Ankle Replacement

Question 1

What other joint does the ankle function in association with?

Answer 1

the subtalar joint

Question 2

What alternative to replacement is there for the ankle joint which is more commonly used?

Answer 2

arthrodesis

Question 3

What activities of daily living are restored by replacement but not fusion?

Answer 3

walking

rising from a chair

Question 4

What are the main materials used in ankle replacements?

Answer 4

cobalt chrome
stainless steel
HDP

Question 5

List 3 reasons why ankle prostheses may fail

Answer 5

loads across the ankle are larger than anticipated

bony areas where prostheses can be fitted are barley adequate to provide sufficient support - mainly on the talar side

Any restriction of movement of the subtler joint such as stiffness from OA/RA subjects he ankle to large axial torques which adds to loosening on the already tenuous anchorage

Question 6

What is the ankle joint?

Answer 6

the joint between the tibia and the talus

Question 7

what is another name for the ankle joint?

Answer 7

tibio-talar

talocrural

Question 8

What is the normal range of motion at the ankle?

Answer 8

25-30 degrees in both dorsiflexion and plantar flexion

Question 9

How many axes of rotation does the ankle have?

Answer 9

one

Question 10

What is the tall-calcaneal joint and what motion occurs there?

Answer 10

subtalar joint

inversion/eversion

Question 11

What happens to the stride of a patient if both the ankle and subtalar joint aren’t accounted for?

Answer 11

shortened

Question 12

What activity of daily living is particularly problematic for ankle replacement patients?

Answer 12

rising from a chair

massive upper body effort is required if the ankle cannot dorsiflex

Question 13

What is the range of motion of the ankle joint required in walking?

Answer 13

15 degrees in plantarflexion and dorsiflexion

Question 14

What are the approximate maximum vertical and fore-aft loads on the ankle joint?

Answer 14

5x body weight

0.7x bodyweight

Question 15

What two classification of replacement ankle joints are there?

Answer 15

congruent

incongruent

Question 16

What is the difference between congruent and incongruent replacements?

Answer 16

congruent have matching bearing surfaces - incongruent do not

Question 17

What 4 congruent shapes have been used in ankle replacements?

Answer 17

spherical
spheroidal
conical
cylindrical

Question 18

List some benefits of spherical designs

Answer 18

freedom of rotation

compensation for subtalar joint

Question 19

List a limitation of spherical designs

Answer 19

it ha a specific centre of rotation and therefore requires careful positioning during insertion

Question 20

What is one advantage of cylindrical over spherical bearings?

Answer 20

greater angle of plantar/dorsiflexion rotation

Question 21

Why are cylindrical bearings preferred over spherical bearings?

Answer 21

Medic-Lateral space in the joint is limited and for the same width, plantar/dorsiflexion is is greater in cylindrical prostheses.

Question 22

Describe a spheroidal joint bearing and its pros/cons

Answer 22

provides plantar/dorsiflexion and inversion-eversion motion but no axial rotation because its curvature is different in the sagittal and frontal planes

Question 23

Describe and give one disadvantage of the conical type of bearing

Answer 23

provides a single axis of plantar flexion/dorsiflexion and some media-lateral resistance

it requires a greater amount of bone resection than a cylindrical shape

Question 24

Name two disadvantages of the cylindrical shape?

Answer 24

it cannot compensate for subtalar dysfunction

creates an area of concentrated stress under asymmetrical media-lateral loading

Question 25

How many axes of rotation does a cylindrical bearing have?

Answer 25

one