Revision TKA for Instability: Poorer Outcomes after a Previous Aseptic Revision.

Instability is a common indication for early revision total knee arthroplasty (rTKA). The comparative performance of instability rTKA performed after primary TKA and instability rerevision TKA (rrTKA) performed after a previous rTKA performed for any aseptic indication have not been defined. This study was performed to determine the rate of adverse outcomes for patients undergoing aseptic instability TKA revision following a primary TKA or a previous aseptic any-cause rTKA. After obtaining Institutional Review Board approval, we retrospectively identified 126 rTKA and 28 rrTKA component revision procedures performed for an exclusive instability diagnosis between January 1, 2011 and April 30, 2018. We excluded patients undergoing isolated liner exchange, single component revision for mid-flexion instability, and patients treated with a constrained hinge. Patient demographic characteristics, medical comorbidities, time to initial revision TKA, and adverse postrevision outcomes (reoperation, component revision, infection, amputation) were assessed using paired Student's -test or Fisher's exact test with a -value < 0.05 used to determine significance. Patients in the rrTKA cohort were more commonly female (57.1 vs. 27.8%,  < 0.01), with no other demographic differences. The rrTKA cohort had higher reoperation (39.3 vs. 18.4%,  = 0.02) and component revision rates (25.0 vs. 8.7%,  = 0.03), with a trend towards early reoperation < 2 years after surgery (25.0 vs. 11.1%,  = 0.07). The rrTKA cohort also had higher adverse outcomes related to infection (14.3 vs. 1.6%,  = 0.01), extensor mechanism failure (14.3 vs. 3.2%,  = 0.04) and above-knee amputation (14.3 vs. 2.4%,  = 0.02). Component revision is beneficial for patients with TKA instability; however, higher adverse outcome rates occur after instability rrTKA performed after a previous aseptic any-cause rTKA. Infection prevention and extensor mechanism protection are important to minimize the most common adverse outcomes identified among patients undergoing aseptic rrTKA for instability.