Topology-optimised auxetic tibial implants: A finite element study toward reducing aseptic loosening

The American Joint Replacement Registry 2025 reported that 29.2% of the primary total knee arthroplasties were revised due to aseptic loosening of the implant. The press fit technique posed a considerable risk of periprosthetic fractures and end-of-stem pain in the bone. Although lattice porous structures enhance osseointegration, high porosity may affect the fatigue behaviour of the implant. Auxetic material (structure) has a negative Poisson's ratio. It expands laterally under tension and densifies under compression, offering improved load transfer and reduced micromotion. Finite element analysis (FEA) was performed to topologically optimise a Knee (Tibial) implant and incorporate an auxetic structure to the implant to minimise strain shielding and prevent implant loosening. With the introduction of an auxetic lattice structure, the implant-bone micromotion decreased from 0.085 mm (solid implant) to 0.0039 mm (topology optimisation with 97% mass retention), indicating a reduced risk of implant loosening with the auxetic implant.