General criteria for ankle joint replacements

Question 1

List 4 potential reasons why ankle replacements are not as advanced as other joints

Answer 1

Ankle not frequently involved in primary OA

In secondary OA and RA ankle is usually affeted with other joints such as subtalar so replacing ankle alone is not adequate

Ankle functions with subtalar so motion of this joint has to be taken into account also

Arthrodesis is successful if subtalar joint remains healthy

Question 2

What is arthrodesis?

Answer 2

Fusion of the joint in a position of function

Question 3

What are the advantages of ankle arthrodesis?

Answer 3

Relieves pain in stiff joint without need to compensate for resulting loss of movement

Question 4

What are the disadvantages of ankle arthrodesis?

Answer 4

Abnormal loadings on the knee and subtalar joint on the same leg
shortening of stride which has consequences for opposite limb joints (pateint will walk out toed so the subtalar joint acts as dorsiflexor of the foot)

Question 5

What materials make up current ankle joint replacements?

Answer 5

Metal (CoCr or SS) and HDP

Question 6

List 3 reasons why ankle replacement designs have not been lasting long enough?

Answer 6

Loads across the joint larger than anticipated

Fixation is difficult due to small bony areas for support

Restriction in the movement of the subtalar joint (such as stiffness caused by assoc. arthritis) - subjects ankle to large axially generated torques

Question 7

What are the difficulties in fixation of ankle replacement?

Answer 7

Tibial bone beneath the joint surface is mainly soft cancellous bone (rapidly widens then narrows)

On talar side area for fixation is very small