Prosthesis design features

Question 1

Which prosthesis are todays total knee prostheses said to be derived from?

Answer 1

Burnstein Total Condylar Prosthesis

Question 2

What are the 4 parts of a total condylar prosthesis?

Answer 2

Anterior flange
HDP tibial tray
Femoral component (CoCr)
Tibial component (CoCr)

Question 3

How does the femoral component of a knee replacement differ from that of a normal knee?

Answer 3

Replacement = symmetrical 
Normal = medial condyle larger than lateral

Question 4

Why do normal knees have a larger medial than lateral condyle?

Answer 4

To aid the axial rotation achieved during the last phases of full extension

Question 5

What is the disadvantage of completely copying the asymmetry off the normal knee?

Answer 5

Doubles the sixe of the required inventory (cost)

Question 6

In practice what determines the the degree of constraint of a knee prosthesis?

Answer 6

The surface shape design of the tibial component

Question 7

What is the advantage of posterior stabilised designs?

Answer 7

Prevent posterior femoral subluxation of the femur over the tibia
Cause the femur to ‘roll back’ as it flexes

Question 8

How are knee prostheses anchored?

Answer 8

PMMA cement

Peg or other projection `

Question 9

What alternaties to cemented knee porstheses have been tried?

Answer 9

Porous coated beads and meshes (generally resistricted to the PCL-retaining type)