Treatment of the unstable total knee arthroplasty.

Instability is one of the leading causes of clinical failure after total knee arthroplasty. Instability can be categorized according to three basic patterns: AP or flexion space instability, varus/valgus or extension space instability, and global instability. Surgical options for treating instability include polyethylene exchange of a modular component, revision to a more constrained component, or revision to a hinged component. The results achieved with these surgical options vary for each type of instability. In general, the use of more constrained components to manage unstable knees is favored.