With an increasing total population and ageing society, the number of artificial joint replacement rises. Among all replacements, total knee arthroplasty (TKA) is widely spread [1]. The joint, comprised of a femoral and tibial component and a polyethylene articulating surface in between, is subjected to friction and wear. Caused by the complex interplay of loading from motion, body fluids and temperature, chemical reactions and microstructural changes at the implant´s surface and subsurface could take place. An often-observed phenomenon in a wide range of sliding contacts is tribologically-induced oxidation. In the worst-case, oxide formation could lead to wear particle formation within the joint and potentially to implant failure. Hence, understanding the fundamental mechanisms of this phenomenon is of utmost importance extending the lifetime of TKA.

Two zirconium nitride covered femoral components were analysed by use of Atom Probe Tomography (APT) to investigate the chemical changes and in particular the (tribo-)oxidation at the implants’ surface. The implants’ CoCr29Mo6 base material is coated with an up to 7 µm thick multilayer (alternating layers of CrN and CrCN and a top-most ZrN layer) [2]. One implant was explanted from a 72-year-old male patient (102 kg) after ~ 2 years due to early aseptic loosening [3], the other implant was a fresh one for comparison. Earlier studies found the non-articulating area of this particular explant as oxidized ZrN, whereas the articulating surfaces were polished by bone cement particles embedded in the polyethylene gliding surface [3]. When performing in-vitro tests with these implants in a knee wear simulator, Reyna et al. [4] observed oxidation marks on the femoral components within the articulating area. The results of APT will be discussed in terms of degradation mechanism of the implants’ coating.

References

[1] Statistisches Bundesamt, Fallpauschalenbezogene Krankenhausstatistik (DRG-Statistik) Operationen und Prozeduren der vollstationären Patientinnen und Patienten in Krankenhäusern (4-Steller) - 2020, 2021.

[2] J. Reich, L. Hovy, H.L. Lindenmaier, R. Zeller, J. Schwiesau, P. Thomas, T.M. Grupp, Orthopade, 2010, 39, 495–502.

[3] A. Laura, P. Reyna, J. Lützner, B. Altermann, T.M. Grupp, International Case Reports Journal, 2023, 3, 1–16.

[4] A.L. Puente Reyna, B. Fritz, J. Schwiesau, C. Schilling, B. Summer, P. Thomas, T.M. Grupp, J Biomech., 2018, 79, 88–96.