Instability following TKR:

- Discussion:
    - may result from unequal flexion and extension gaps; (instability in extension or flexion due to MCL or LCL incompetence);
    - posterior subluxation:
            - excessive posterior tibial slope:
            - loose posterior stabilized TKR;
                  - references:
                        - Flexion instability without dislocation after posterior stabilized total knees.
            - from previous patellectomy
            - loose PCL (PCL retaining TKR);
                  - references:            
                        - Flexion instability after primary posterior cruciate retaining total knee arthroplasty.
                        - Early, incapacitating instability of posterior cruciate ligament-retaining total knee arthroplasty.
    - varus subluxation in extension or flexion due to unequal gaps;
    - in the report by TK Fehring et al, the authors evaluated the causes of revision surgery;
            - between 1986 and 1999, 440 patients with TKR were referred for revision surgery;
            - of the 440 patients who had revision surgery, 279 (63%) had revision surgery within 5 years of their index arthroplasty:
            - 105 of the 279 patients with early failures (38%) had revision surgery because of infection;
            - 74 (27%) had revision surgery because of instability;

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- Isolated Polyethylene Exchange:
    - references:
          - Polyethylene exchange only for prosthetic knee instability.
          - Clinical Results of Modular Polyethylene Insert Exchange with Retention of Total Knee Arthroplasty Components.
          - The Effectiveness of Isolated Tibial Insert Exchange in Revision Total Knee Arthroplasty.
          - Isolated liner exchange: not always a useful option in revision TKA. Counterpoint.
          - Isolated tibial insert/liner change: it can work. Point.

   

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- references:

- Early Failures in Total Knee Arthroplasty. Thomas K. Fehring MD. CORR 2001;2001:315-318

- Knee instability after total knee arthroplasty.

- Insall Award paper. Why are total knee arthroplasties failing today?

- Flexion and extension gap balancing in revision total knee arthroplasty.

- Flexion instability in primary total knee replacement.