Exploratory in vitro study of inductive heating-assisted refixation in cemented hip stems

To avoid highly invasive cement extraction during revision of cemented hip stems, we investigated in vitro a concept for refixation of loosened cemented stems using induction heating. The thermoplastic polymeric bone cement is softened by heating the metallic stem above the cement's glass transition temperature, possibly allowing refixation. In an exploratory study three simplified conical Co28Cr6Mo samples were corundum blasted to simulate the surface roughness of matt cemented stems. Three fixation states were produced by cementing the stem samples within a PMMA cavity: (1) initially implanted stem after cement polymerization; (2) loosened stem retained by taper self-locking; (3) refixated stem. The latter should be achieved by inductive surface heating to 95 °C and applying an axial force of 2 kN. Fixation quality was assessed from relative motions in the stem-cement interface, acoustic emissions during quasistatic torsional loading (7 Nm and 10 Nm), and axial pull-out forces of the stem from the cement mantle. Initial fixation yielded a pull-out force of F_PO = 1.99 kN ± 0.26 kN, decreasing to 0.84 kN ± 0.38 kN after loosening. After refixation, pull-out forces reached 0.89 kN ± 0.50 kN. However, in one of the three samples, the pull-out force could be restored by refixation. Therefore, the induction-based refixation concept shows potential as a less invasive alternative to conventional revision surgery but requires further validation in more clinically relevant in vitro models.