Aseptic loosening, induced by particles or stress-shielding, remains the major cause of long-time revision of endprosthesis. Hybrid material compounds represents a promising approach to combine advantageous material properties of oxide-ceramics and titanium-alloys. Within the scope of this computational study, biomechanical capability of simplified constructs of cementless knee endoprosthesis were investigated under intraoperative and postoperative loading conditions.
The constructs consisted of either monolithic alumina-toughened-zirconia (ATZ) or a material compound of ATZ and Ti-6Al-4V or Ti-42Nb alloy. Finite element analysis was performed to analyse the maximum stress at cementless fixation, the pull-off strength at high flexion, and the strain energy density under loading conditions of a two-leg stance.
Normal stresses in the ATZ during cementless fixation decreased from 1641.0 MPa in the monolithic construct to 161.6 MPa in the ATZ - Ti-6Al-4V compound and 236.8 MPa in the ATZ - Ti-42Nb compound. Accordingly, the hybrid material construct seems suitable for cementless fixation, whereas the monolithic one experiences high stresses above the ultimate flexural strength (755 – 1163 MPa). Pull-off force of the hybrid implant construct (ATZ – Ti-6Al-4V: 2855.1 N, ATZ – Ti-42Nb: 1826.0 N) decreased compared to the monolithic design (3576.6 N) because of decreased stiffness of the construct and accordingly lower contact area. Therefore, studies on the primary implant stability should be addressed in future studies. Strain energy density increased by 13.3% (ATZ - Ti-42Nb compound vs. monolithic ATZ) in the distal resection area, highlighting the potential of hybrid material compounds to reduce stress-shielding.
The concept of the hybrid knee prosthesis showed promising results in this computational study. However, future studies have to address the biomechanical capability and primary stability of the ceramic-titanium material compound using standard implant designs and experimental study setups.