Implant camouflage - how apparently excellent registry data can mask poor implant results: an international multi-centre case-control study.

Abstract

The purpose of this research is to highlight a new issue facing national joint registries called 'Implant Camouflage', whereby a poorly performing implant combination within an overall brand portfolio is hidden by other high performing implant combinations. This was an international multi-centre case-control study assessing implant combinations within the NexGen® TKA portfolio. There were 9392 primary TKA components included with 1744 'high-risk' cases and 7648 'standard-risk' controls. The median time to follow-up was 7.4 (IQR 4.8-9.4) years in the cases and 10.4 (IQR 7.5-13.8) years in the control group. The primary outcome variable was revision for aseptic loosening. All-cause revision was a secondary outcome variable. Cox regression and Kaplan-Meier (KM) survival analysis was used to determine survivorship free of revision for aseptic loosening. The high-risk cases had significantly higher rates of revision for aseptic loosening (5.2 % v 0.4 %, p < 0.001) and all-cause revision (7.9 % v 2.9 %, p < 0.001). KM curves demonstrated higher rates of aseptic loosening in the high-risk cases with no intersection of 95 % confidence intervals with the controls. On univariate analysis, older age (p < 0.001) and higher BMI (p < 0.001) patients had significantly higher rates of revision for aseptic loosening. After multivariate analysis, the high-risk component cases were the most significant predictor of early failure for aseptic tibial loosening (p < 0.001). The NexGen® Option-LPS Flex and Option-LPS GSF combinations have over a 10-fold higher revision rate for aseptic loosening when compared to other implant combinations in the NexGen® portfolio.