General criteria for knee joint replacements

Question 1

What are nearly all commerically available knee replacements made of?

Answer 1

fEM COMPONENT = COBALT CHROME

tIBIAL COMPONENT = hdp

Question 2

What problems were seen with titanium components instead of cobalt chromium?

Answer 2

Metal wear particles taken up by synovial membrane causing blackening

Question 3

What are the minimum functional kinematic requirements of a knee replacement?

Answer 3

Full extend to 180 (so can stand without quads)
Flex to 90 (walk up stairs)
Permit slight axial rotation as knee extends (to maintain natural ligament tension)

Question 4

What must be intact for screw home mechanism of knee to operate?

Answer 4

Collateral ligaments

Posterior capsule

Question 5

Which knee replacement design is the “gold standard”?

Answer 5

Total condylar

Question 6

How can it be determined that the two bearing surfaces are cut parallel?

Answer 6

Radiograph of the femur (draw a line from centre of the fem head to the knee centre)

Question 7

Why must the posterior capsule of the knee be dissected off the abck of the femur?

Answer 7

So the replacement knee can fully extend

Question 8

How are ligaments normally balanced?

Answer 8

Lengthen tightened ligaments to match slack ones

Question 9

How does the cost of a knee replacement compare to hip?

Answer 9

Knees on average cost 5x as much as hips