Modern Total Knee Arthroplasty Design Can Replicate Similar Joint “Awareness” to Unicompartmental Knee Arthroplasty

Introduction: The Forgotten Joint Score (FJS) is a scoring system that measures how natural the prosthesis feels following joint arthroplasty. When comparing functional outcomes of patients with unicompartmental knee arthroplasty (UKA) versus total knee arthroplasty (TKA), studies often report the UKA as the preferred knee. The purpose of this study is to determine how natural modern TKA designs feel in comparison to UKA, as well as traditional TKA, post-surgery.

Methods: 200 UKA and 400 TKA patients were retrospectively reviewed from two institutions from 2014-2017. UKA procedures were performed using a single implant, 200 TKAs were performed using a standard PS design (traditional TKA) and 200 TKAs performed using a TKA designed to recreate more normal kinematics (modern TKA). FJS questionnaires were obtained at one year following surgery.

Results: Mean follow-up of 13.6 months (range, 12-23 months). The highest FJS were reported by the patients that underwent modern TKA, followed by the UKA patients, and lastly, the traditional TKA patients (77.3 ± 19.3; 73.7 ± 24.7; 72.0 ± 19.8, p=0.049). A significant difference in FJS was observed between modern TKA and traditional TKA (p=0.049). Biometric factors associated with a higher FJS were male sex (B 4.68, p=0.009, lower BMI (B -0.575, p=0.005). When corrected for sex and BMI, the use of modern TKA was associated with higher FJS compared to UKA (B 6.69, p=0.004), no significant difference was found between traditional TKA and UKA.

Conclusion: Based on our analysis, there is no significant difference in joint awareness between FJS of patients who undergo UKA and TKA with a modern design. However, a difference in joint awareness was found between modern TKA and traditional TKA designs. Modern TKAs of have the potential to achieve the natural feeling of artificial joint forgetfulness that is associated with UKA, although longer follow-up is necessary.