A Comparison of Isolated Tibial Insert Exchanges for Global Instability to Full Revisions for Flexion Instability in Revision Total Knee Arthroplasty

Abstract

Background: Instability remains a leading cause of revision total knee arthroplasty (TKA). However, whether a full component revision (FCR) or an isolated tibial insert exchange (ITIE) is indicated remains complicated with conflicting evidence. This study compared the outcomes of patients undergoing ITIE vs FCR for instability. Methods: A retrospective review was performed on 172 consecutive revision TKAs for global or isolated flexion instability. Diagnosis of symmetric global instability vs isolated flexion instability was based on pre-revision examination in the clinic and confirmed by rigorous numerical flexion and extension gap measurements intraoperatively. Patient-reported outcome measures and associated clinically relevant thresholds were evaluated using a significance level of 0.05. Results: There were 144 patients who underwent FCR for flexion instability, while 28 underwent ITIE for global instability. While not statistically significant, a greater percentage of FCR patients met the minimal clinically important difference threshold for the Knee Injury and Osteoarthritis Outcome Score for Joint Replacement (69 vs 38%; P = .11); while there was no difference in minimal clinically important difference between FCR and ITIE in other patient-reported outcome measures (P ≥ .28). Patients were "very satisfied or satisfied" in 58% of the ITIE group vs 56% of the FCR group (P = .51). Conclusions: Study results demonstrate that ITIE can be successful after revision TKA given the specific indication of symmetric global instability with well-fixed and well-positioned components. However, FCR is preferred in the case of flexion instability and the surgeon must be vigilant in their specific instability etiology within each patient.