When Polyethylene Exchange Is Appropriate for Prosthetic Knee Instability

Introduction: Prosthetic knee instability is a common cause of patient dissatisfaction and early failure after total knee arthroplasty (TKA). Strategies to manage such instability are dependent on the recognition of the presenting instability pattern because some require full revision, whereas others can be managed by polyethylene exchange (PE) only. This retrospective chart review classifies and reports on a series of patients where PE only was used to manage an unstable TKA. Methods: Of 1606 revision TKA patients, 4% underwent an isolated PE for prosthetic knee instability. All cases were classified using the novel OrthoCarolina Prosthetic Knee Instability Classification System. This classification system was established to guide surgeons in the diagnosis and surgical management of periprosthetic knee instability. The final data set included 41 patients at an average follow-up of 43 months. Results: Of the patients treated with poly exchange only for an appropriate indication (ie, coronal instability with competent ligaments or global instability), 63% felt their knee was stable, whereas 37% felt they remained unstable after revision. Additionally, only 59% had improvement in their pain, whereas 41% were dissatisfied with their pain relief after revision. Discussion: Despite the use of this technique when indicated, the results of PE only with regard to pain and instability are unpredictable. Only approximately 50% of patients became stable and had adequate pain relief. Patients and surgeons alike should understand that this low morbidity option does not guarantee a good result regardless of whether it is used for an appropriate indication. Obtaining stability and pain relief in a patient with prosthetic knee instability remains a significant challenge. Therefore, the key to avoiding prosthetic knee instability is through prevention at the time of primary surgery. Prosthetic knee instability remains difficult to manage despite intuitive and appropriate indications for PE only.