Instability

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

 

Issue

- can get knee dislocation / post jump

 

Cause

- 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

 

Causes

 

A. Iatrogenic collateral ligament injury

 

Options

- advance / imbricate / augment / reconstruct collateral

- full revision to VVC / CCK constrained implant

 

B.  Failure to balance knee 

 

Cause

- under release deformity in the concavity

 

Management

- increase poly thickness, further releases in concavity

 

TKR Varus Coronal Instability TKR Varus Instability Increase Poly Thickness

 

C.  Insufficient poly / loosening over time

 

Diagnose

- equal varus and valgus instability

 

Management

- 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

 

Options

- increase poly thickness

 

TKR Poly WearTKR Poly Wear Lateral

 

2.  Loosening / collateral ligament damage

 

Options

- revise to highly constrained prosthesis

 

TKR Global Instability APTKR Global Instability Lateral