Correlation of cross-linking as measured by the trans-vinylene index and in vitro wear of polyethylene from various acetabular liner brands

Listen to Simon and Amy discuss the paper 'Correlation of cross-linking as measured by the trans-vinylene index and in vitro wear of polyethylene from various acetabular liner brands' published in the November 2024 issue of Bone & Joint Research.

Click here to read the paper.

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Transcript

[00:00:00] Welcome to another episode of AI Talks with Bone & Joint from the publishers of Bone & Joint Research. Today we're discussing the paper 'Correlation of cross-linking as measured by the trans-vinylene index and in vitro wear of polyethylene from various acetabular liner brands', published in November 2024 by P. Waal, R. Heuberger, A. Pascucci, T. M. Winkelreid, M. Fersner, N. Ikken, M. Schlappe, R. Purzel and E. Gauthier. 

I'm Simon, joined by my co-host, Amy. 

Hello Simon. This paper delves into how the trans-vinylene index, or TVI, correlates with the wear rates in different polyethylene acetabular liners used in total hip arthroplasty.

Their aim was to examine if the TVI, which measures the degree of cross-linking achieved through irradiation, could predict wear rates in polyethylene liners. This is crucial for enhancing the longevity of total hip replacements.

For their methods, the researchers collected 47 polyethylene acetabular liners from ten different brands over a [00:01:00] year. These samples were either retrieved from revisions or were unused components. They utilized Fourier-transform infrared spectrometry to measure the TVI and the oxidation index and used a pin-on-disk test to measure wear.

 Fourier-transform infrared spectrometry specifically allows for precise measurement of the TVI and oxidation index by analysing the spectral features of the materials. The pin-on-disk tests simulate wear, to understand how these materials might perform in a real-world biomedical context. 

Simon, what were the key findings? 

The TVI is known to be a reliable measure of the absorbed irradiation dose in polyethylene. They found that it remained stable over time in vivo, and, as expected considering specifications, there was a clustering of the results by brand. Higher TVI values corresponded to lower wear rates, indicating that more cross-linking typically improves wear resistance. However, there were some unexpected results, particularly with Medacta's Highcross liners and Zimmer Biomet's [00:02:00] Durasul liners.

What were those unexpected results? 

For the Highcross liners, the TVI indicated much lower absorbed irradiation doses than anticipated, suggesting variability in manufacturing. This could explain the higher wear rates observed in this brand. Conversely, Durasul liners had significantly higher TVI values than expected, possibly due to their electron beam irradiation technique, which seems to create a higher degree of cross-linking.

Fascinating. They also noted that electron beam irradiation might lead to better cross-linking compared to gamma irradiation at equivalent doses, though it requires more controlled conditions to ensure consistency. 

Indeed. They supported this with Monte Carlo simulations of polyethylene irradiation, showing significant differences in depth dose curves for electron versus gamma irradiation. This profoundly affects how radiation doses are absorbed within the material, influencing the cross-linking and wear characteristics. 

One practical takeaway [00:03:00] is that the TVI can predict wear performance, which is essential for designing better polyethylene liners. However, it also raises concerns about manufacturing consistency, particularly for brands like Medacta's Highcross.

Absolutely. This suggests that clinical outcomes could be improved by selecting polyethylene components based not only on their classification as highly cross-linked, but also by understanding their specific irradiation and manufacturing processes. To wrap up, Amy, what would you say are the key insights from this study?

Firstly, the TVI is a reliable measure of the irradiation dose in ultra-high molecular weight polyethylene and correlates well with wear rates. Secondly, there's significant variability in the actual cross-link density achieved by different manufacturing techniques. Finally, better control over irradiation processes, like in the case of electron beam irradiation, can potentially improve the wear resistance of polyethylene liners used in hip arthroplasty.

Thanks Amy. This study underscores the importance of precision in [00:04:00] the manufacturing process to ensure the longevity of hip replacements. Looking forward to our next episode, where we delve into another intriguing topic. 

Indeed, Simon. Thank you all for tuning in to this episode of AI Talks with Bone & Joint. Stay tuned for more news from the world of biomedical research.