TKA Patellofemoral Alignment

Question 1

What common errors lead to increased Q angle in TKA?

Answer 1

1) Internal rotation of the femur
2) Medializing femoral component
3) Internal rotation of tibial component
4) Placing patellar button lateral on patella

Question 2

What intra-operative techniques can be used to avoid increasing Q angle leading to lateral instability?

Answer 2

1) Externally rotating femoral component
2) Lateralizing femoral component
3) Avoiding internal rotation of tibial tray
4) Placing patellar button medial on patella

Question 3

Define Q Angle?

Answer 3

Angle btw extensor mechanism (ASIS to center of patella) and center of patella and tibial tubercle.

Question 4

Name 3 reference axiis in TKA?

Answer 4

1) Whiteside’s line (AP)
2) Transepicondylar (most consistent)
3) Posterior condylar

Question 5

What important considerations are there using a posterior condylar reference for femoral component placement?

Answer 5

Axis is internally rotated 3 degrees from epicondylar axis; therefore need to externally rotate guide 3 degrees.
Be cautious if lateral femoral condyle is hypoplastic (can lead to internally rotating femoral component)

Question 6

Internal rotation of femoral component in TKA has what effect?

Answer 6

1) Increased Q angle

2) Medial compartment tight in flexion

Question 7

What is the correct rotation of the tibial tray?

Answer 7

Neutral rotation.

Will be centered over the medial third of tibial tubercle.

Question 8

What’s the first step if lateral subluxation of of patellar component during TKA?

Answer 8

Deflate the tourniquet and recheck.

Question 9

What are the risks of not resurfacing the patella in TKA?

Answer 9

1) Increased anterior knee pain
2) Increased risk of secondary resurfacing
3) NO increased risk of revision surgery
4) NO increased risk of patellar tendon complications

Question 10

Patellar tracking issues in TKA related to malposition of components is diagnosed best with what imaging modality?

Answer 10

CT scan