What Is the Long-term Survivorship of Cruciate-retaining TKA in the Finnish Registry?
Authors: Montonen Emmi , Laaksonen Inari , Matilainen Markus , Eskelinen Antti , Haapakoski Jaason , Puhto Ari-Pekka , Leskinen Jarkko , Kettunen Jukka , Manninen Mikko , Mäkelä Keijo T. 
Published: June 2018

Abstract

Background
Survival of cruciate-retaining (CR) TKA is generally good, but there may be important differences in survivorship among devices, and different designs may not all be equally patellar-friendly. Large registry databases are needed to identify small but important differences between devices.

Questions/purposes
The purposes of this study were (1) to assess the long-term survivorship of the most common CR TKA devices with revision for any reason as the endpoint and compare the revision risk of these devices after controlling for the potentially confounding variables of age, sex, hospital volume, and primary diagnosis; and (2) to analyze these same devices with revision for secondary resurfacing of the patella as a separate endpoint.

Methods
Data were collected from the Finnish Arthroplasty Register. Over 95% of all primary TKAs are captured in the Finnish Register. We assessed Kaplan-Meier (KM) survivorship for each of the four most frequently used CR TKA designs used between years 2005 and 2015: Triathlon CR (n = 34,337), Nexgen CR Flex (n = 15,723), PFC Sigma CR (n = 15,541), and Vanguard CR (n = 9461), with revision for any reason as the endpoint. Revision was defined as a reoperation in which at least one of the components was exchanged (including insert exchange). Revisions in which the patella was not resurfaced at the primary operation and was resurfaced in the revision were studied as a separate endpoint. The mean followup times were 4.0 (range, 0-11.0) years for Triathlon CR, 3.8 (range, 0-11.0) years for Nexgen CR Flex, 5.1 (range, 0-11.0 ) years for PFC Sigma CR, and 4.9 (range, 0-10.9) years for Vanguard CR (p < 0.001). The group demographics were clinically comparable. We compared the risk of revision of these devices in the Cox multiple regression model with adjustment for hospital volume, age, sex, and primary diagnosis. There were some differences in the incidence of patellar resurfacing at the time of index arthroplasty (Nexgen CR flex 18.7%, PFC Sigma CR 18.4%, Triathlon CR 11.3%, Vanguard CR 14.4%), which was controlled by the Cox model. Implant survival analyses for Triathlon CR, Nexgen CR Flex, and PFC Sigma CR were also performed at the hospital level for the 25 largest TKA providers in Finland.

Results
The overall 10-year KM survivorships were 96% (95% confidence interval [CI], 95-96) for Nexgen CR Flex, 96% (95% CI, 96-97) for PFC Sigma CR, 94% (95% CI, 93-95) for Triathlon CR, and 94% (95% CI, 93-95) for Vanguard CR. After controlling for potential confounding variables like age, sex, hospital volume, and primary diagnosis, both Triathlon CR (hazard ratio [HR], 1.4; 95% CI, 1.2-1.6; p < 0.01) and Vanguard CR (HR, 1.4; 95% CI, 1.2-1.6; p < 0.01) had an increased risk for revision compared with the Nexgen CR Flex (the reference device). When revision with patellar resurfacing served as the endpoint, after controlling for those same confounding variables, Triathlon CR had a higher risk for revision than Nexgen CR Flex (HR, 1.8; 95% CI, 1.4-2.2; p < 0.01).

Conclusions
Despite slight differences among the studied devices, the overall 10-year survivorship of the current devices studied was good. However, there were differences in implant survival between the study devices, especially when revision for late patellar resurfacing was analyzed. Further studies adjusted for additional hospital and surgeon variables will be needed to examine and confirm our results.

Level of Evidence
Level III, therapeutic study.