Mobile- versus fixed-bearing modern total knee replacements – which is the more patella-friendly design?

Abstract

Objectives Our study aimed to examine if a mobile-bearing total knee replacement (TKR) offered an advantage over fixed-bearing designs with respect to rates of secondary resurfacing of the patella in knees in which it was initially left unresurfaced. Methods We examined the 11-year report of the New Zealand Joint Registry and identified all primary TKR designs that had been implanted in > 500 knees without primary resurfacing of the patella. We examined how many of these were mobile-bearing, fixed-bearing cruciate-retaining and fixed-bearing posterior-stabilised designs. We assessed the rates of secondary resurfacing of the patella for each group and constructed Kaplan-Meier survival curves. Results Our study showed a significantly higher rate of revision for secondary resurfacing of the patella in the fixed-bearing posterior-stabilised TKR designs compared with either fixed-bearing cruciate-retaining or mobile-bearing designs (p = 0.001 and p = 0.036, respectively). Conclusions This New Zealand Registry study shows that during the last 11 years, revision procedures to resurface an unresurfaced patella in primary TKR occurred at a higher rate in fixed-bearing posterior-stabilised designs. Article focus  To investigate total knee replacements (TKRs) undertaken for osteoarthritis  To assess whether mobile-or fixed-bearing TKRs were protective of an un-resurfaced patella in terms of secondary resurfacing of the patella in modern TKR designs Key messages  New Zealand Joint Registry Study focused on TKRs implanted in numbers > 500 knees in the 11-year report  Stratification of TKRs into mobile-bearing, fixed-bearing cruciate-retaining and fixed-bearing posterior-stabilised designs, all performed without resurfacing of the patella at primary operation  Comparison of rates of secondary resurfacing of the patella between the bearing groups Strengths and limitations  A total of 20 495 primary TKRs implanted without initial patellar resurfacing, with 96% follow-up  We assumed that all secondary resurfac-ings patellar were undertaken for pain, with a constant surgeon intervention rate  There were no details in the registry regarding circumferential patella electro-cautery and its effect on rates of revision