Abstract
Abstract
Introduction
At our national explant retrieval unit, we identified an unusual pattern of backside-deformation on polyethylene (PE) inserts of contemporary total-knee-replacements (TKRs). The PE backside's margins were inferiorly deformed in TKRs with central-locking trays. We reported that this backside-deformation appeared to be linked to tray debonding. Moreover, recent studies have shown high-rate of tray debonding in PS NexGen TKRs. Therefore, we hypothesised that backside deformation on PS inserts may be more than on CR inserts.
Methodology
We used peer-reviewed techniques to analyse changes in the bearing (wear rate) and backside surfaces (deformation) of PE inserts using coordinate measuring machines [N=61 NexGen (CR-39 and PS-22) TKRs with non-augmented-trays]. Multiple regression was used to determine which variable had the greatest influence on backside-deformation. The amount of cement cover on trays was quantified as a %of the total surface using Image-J software.
Results
There was no statistically significant difference (p=0.238) in median (IQR) wear rate of the CR PEs 18 (12–28) mm3/year and PS PEs 14 (8–20) mm3/year. The PE backside-deformation median (IQR) of PS [297(242–333) µm] was significantly higher (p=0.011), when compared with CR [241(161–259) µm]. Multiple regression modelling showed that duration in-vivo (p=0.037), central-clearance between insert and tray (p<0.001) and constraint (p=0.003) were significantly associated with PE backside-deformation. 27(69%) of CR and 20(91%) PS exhibited ≤10% of cement cover on tray.
Conclusion
This explant study showed backside-deformation on PS inserts was more than on CR inserts. Therefore, indicating a high-rate of tibial tray debonding in PS compared to CR NexGen TKRs.
