Total knee replacement survivorship by Design Philosophy: are we ignoring medial pivot design? Analysis based on the UK National Joint Registry.

The UK National Joint Registry(NJR) has not reported total knee replacement (TKR) survivorship based on design phi- losophy alone, unlike its international counterparts. We report outcomes of implant survivorship based on design phi- losophy using data from NJR's 2020 annual report. All TKR implants with an identifiable design philosophy from NJR data were included. Cumulative revision data for cruciate-retaining(CR), posterior stabilised(PS), mobile-bearing(MB) design philosophies was derived from merged NJR data. Cumulative revision data for individual brands of implants with the medial pivot (MP) philosophy were used to calculate overall survivorship for this design philosophy. The all-cause revision was used as the endpoint and calculated to 15 years follow-up with Kaplan-Meier curves. 1,144,384 TKRs were included. CR is the most popular design philosophy (67.4%), followed by PS(23.1%), MB (6.9%) and least commonly MP (2.6%). MP and CR implants showed the best survivorship (95.7% and 95.6% respectively) at 15 years which is statistically significant at, and beyond, 10 years. Observed survivorship was lower at all time points with the PS and MB implants (94.5% for both designs at 15 years). While all design philosophies considered in this study survive well, CR and MP designs offer statistically superior survivorship at and beyond 10 years. MP design performs better than CR beyond 13 years yet, remain the least popular design philosophy used. Publishing data based on knee arthroplasty design phi- losophy would help surgeons when making decisions on implant choice.