Updated: 1/4/2020

TKA Sagittal Plane Balancing

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Introduction
  • Goal is to obtain a gap that is equal in flexion and extension. This will ensure that the tibial insert is stable throughout the arc of motion.  
    • balancing is complex due to two radii of curvatures (patellofemoral articulation and tibiofemoral articulation)
    • often requires soft tissue release and bony resection to obtain balance
  • General Rules    
    • adjust femur if asymmetric 
      • distal femur cut affects extension gap
      • posterior femur cut affects flexion gap
    • adjust tibia if problem is symmetric (same in both flexion and extension)
      • tibia cut affects both flexion and extension gap
    • remember increasing/decreasing the size of the femoral component only changes the AP diameter and therefore affects the flexion gap only.  
 Evaluation & Treatment
  •  The following chart shows different conditions found with the trials in place and the treatment strategy for each condition.
  Tight in Flexion
(can not fully flex)  
Balanced in
Flexion
 
Loose in Flexion
(large drawer test) 
Tight in Extension (can not fully extend)
 
Tight in Extension, Tight in Flexion

Problem:
Did not cut enough tibia
Solution:
Cut more proximal tibia 
Tight in Extension, Balanced in Flexion
 Problem:
Did not cut enough distal femur or did not release enough posterior capsule 
Solution:
1) Release posterior capsule 
2) Cut more distal femur
  
Tight in Extension, Loose in Flexion

 Problem:
Distal femur too long.
Solution:
1) Resect more distal femur or use thinner distal femoral augmentation wedge (revision scenario)
2) Upsize femoral component 
Balanced  in Extension
 
Balanced in Extension, Tight in Flexion
 
Problem: 
Did not cut enough posterior femur, PCL scarred and too tight.
Solution: 
1) Decrease femoral component size which required an increase in resection of the posterior femoral condyle Recess vs. release of PCL Release posterior capsule Decrease femoral component size which required an increase in resection of the posterior femoral condyle
2) Recess vs. release of PCL
3) Release posterior capsule
Solution: 
1) Decrease femoral component size which required an increase in resection of the posterior femoral condyle
2) Recess vs release of PCL
3) Release posterior capsule
4) Recut proximal tibia with increased slope

Balanced in extension, Balanced in Flexion (Perfect)
Balanced in Extension, Loose in Flexion
  
 Problem: 
Cut too much posterior femur.
Solution:
1) Increase size of femoral component (AP only)
2) Posteriorize femoral component (augment posterior femur). 
Loose in Extension
 (recurvatum)
 
Loose in Extension, Tight in Flexion

 Solution:
1) Downsize femur and use thicker tibial insert until balanced. 

Loose in Extension, Balanced in Flexion
 Problem:
 Cut too much distal femur.
Solution:
 1) Augment distal femur 
Loose in Extension, Loose in Flexion
 Problem:
Cut too much tibia.
Solution:
1) Use thicker tibia PE
2) Add medial & lateral metal augments to tibial tray


 

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