Functional and radiological outcomes of total knee arthroplasty using posterior-stabilized U2 knee system: A retrospective study in 560 cases at five years of follow-up

Purpose The purpose of this study was to assess clinical and functional outcomes as well as the prosthesis survival rates of the U2 Knee system in primary total knee arthroplasty (TKA) with a minimum follow-up of four years. Methods We retrospectively analyzed 560 consecutively primary TKA performed between 2015 and 2019 due to osteoarthritis with a mean follow-up of 5.4 +/- 1.1 years. The clinical outcomes were assessed using the knee society score (KSS) and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Radiographic outcomes were assessed using the American knee society's roentgenographic evaluation system. Prosthetic survival was calculated using the Kaplan-Meier method. Results Postoperative KSS showed significant improvement at one year (Clinical: 37.4 +/- 4.1 vs. 91.9 +/- 3.7; p < 0.01; Functional: 41.2 +/- 3.3 vs. 90.6 +/- 4.8; p = < 0.01), with these improvements maintained throughout the follow-up period. The WOMAC score improved from 60 +/- 10.1 preoperatively to 10.9 +/- 8.3 (p = 0.02) at the end of the follow-up. There were 20 (3.7%) knees with radiolucent lines around the implant (< 2 mm), and none showed evidence of loosening. There were six (1.1%) revisions-four due to prosthetic joint infections and two due to periprosthetic femur fracture. The prosthetic survival was 97.8% at the study closure. Conclusion The U2 knee system demonstrates effective and safe performance for primary TKA with significant improvements in functional scores, patient-reported outcomes, and a promising prosthesis survival rate at mid-term follow-up. We will continue with the series analysis to assess the long-term outcomes.