TKR planning

Question 1

how do you determine the femoral rotation?

Answer 1

• whiteside line - perpendicular to AP axis (centre of trochlear - centre of notch)
• 3 deg ER to posterior condylar axis
• transepicondylar axis - parallel to it

Gap balancing - greater tendency to over ER

measure resection - relies on bony landmarks so maybe unreliable

Question 2

gap or measured resection?

Answer 2

• both are used to determine the rotational alignment of components in TKR
• meta-analysis shows - gap referencing may provide better clinical and radiographic outcomes

Question 3

why is it important to get femoral external rotation correct?

Answer 3

important for:
* soft tissue balancing
* patella tracking
* stability in flexion

malrotation leads to:
* polyethylene wear
* patella subluxation/ dislocation
* anterior knee pain
* patella fracture
* >3 deg malrotation lead to abnormal loading

Question 4

anterior or posterior referencing?

Answer 4

• Anterior - no notching but variation in flexion gap
• posterior - risk of notching but between flexion gap

Question 5

why is the TKR loose in flexion?

Answer 5

• excessive tibial cut
• excessive posterior tibial slope
• excessive posterior femoral cut
• femoral component too small

Question 6

why is the TKR tight in flexion?

Answer 6

• insufficient tibial cut
• insufficient posterior cut
• constriction of the posterior capsule
• oversized femur

Question 7

why is the TKR loose in extension?

Answer 7

• too much distal femur or prox tibia cut
• collateral injury

Question 8

why is the TKR tight in extension?

Answer 8

not enough distal femur or proximal tibia cut

Question 9

Tight in extension problems:
1. Tight in ext and flexion?
2. Tight in ext only

Answer 9

1. resect more tibia
2. resect more distal femur

Question 10

Tight in flexion problems:
1. Tight in flexion only

Answer 10

1. Downsize the femoral component

Question 11

Loose in flexion and extension problems:
1. loose in both
2. loose in flexion only/ & tight in ext
3. loose in extension only/ & tight in flex

Answer 11

1. use a thicker tibial insert
2. upsize femoral component
3. Augment the distal femur

Question 12

how can you define the joint line?

Answer 12

intraoperatively based on the meniscal remnant

Question 13

why is important to restore the joint line?

Answer 13

• allows normal kinematics
• change in position effects PCL, collaterals and PFJ
• change in joint line >5mm adversely effects outcome - early failure and poor satisfaction
• gap balancing is more likely to adversely effect joint line

Question 14

Joint line problems:
1. what happens with joint line elevation?
2. what happens with lowering of the joint line?

Answer 14

1. Joint line elevation
   * patella Baja
   * PF tracking issues
   * low knee scores
2. lowering joint line
   * flexion instability
   * lack of full extension

Question 15

Patella resurfacing?

Answer 15

Resurfacing:
* evidence to support both practices
* reduced pain in tricompartmental OA
* potential cause of revision in unexplained post TKR pain
* secondary patella resurfacing for anterior knee pain have worse outcomes than primary resurfacing

Benefits following groups
* obese
* RA
* tricompartmental/ PFJ arthritis

Question 16

patello femoral instability in TKR?