Comparative retrieval analysis of a novel anatomic tibial tray backside: alterations in tibial component design and surface coating can increase cement adhesions and surface roughness.

BACKGROUND: With the Persona® knee system a novel anatomic total knee design was developed, which has no pre-coating, whereas the predecessor knee system is pre-coated with polymethylmethacrylate (PMMA). Joint registry data have shown no decrease in risk of aseptic revision of PMMA pre-coated tibial components compared with non-pre-coated implants. The aim of this retrieval study was to compare the amount of cement adhesions, geometry and surface features between the two knee designs and to correlate them with the underlying reason for revision surgery. METHODS: Retrieval analysis was performed of 15 NexGen® and 8 Persona® fixed-bearing knee implants from the same manufacturer retrieved from two knee revision centres. A photogrammetric method was used to grade the amount of cement attached to the tibial tray backside. The geometry and dimensions of the tibial trays, tray projections and peripheral lips were measured using digital callipers and compared between the two different designs. To measure the surface roughness on the backside of the tibial tray, a contact profilometer was used. To investigate differences between the two designs statistical analyses (t-test) were performed. RESULTS: All Persona® trays showed evidence of cement adhesion with a % area of 75.4%; half of the NexGen® trays had cement adhesions, with a mean value of 20%. There was a significant difference in the percentage of area covered by cement between the two designs (p < 0.001). Results from the contact profilometer revealed that Persona® and NexGen® tray backsides showed a similar lateral (1.36 µm and 1.10 µm) and medial (1.39 µm and 1.12 µm) mean surface roughness with significant differentiation (p < 0.05) of the lateral and medial roughness values between the two designs. Persona® stems showed a significantly higher mean surface roughness (1.26) compared to NexGen® stems (0.89; p < 0.05). CONCLUSION: The novel anatomic knee system showed significantly more cements adhesions and a higher surface roughness which was most likely attributed to the most obvious design and coating alteration of the tibial tray. This study provides first retrieval findings of a novel TKA design recently introduced to the market.

Comparative retrieval analysis of antioxidant polyethylene: bonding of vitamin-E does not reduce in-vivo surface damage.

BACKGROUND: With the Persona® knee system a new polyethylene formulation incorporating vitamin-E which aims to reduce oxidation and maintain wear resistance was introduced. Although in-vitro studies have demonstrated positive effects of the vitamin-E antioxidants on UHMWPE, no retrieval study has looked at polyethylene damage of this system yet. It was the aim to investigate the in-vivo performance of this new design, by comparing it with its predecessor in retrieval analysis. METHODS: 15 NexGen® and 8 Persona® fixed-bearing implants from the same manufacturer (Zimmer Biomet) were retrieved from two knee revision centres. For retrieval analysis, a macroscopic analysis of polyethylene using a peer-reviewed damage grading method was used (Hood-score). The roughness of all articulating metal components was measured using a contact profilometer. The reason(s) for TKA revision were recorded. Statistical analyses (t-test) were performed to investigate differences between the two designs. RESULTS: The mean Hood score for Persona® inserts was 109.3 and for NexGen® 115.1 without significant differences between the two designs. Results from the profilometer revealed that Persona® and NexGen® femoral implants showed an identical mean surface roughness of 0.14 µm. The Persona® tibial tray showed a significantly smoother surface (0.06 µm) compared to the NexGen® (0.2 µm; p < 0.001). Both Hood score and surface roughness were influenced by the reasons for revision (p < 0.01). CONCLUSIONS: The bonding of the antioxidant vitamin-E to the PE chain used in the novel Persona® knee system does not reduce in-vivo surface damage compared to highly crosslinked PE without supplemented vitamin-E used in its predecessor knee system NexGen®. However, the Persona® titanium alloy tibial tray showed a significantly smoother surface in comparison to the NexGen® titanium alloy tibial tray. This study provides first retrieval findings of a novel TKA design and may help to understand how the new Persona® anatomic knee system performs in vivo.