General Prosthetics Flashcards
Knee Disarticulation Amputation Types (5)
True KDA
Gritti-Stokes
Callender
Burgess
Mazet
Typical gait Pattern of Forefoot and Hindfoot Amputees (4)
Characterized by less active plantarflexion
Delayed progression of the centre of pressure
Starter stride length tendency to prematurely shift body weight to the contralateral side
Gait is wide based, slower and less energy efficient
Bench Alignment for HDA Prosthesis
Sagittal
Alignment reference line passes
-through the COR of the socket in 5 degrees anterior tilt
-posterior to the hip joint (1cm?)
-anterior to the knee joint (1cm?)
-through the weightbearing surface of the foot
Transverse
- All joint axes run parallel to each other and are perpendicular or slightly externally rotated from the LOP
- socket in LOP
Frontal
Alignment reference line passes
-through a point on the socket midway between ASIS and IT on amputated side
-through the center of the hip, knee, and heel
-pelvis, hip, knee, ankle all the parallel to the ground
HDA Biomechanics at Terminal Stance/Pre Swing
- socket tilts anteriorly (forces prox/post and distal/ant)
- force increased on hip ext stop, knee destabilizes and flexes
- GRF - post to hip, post to knee, ant to ankle
Chopart Amputation
- tarsals transected, calcaneus and talus remain
- tendency to hold a varus and equines position
- leg length discrepancy as a fit issue
- ankle movement between residuum and socket -> pressure and shear
- alignment and shoe fit
- able to distal end bear/self suspend
HDA Socket Design Principles (3)
1) Seat for vertical loading of the ischium
- along with encapsulation of the illiac crests helps control rotation
- weight bearing surface which can tolerate force
2) Lateral support of sound side illium both A and D
- keep socket snug in A/P and M/L
- allows control of the prosthesis by pelvic tilt
3) Suspension over the crest of the illium on the amputated side
KDA: External Hinges vs. Polycentric/4 bar linkage
External Hinges
- no swing phase controls
- cosmetic advantage/disadvantage
- length KC vs. Width
Polycentric
- stable
- cosmetic disadvantage
Specific Assessment requirements for Symes (5)
- size of heel pad
- degree of heel pad mobility
- tolerance to distal end pressure
- malleolar remnants
- previous distal end weight bearing
Symes Casting Techniques (4)
- circumferential wrap/longitudinal split
- obturator door
- slab
- Berkeley casting stand
HDA Biomechanics at Midstance
GRF is
-anterior to ankle COR (external dorsiflexion moment)
-anterior to knee COR (external knee extension moment)
-posterior to hip COR
(external hip extension moment)
Each joint should be locked, supporting weight without collapse (contralateral swing)
HDA Biomechanics at Initial Contact and Loading Response
GRF is -posterior to ankle COR (external plantarflexion moment) -anterior to knee COR (external knee extension moment) -through or posterior to hip COR (external hip extension moment)
Potential Socket Designs for KDA or Symes (5)
- obturator
- segmented liner (stove pipe)
- molded leather
- silicon (expandable walls)
- bivalve socket
Advantages/Disadvantages of a Symes Amputation
Advantages
- distal end weight bearing
- self suspension
- long lever arm
- increased proprioception and prosthetic control
- increased area for distribution of forces
Disadvantages
- cosmesis
- risk of heel pad hypermobility and displacment
- donning/doffing issues
- limited room for components
Lisfranc Amputation
- tarsal metatarsal level
- may see equinovarus deformity
- LLD
- decreased ROM
- short lever arm -> typically above ankle design
- suspension an issue
Problems present after amputation involving metatarsals (3)
- reduced plantar weight bearing surface
- impaired pronation/supination during gait
- loss of active push-off
Elevated Vacuum Suspension (benefits) (6)
- gold standard
- little to no pistoning
- reduced daily volume fluctuations
- improved healing and skin health
- improved proprioception/user feedback
- better venous return
Static Alignment of a Transtibial
- meet and greet, explain your intention
- skin check
- donning procedure
- sit to stand
- socket fit assessment
- suspension
- length
- gross alignment, instructions
Measurements for TT Casting
-Circumferences at PTB and intervals distal
-diameters at PTB A/P, KC M/L, oblique medial flair, just post to fibular head
-lengths- PTB->distal end
PTB ->ground
-other - foot length and heel height
-cosmetic measurements
-any needed for suspension method
Where to Place Knee Joints on BK Socket
- axis should be perpendicular to LOP, therefore parallel with posterior wall
- 2.25’’ proximal to PTB/posterior brim
- mid-point between PTB/posterior brim (or 60% posterior including patella)
- error on proximal and posterior to lift stump out of socket in flexion/sitting
Foot Overview (4)
SACH
- solid ankle cushion heel
- high durability, low cost
- compliant with exoskeletal
SA
- allows controlled plantarflexion/dorsiflexion
- heavier, more expensive
- stabilizes knee of TF user
MA
- movement in all planes
- ground compliance
- wear, up keep and repairs needed
Dynamic
- ESR often carbon fiber
- less ground compliant
- typically durable
Bench Alignment of a Transtibial
Frontal:
Alignment reference line passes
-through center of socket with appropriate varus/valgus
-through center of heel
Sagittal:
Alignment reference line passes
-through center of rotation fo socket with 5 degree plus contraction of preflexion
-through center of weight bearing surface of the foot
Transverse:
Socekt is in the line of progression 5-7degree toe out
Liner Materials (3)
Silicone
- most durable
- easy to clean
- good with shuttle lock
Urethane
- best pressure distribution (flows)
- porous (stains and stinky!)
- excellent at reducing shear
Thermoplastic elastener
- user and prosthetist friendly
- good protection against socket forces
- stinky
Pin Locks (3)
Clutch
- infinite locking positions
- ability to “wind in”
- no available feedback
- maintenance and wear
- not ideal for dirty/wet environments
Rachet
- audible
- movement between serrations, noise, wear
Smooth(friction)
- plain pin = reduced wear
- no audible click
- infinite locking positions
- sensitive to moisture and debris
Goals of Dynamic Alignment (3)
- Mimic normal gait pattern
- Maximize comfort and function
- Optimize energy consumption and stabililty
Indications for a Thigh Corset (4)
- Knee instability M/L
- weak quads or knee hyperextension A/P
- inability to tolerate weight bearing forces distally
- patient request
Why Pre-flex a TT Socket (2)
- extension reserve
- angle of inclination
PTB Socket Design
- specific weight bearing
- load tolerant areas and unload intolerant
- ideal for new amputees due to less dependence on limb volumes for fit
Why total contact? (4)
- venous return
- minimize pressure (F/A)
- increase feedback
- prevent negative pressure
TT amputation Surgery (3)
- posterior flap (Burgess), long posterior tissue with good vascular supply, M/L suture line
- fish mouth - A/P suture line
- Ertle - fibular bone bridge
Why to use liner (5)
- low amount of soft tissue coverage
- intolerant skin
- redundant tissue
- suspension needs
- odd limb shape
Common Liner Problems (5)
- perspiration
- skin issues, blisters/rashes
- irritation over boney prominences
- distal end problems, blisters, milking, discolouration
- hygiene related, bacteria, fungal infections etc.
6 Determinants of Gait
6 optimizations to minimize excursion of C of G in vertical AND horizontal planes, REDUCE ENERGY CONSUMPTION OF AMBULATION
1) Pelvic rotation
2) Pelvic tilt
3) Knee flexion in stance phase
4) Ankle mechanism
5) Foot mechanism
6) Lateral displacement of the body
5 Prerequisites of Gait
- Stability in stance
- Swing phase clearance
- Prepositioning of foot for initial contact
- Adequate step length
- Energy conservation
Total contact vs Total Surface Bearing (TSB)
Total contact is not equal contact due to multiple densities and sensitivities
Contact everywhere (total contact) - improves venous return, minimize pressure, increase feedback
Maximize area (A), P=F/A
Traditional PTB socket is specific weight bearing, but total contact
Total surface bearing aims for even pressure everywhere on the residuum, uses LINER interface
