Lower Limb Biomechanics and Prosthetics Flashcards
mean amputee age and main cause
69 years
80% PAD
what are the objectives of prothetic replacement
comfort
- socket fit, force transmission
function - stability, controlled movement
cosmesis
- static (colour, shape, texture)
- dynamic (gait pattern)
force transmission - what are the 3 types of force
support
- axial forces associated with BW bearing
stabilisation
- forces perpendicular to the axis of the limb and associated w/ moments acting around the joint
suspension
what are the components of the prosthetic that should be considered
interface components alignment components functional components cosmetic components structural components
what determines socket design
Level of the amputation
avoid loading pressure-sensitive areas
apply force to pressure-tolerant areas
what is Syme’s amputation
amputation through the ankle joint
disarticulation
what is transfemoral amputation also known as
above knee amputation
what are examples of suspension devices
cuffs and straps
- pelvic belt (transfemoral)
- supracondylar cuff (transtibial)
socket liners
what is the general functional requirements for prothesis
must be able to bear weight
and allow controlled movement
what are requirements for ankle-foot devices
absorb shock just after HS
allow smooth transition to foot-flat
resist dorsiflexion
provide push-off
what happens during HS in anatomical foot and what does the prosthetic ankle-foot need to replicate
first plantigrades then the ankle begins to plantarflex due to GRF acting behind ankle long axis
in normal gait, the pre-tibial muscles contract eccentrically to absorb energy
prosthetic must simulate this energy absorption
what happens during foot-flat in anatomical foot and what does the prosthetic ankle-foot need to replicate
ankle is around 10degrees plantarflexed - the plantarflexion moment reduces as the point of GRF moves anterior
Pretibial muscle activity falls
as GRF continues anterior of the ankle joint, the external moment becomes one of dorsiflexion
Prosthetic ankle-foot must allow a smooth, controlled transition to foot flat
what happens during mid stance in anatomical foot and what does the prosthetic ankle-foot need to replicate
ankle continues to dorsiflex-plantarflexors (soleus and gastrocnemius) control rate
prosthetic must simulate smooth, controlled, dorsiflexion
what happens during heel off in anatomical foot and what does the prosthetic ankle-foot need to replicate
ankle dorsiflexes to 15 degrees and calf muscles contract to counteract increasing dorsiflexion moment and provide active push-off
prosthetic allows controlled dorsiflexion to around 10 degrees. Some devices store energy which is then used to provide some active push off
what happens during toe off in anatomical foot and what does the prosthetic ankle-foot need to replicate
normal ankle has reached 20 degrees plantarflexion
prosthetic returns to the plantigrade position under the action of the energy-storing leaf-spring or compressed dorsiflexion “bumpers”
what happens during the swing phase in anatomical foot and what does the prosthetic ankle-foot need to replicate
normal ankle dorsiflexes slightly to improve toe-clearance at mid-swing
prosthetic remains plantigrade
what are the 2 categories of ankle-foot devices
articulated
- uniaxial
- multiaxial
non-articulated
- solid ankle
- flexible ankle
examples of the multi-axial prosthetic
Greissinger
Multiflex
examples of the flexible ankle prosthetic
Flexfoot
what is a SACH foot
non-articulated prosthetic
w/ solid ankle, cushion heel and stiff keel
what are the principle requirements of the knee joints
stability in stance phase to support amputee’s weight
flexion in swing to allow clearance
what provides stance stability in knee prosthesis
locks
- manual or semi-automatic
brakes
- friction
- hydraulic
polycentric knee
- 4-bar linkage
free knee
- stability achieved by combo of A-P knee axis position and residual muscle action
how does friction work as a break
when weight is applied to the prosthesis, contact surfaces are pushed together and friction locks the knee
during swing phase, the springs keeps the surfaces apart, following flexion
how does polycentric 4-bar linkage work
instantaneous centre of rotation of knee joint moves as angle of flexion changes
w/ knee straight the knee centre is high in the thigh and posterior to GRF, enhancing stability
what is the requirements for swing phase control in knee prosthesis
allow knee to flex for toe clearance
control the heel rise immediately after toe-off
allow forward acceleration of the shank to ensure full knee extension at next heel-strike
control the knee extension so that terminal impact is minimised
what are swing phase control types
friction control
hydraulic or pneumatic controls
adv and disadv of friction as swing phase control
adv:
light in weight
reliable
can be adjusted by patient to suit walking speed
disadv:
cadence-specific (only works effectively at one walking speed)
adv and disadv of hydraulic or pneumatic for swing phase control
Adv:
effective over range of cadences
can be controlled by microprocessor
Disadv:
heavy
requires more maintenance
how do microprocessor controlled prothesis work
as patient walks faster, change in cadence is detected by electronics and motor closes value to stiffen the system
range of cadence over which the device is effective is increased
what is the commonest alignment system used in knee prothesis
Pyramid system
- four adjustable grub-screws in an outer collar which bear on an inverted pyramid and allow angular adjustments of up to 15 degrees in any direction
example of mis-alignment - prosthetic foot set too near the midline
causes the socket to try to rotate anticlockwise on residual limb, results in medial pressure proximally and lateral distally
remedy - shift foot laterally to bring line of action of GRF through mid-line of socket
what is the outer covering of the prosthetic “skin” normally made from
fabric, PVC or silicone “skin”
