)
-consists of one way valve into the socket that allows air to escape in conjunction with a gel suspension sleeve that seals the top of the socket preventing air from coming in
Advantage:
- best suspension available
- improved cosmesis
- suspension not concentrated on the RL
Disadvantage:
- durability
- knee flexion limitations
- heat
- skin irritations
Suspension
Sleeve
Advantage:
- improved cosmesis
- suspension is not concentrated on the RL
- OFTEN USED AS AN AUXILLARY SUSPENSION
Disadvantage:
- durability
- knee flexion limitations
- heat
- skin irritations
Biomechanics of PTB
- maximize weight bearing capacity of RL (use flexion in interface (5-8 deg)
- alignment - maintain ML stability at midstance on prosthetic side (initial contact inset 1/4 in)
- encourage knee flexion throughout stance on prosthetic side (initial foot placement 1 1/2 in post to midpoint of socket at med tib plataue)
Normal Expectations
- patient should be comfortable walking
- base of support 2-4 in between heel centers
- knee flexion approximately 10-15 deg after initial contact
- foot moves smoothly into loading response
- socket should not gap at lateral brim, no increased pressure at medial brim
Terminology
Heel Lever Arm
Distance from end of prosthetic heel to midpoint of shoe
-Provides support from intital contact to midstance to allow smooth descent of the prosthetic foot and controlled knee flexion
Terminology
Toe Lever Arm
Distance from midpoint of shoe to toe
- provides support from midstance to terminal stance
- allows patient to roll over the foot in a smooth manner
Terminology
Lever Arms
Altering the position of the foot DF or PF or positioning the foot anterior or posterior to the socket alters the toe and heel lever arms
