Prosthetics - Ankle

Question 1

What are the 3 objectives of prosthetics replacement?

Answer 1

comfort
function
cosmesis

Question 2

What 5 component groups of a prosthesis are there?

Answer 2

interface 
alignment 
functional 
cosmetic 
structural

Question 3

What 3 forces are transmitted through interface components?

Answer 3

support
stabilisation
suspension

Question 4

What are support forces?

Answer 4

axial or proximally directed forces associated with the beating of body weight

Question 5

What are stabilisation forces?

Answer 5

perpendicular forces associated with the resistance to or modification of moments acting around joints

Question 6

What are suspension forces?

Answer 6

anatomical or suction forces associated with maintaining prosthesis attachment

Question 7

How are sockets designed?

Answer 7

determined by level of amputation
avoid loading pressure-sensitive areas
apply forces to pressure tolerant areas

Question 8

What is a Syme’s amputation?

Answer 8

amputation where the foot is amputated but the heel pad is left so it can weight bear

Question 9

What is a transfemoral amputation

Answer 9

Above knee amputation

Question 10

Give an example of an interface component

Answer 10

a socket

Question 11

What are some examples of suspension devices?

Answer 11

cuffs and straps - pelvic belt, supracondylar cuff, elasticated sleeve

socket liners - ICEROSS silicone socket liner with shuttle lock

Question 12

What are the two general requirements for a functional component?

Answer 12

must be able to weight bear

allow controlled movement

Question 13

What are the requirements of ankle-foot devices?

Answer 13

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

Question 14

Why does the ankle begin to plantar flex after heel strike?

Answer 14

the GRF is behind the ankle joint axis

Question 15

Describe the action of the pretibial muscles during heel strike

Answer 15

contract eccentrically to absorb energy

the prosthetic ankle-foot device must stimulate this energy absorption

Question 16

Describe the ‘foot flat’ stage

Answer 16

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

Question 17

Describe the mid-stance stage

Answer 17

ankle continues to dorsiflex

plantarflexors contract eccentrically to control the rate (soleus, gastrocnemius, tibias posterior)

prosthetic device must simulate smooth controlled dorsiflexion

Question 18

Describe the heel off phase

Answer 18

ankle dorsiflexes to about 15 degrees - calf muscles contract strongly to counteract dorsiflexion and provide active push off to propel the subject forward

Question 19

Describe the toe off phase

Answer 19

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

Question 20

Describe the swing phase

Answer 20

the normal ankle dorsiflexes slightly to improve toe-clearance at mid-swing

prosthetic device remains plantigrade

Question 21

Name some articulated devices

Answer 21

the uniaxial foot
multi-axis Greissinger
multi-axis multiflex

Question 22

Name some non-articulated devices

Answer 22

SACH foot
energy storing foot
flex-foot & Springlite (pistorius)
pathfinder

Question 23

Describe the relative costs of the SACH foot, pathfinder and Flexfoot.

Answer 23

SACH - £60
Pathfinder - £1800
Flexfoot - £800-3000+