Prosthetics - Ankle Flashcards
What are the 3 objectives of prosthetics replacement?
comfort
function
cosmesis
What 5 component groups of a prosthesis are there?
interface alignment functional cosmetic structural
What 3 forces are transmitted through interface components?
support
stabilisation
suspension
What are support forces?
axial or proximally directed forces associated with the beating of body weight
What are stabilisation forces?
perpendicular forces associated with the resistance to or modification of moments acting around joints
What are suspension forces?
anatomical or suction forces associated with maintaining prosthesis attachment
How are sockets designed?
determined by level of amputation
avoid loading pressure-sensitive areas
apply forces to pressure tolerant areas
What is a Syme’s amputation?
amputation where the foot is amputated but the heel pad is left so it can weight bear
What is a transfemoral amputation
Above knee amputation
Give an example of an interface component
a socket
What are some examples of suspension devices?
cuffs and straps - pelvic belt, supracondylar cuff, elasticated sleeve
socket liners - ICEROSS silicone socket liner with shuttle lock
What are the two general requirements for a functional component?
must be able to weight bear
allow controlled movement
What are the requirements of ankle-foot devices?
absorb shock just after heel strike
allow a smooth transition to foot flat and mid stance
resist dorsiflexion and if possible store energy from mid stance to heel off
provide push off through energy return during late stance
Why does the ankle begin to plantar flex after heel strike?
the GRF is behind the ankle joint axis
Describe the action of the pretibial muscles during heel strike
contract eccentrically to absorb energy
the prosthetic ankle-foot device must stimulate this energy absorption
Describe the ‘foot flat’ stage
ankle is in around 10 degrees of plantarflexion.
the plantar flexion moment decreases as the GRF moves anteriorly and pretibial muscle activity drops
as the GRF becomes anterior the GRF moment becomes one of dorsiflexion
the prothetic ankle foot device must allow smooth controlled transition to foot flat
Describe the mid-stance stage
ankle continues to dorsiflex
plantarflexors contract eccentrically to control the rate (soleus, gastrocnemius, tibias posterior)
prosthetic device must simulate smooth controlled dorsiflexion
Describe the heel off phase
ankle dorsiflexes to about 15 degrees - calf muscles contract strongly to counteract dorsiflexion and provide active push off to propel the subject forward
Describe the toe off phase
the normal ankle has reaches around 20 degrees of plantarflexion
the prosthetic device returns to the plantigrade position under the action of the energy storing leaf spring or compressed dorsiflexion bumpers
Describe the swing phase
the normal ankle dorsiflexes slightly to improve toe-clearance at mid-swing
prosthetic device remains plantigrade
Name some articulated devices
the uniaxial foot
multi-axis Greissinger
multi-axis multiflex
Name some non-articulated devices
SACH foot
energy storing foot
flex-foot & Springlite (pistorius)
pathfinder
Describe the relative costs of the SACH foot, pathfinder and Flexfoot.
SACH - £60
Pathfinder - £1800
Flexfoot - £800-3000+
