Treatment of Flexion Instability After Primary Total Knee Arthroplasty: Operative and Nonoperative Management of 218 Cases

Background: For patients with flexion instability, there is a paucity of literature on the effectiveness of nonoperative management, and series on revision TKAs are limited. The purpose of this study is to evaluate effectiveness and prognostic factors of nonoperative management of flexion instability, and report survivorship, clinical outcomes, and radiographic results after revision TKA for flexion instability. Methods: We identified 218 patients with flexion instability after primary TKA through our total joint registry between 1990 and 2019. Mean age was 66 years, 59% were women, and 58% had a cruciate-retaining (CR) implant. Initially, 152 patients (70%) were treated nonoperatively. First-time revision TKA was ultimately performed in 173 patients. Kaplan-Meier survivorship was calculated. Knee Society Scores and radiographs were reviewed. Mean follow-up was 6 years. Results: Of the 152 patients treated nonoperatively, 66% reported no improvement. Patients with a CR design (hazard ratio [HR] 3.3, P < .001), inflammatory arthritis (HR 1.6, P = .03), smokers (HR 2.1, P = .04), and patient-reported instability (HR 3.8, P < .001) or effusions (HR 3.5, P < .001) were more likely to undergo revision. Of the 173 revised, the 10-year survivorship free of any re-revision was 87% with recurrent flexion instability (7), global instability (3), and infection (3) being most common. Knee Society Scores improved from 50 to 65 (P = .14). At final follow-up, all implants were well-fixed. Conclusion: In this large series of flexion instability after primary TKA, nonoperative management led to improvement in one third. Patients with a CR design or with patient-reported instability and/or effusions were most likely to undergo revision. Revision TKA demonstrated modest 10-year functional improvements and good survivorship. Level of Evidence: IV (retrospective), Therapeutic.