  In total knee arthroplasty (TKA) force is transmitted into the tibia by a
combined plate-stem device along with cemented or cementless stem fixation. The
present work analyzes this force transmission in finite element simulations
with the main aim to avoid reported postsurgical bone density reduction as a
consequence of a reduced tibial bone loading. In the numerical analysis
different implant materials, stem/extension lengths and implant-to-stem
interface conditions are considered, from a stiff fully cemented fixation to
sliding contact conditions with a low friction coefficient. The impact of these
variations on bone loading changes are measured by (i) decomposing the total
force into parts mediated by the plate and by the stem and by (ii) post-surgery
strain energy density (SED) deviations. Based on a bionics-inspired perspective
on how nature in pre-operative conditions carries out force transfer from the
knee joint into the tibia, a modified implant-bone interface is suggested that
alters force transmission towards physiological conditions while preserving the
geometries of the standard plate-stem endoprosthesis design. The key aspect is
that the axial force is predominantly transmitted through the plate into
proximal bone which requires a compliant bone-stem interface as realized by
sliding friction conditions at a low friction coefficient. These interface
conditions avoid stress shielding almost completely, preserve pre-surgery bone
loading such that bone resorption is not likely to occur.
