Primary stability assessment under simulated loading conditions of two β-titanium alloy hip stems versus conventional hip stem

The success of cementless total hip arthroplasty depends on primary stem-bone interfacial micromotion and long-term osseointegration. Novel β-titanium alloys (Ti27Nb and TNTZ) offer lower stiffness and superior biocompatibility compared to conventional Ti6Al4V, thus making them promising stem materials. The present finite element based study compared solid and proximally porous hip stems across these three materials under peak gait loads of normal walking and stair climbing. A CT-derived computational femur model implanted with the Stryker Accolade stem was validated against LVDT-based micromotion measurements under quasi-static axial compression. Proximal porosity was achieved using a TPMS-based gyroid architecture. Six stem configurations - solid and porous variants of Ti6Al4V, Ti27Nb, and TNTZ - were evaluated to assess how material stiffness and porous design influence primary stability. The simulation results demonstrated that the porous TNTZ stem reduced stress shielding effects by up to 10.96% compared to the Ti6Al4V stem, according to the adopted stress shielding index formulation. The porous stems, especially the porous TNTZ stem, demonstrated improved primary stability across the clinically relevant proximal metaphyseal region, although minor localized accumulation of micromotion was observed distally. Among all the analysed configurations, the porous TNTZ stem under stair climbing exhibited the lowest mean micromotion (71.58 ± 31.42 µm) while maintaining favourable proximal stability characteristics. The study outcomes highlight the potential of porous TNTZ stems for improving implant primary stability and load transfer to the host bone, although further in vivo and in vitro validations are warranted.