Gait implications for Prosthetics and orthotics Flashcards
ankle-knee interaction: stance
- static stance: ankle position indirectly controls knee position
- DF ankle: GRF vector posterior to knee axis-flexion moment at knee
- with PF ankle: GRF vector anterior to knee axis- extension moment at knee strengthen HS
GRF AFO
- ankle can dorsiflex: GRF vector posterior to knee axis creates flexor moment
- ankle held in neutral: GRF vector anterior to knee axis - creates extensor moment
Biomechanical Objectives of transtibial prostheses
- Maximize WB
- improve medial/lateral stability
- encourage knee flexion
Biomechanical Objectives of transtibial prostheses
Maximize WB
- distribute forces to pressure tolerant areas (patellar tendon, medial tibial flare)
- to pressure-sensitive areas (tibial crest)
- set socket in flexion
Biomechanical Objectives of transtibial prostheses
improve medial/lateral stability
- inset prosthetic foot (medial to knee) to mimic slight knee varus at midstance
- more lateral to knee = knee valgus
Biomechanical Objectives of transtibial prostheses
encourage knee flexion
- move prosthetic socket anterior in relation to foot
- use firm heel bumper
- SACH: solid ankle cushioned heel to give some DF/PF motion
Biomechanical Objectives of transfemoral prostheses
- full, comfortable WB on residual limb
- medial/lateral stability of hip/pelvis during stance
- A/P knee stability during stance
- Permit normal step length with non amputated limb
- control of prosthetic knee during swing
Biomechanical Objectives of transfemoral prostheses
full comfort weight bearing on residual limb
- total contact force distribution
Biomechanical Objectives of transfemoral prostheses
Medial/lateral stability of hip and pelvis during stance
design features
Design features:
- inset prosthetic foot
- lateral wall of socket adducted
- narrow medial/lateral dimension of socket to stabilize femur
Biomechanical Objectives of transfemoral prostheses
Anterior/posterior stability during stance
knee joint set posterior to GRF vector
Biomechanical Objectives of transfemoral prostheses
permit normal step length with non-amputated limb
- socket set in slight flexion
- decreases amount of hip extension needed in non-amputated limb to take full step on prosthetic side
Biomechanical Objectives of transfemoral prostheses
control of prosthetic knee during swing
- want knee to flex in early swing, then extend fully in preparation for heel strike during late swing
- depends on gait speed, type of knee
excess knee flexion: initial contact into loading response (step off)
- foot goes to foot flat quickly into excess knee flexion during early stance
- transtibial prosthesis: socket in too much flexion, heel bumper too frim
- ankle-foot orthosis: solid ankle to heel rocker for bottom shoe
excess knee extension midstance to terminal stance
- transtibial prosthesis: socket not flexed enough, heel bumper too soft => delays tibial advancement
- ankle-foot orthosis: ankle permits plantarflexion => knee can hyperextend
transtibial prosthetic sock issues
too many ply
residual limb not seated down into socket
findings:
- too long on prosthetic side (iliac crest heights)
- redness below patellar tendon
- may see pistoning