Types of Instability


1.  AP Instability

2.  Varus Valgus Instability

3.  Global Instability

4. Frank Dislocation


TKR Dislocation APTKR Dislocation Lateral


AP instability


A.  Loose in flexion



- can get knee dislocation / post jump



- excessive posterior femoral resection

- PCL failure


A.  Excessive posterior femoral resection


Revise femur

- posterior femoral augments + stem


B.  Failure of PCL in CR knee


Revision femur and poly

- insert PS femur and poly

- need to have CCK revision equipment available


B.  Loose in extension


Excessive distal femoral resection

- revise femoral component

- distal femoral augments + stem


B.  Loose in flexion and extension


Insufficient poly thickness / wear

- insert larger poly


Varus-Valgus instability




A. Iatrogenic collateral ligament injury



- advance / imbricate / augment / reconstruct collateral

- full revision to VVC / CCK constrained implant


B.  Failure to balance knee 



- under release deformity in the concavity



- increase poly thickness, further releases in concavity


TKR Varus Coronal Instability TKR Varus Instability Increase Poly Thickness


C.  Insufficient poly / loosening over time



- equal varus and valgus instability



- increase poly thickness


TKR Instability Varus and Valgus 1TKR Instability Varus and Valgus 2


TKR Instability Increase Poly Thickness


3.  Global instability


Unstable in  sagittal and coronal planes


1.  Insufficient poly thickness / poly wear



- increase poly thickness


TKR Poly WearTKR Poly Wear Lateral


2.  Loosening / collateral ligament damage



- revise to highly constrained prosthesis


TKR Global Instability APTKR Global Instability Lateral