Instability after total knee arthroplasty.

Instability after total knee arthroplasty is reported to result in implant failure, and substantial instability often requires revision surgery. Successful outcomes can be achieved after revision total knee arthroplasty, particularly if the etiology of the instability is identified before the revision procedure. After careful clinical and radiologic analysis, instability can be classified as extension instability, flexion instability, or genu recurvatum. It is important to understand the causes and recommended treatments of each type of instability.