Primary Total Knee Arthroplasty Revised for Instability: A Detailed Registry Analysis.

Abstract Background Instability after total knee arthroplasty (TKA) is a common but poorly understood complication. Methods Data from a large national registry was used to study patient and prosthesis characteristics of 2,605 TKA revisions for instability. The cumulative percent revision (CPR) was calculated using Kaplan Meier estimates, and Cox proportional models used to compare revision rates. The rate of further revision was analysed with regard to prostheses used in the first revision. Results Instability increased from 6% of all first revision procedures in 2003 to 13% in 2019. The revision risk was lower for minimally stabilized prostheses, males, and patients ≥65 years. Polyethylene insert exchange was used for 55% of revision procedures, using a thicker insert in 93% and a change in insert conformity in 24% of CR knees. The increase in either thickness or conformity had no effect on rate of further revision. After a revision for instability, 24% had a second revision by 14 years. Recurrent instability accounted for 32% of further revisions. A lower second revision rate was seen after revision of both femoral and tibial components, and where constrained components were used. Conclusion Revision for instability is increasing. Revising both femoral and tibial components led to a lower rate of second revision compared to a change of insert alone. Recurrent instability was common.