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

www.nature.com/scientificreports OPEN Exploratory in vitro study of inductive heating–assisted refixation in cemented hip stems Magnus Reulbach1,3, Patrick Evers2,3, Henning Windhagen1, Florian Nürnberger2 & Eike Jakubowitz1 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 FPO = 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. Keywords Total hip arthroplasty, Revision surgery, Hip implant loosening, Refixation, Inductive heating, Acoustic emission analysis Aseptic loosening poses a significant risk to the long-term success of total hip arthroplasty (THA)1. According to the German Arthroplasty Registry (EPRD), in 2023, aseptic loosening was reported as the leading cause of THA revisions, with the stem being revised in 63 % of revision cases2. Aseptic loosening represents a partial or complete loss of the stem fixation in the absence of an infection, due to insufficient stability or particle-induced osteolysis3. In cemented THA, this loss of fixation commonly occurs at the stem-cement interface4. The long-term stability of cemented THA depends on the adequate immobilization of the stem in the bone cavity by the PMMA-based bone cement5. Clinically, two different stem designs are used to achieve immobilization. These differ fundamentally in their mechanical fixation principles: the “force-closed” and the “composite beam” designs6. With the force-closed principle, a polished surface facilitates controlled subsidence of the stem after debonding, which, in combination with its tapered shape, enables mechanical stabilization through force closure driven by a combination of radial forces and surface friction at the macroscopic level. This design provides excellent long-term stability but is associated with a higher risk of revision due to postoperative periprosthetic fractures7,8. In contrast, the stem of a composite beam design is secured within the bone cement mantle through mechanical retention at a microscopic level due to its matte surface finish. Ideally, this interlocking prevents relative motions in the stem-cement interface. However, complete immobilization is not achievable, leading to an increased risk of revision due to the growth of relative movements in the cement mantle over time9. Due to this gradual stem debonding, the roughened surface — actually intended to enhance the fixation — acts like a rasp, accelerating cement mantle wear9,10. This process ultimately results in mechanical retention loss and wear particle-induced osteolysis, necessitating revision surgery9,11–13. 1Department of Orthopedic Surgery, Laboratory for Biomechanics and Biomaterials (LBB), Hannover Medical School, Anna-von-Borries-Strasse 1-7, 30625 Hannover, Germany. 2Institut für Werkstoffkunde (Materials Science), Leibniz University Hannover, An der Universität 2, 30823 Garbsen, Germany. 3Magnus Reulbach and Patrick Evers have equally contributed email: Scientific Reports | (2026) 16:16278 | https://doi.org/10.1038/s41598-026-50093-1 1 During a stem revision, the main procedures are removal of both the stem and the cement mantle, along with debridement of the affected soft and hard tissues, before inserting a new stem14. Extracting the cement is a complex and time-consuming procedure with the risk of severe complications, including bone perforations and fractures15,16. To mitigate these complications, the cement-in-cement revision technique was introduced as an alternative16. This technique involves preserving the original bone-faced cement mantle part, into which the new stem is inserted along with new cement17–19. The success of this technique depends mainly on the cement mantle quality as contaminations from media like blood, bone marrow, and saline can compromise the new cementcement interface bond11,19. Due to such contaminations, cement-in-cement revisions are reported to result in decreased interface shear strengths of up to 85 %17,20. The problem of the ever-present, progressive loosening of cemented stems should generally be solved to improve long-term stability and thus significantly increase patient safety. In the case of the composite beam design with its matte surface, one solution could be to restore the mechanical retention to its original state. Since this retention is mechanical and the PMMA-based bone cement is a thermoplastic polymer that does not develop adhesive bonding to the metallic stem10, refixation could be achieved by briefly heating and softening the cement at the interface. Inductive subcutaneous surface heating of the metallic stem could prevent the need for the extraction of the stem from the bone cement mantle. Simultaneous axial loading of the stem would generate radial forces in the interface again, so that a new microstructural retention can be generated. In previous in vitro experiments, the effects of physiological conditions on the mechanical and thermal properties of bone cement were investigated21,22. Bone cement undergoes a fluid uptake, leading to a higher thermal contact conductance with the metallic stem and a reduction in its glass transition temperature and Vicat softening temperature between 10 °C and 16 °C resulting in values around 90 °C. Nevertheless, Vicat softening measurements showed that even in the non-aged, dry state, thermoplastic PMMA bone cement already exhibits pronounced softening between 90 °C and 95 °C. This suggests that sufficient softening for refixation can be achieved without evaporating the water present at the cement–implant interface. The aim of this exploratory in vitro study is to analyze in a simplified model whether a loosened (...truncated)