Peak stresses within the cement mantle increase above the yield point of bone cement when the subsidence limit is reached in polished taper stems
Mohamad Taufiqurrakhman, Alison Jones, Abdul Halim Abdullah, Mark Higgins, Benjamin V Bloch, Andrew R J Manktelow, Hemant G Pandit, Bernard H van DurenBackground:
Cemented polished taper-slip (PTS) stems are widely used in total hip arthroplasty but are associated with an increased risk of periprosthetic femoral fracture. Stem centralizers enable surgeons to achieve an even cement mantle and allow for controlled subsidence, which is essential for maintaining fixation, as this relies on the PTS implant’s interaction with the surrounding cement mantle (known as a “force-closed” mechanism). However, if subsidence exceeds the centralizer’s limit, the implant transitions to a configuration where fixation depends on direct mechanical interlocking with the cement mantle (a “shape-closed” mechanism), potentially increasing stresses within the cement mantle. The aim of this study was to quantify the stress distribution changes within the cement mantle when further subsidence is restricted using finite element analysis (FEA).
Methods:
Three commonly used PTS designs: C-Stem AMT (Johnson & Johnson MedTech, Warsaw, IN, USA), Exeter (Stryker, Kalamazoo, MI), and CPT (Zimmer Biomet, Warsaw, IN), were 3D scanned and modelled, incorporating cement mantle and centralizer gaps per manufacturer guidelines. FEA simulated loading conditions mimicking a stumble (6,900 N) with and without a distal gap to assess von Mises stress and deformation. Variations in stem materials (Stainless steel (SS316L) and Co-Cr alloys) and friction coefficient were also evaluated.
Results:
With subsidence allowance, peak von Mises stresses were concentrated in the medial calcar (Gruen zone 7), with CPT stems showing the highest stress (~45 MPa). When subsidence was restricted, stress shifted to the distal tip (zone 4), increasing by 49–102% depending on stem design and material. Co-Cr stems exhibited higher stress and displacement at the distal tip compared to SS316L stems.
Conclusions:
Restricting subsidence in PTS stems significantly increases distal cement mantle stress, which may elevate PPF risk. Stem design, material and implant-cement interface friction influence stress distribution and subsidence behavior, potentially affecting long-term implant stability.