Finite Element Analysis of Tibial Stem Extensions in Total Knee Arthroplasty: Influence of Varus–Valgus Loading and Fatigue Resistance

Tibial stem extensions are widely adopted in revision total knee arthroplasty (TKA), yet their relevance in complex primary cases is not fully established. This finite element (FE) analysis compared tibial virtual constructs with and without a stem extension to assess stress distribution, deformation, and fatigue endurance. The model included the femoral component, tibia, tibial tray component, polyethylene insert, cement mantle, and optional stem, tested under compressive loading combined with varus and valgus angles of 3°, 5°, 7°, and 10°. In the standard configuration without a stem, peak stresses reached ~259 MPa under varus and ~300 MPa under valgus, while stem use consistently lowered stresses by roughly one quarter. Fatigue performance also improved, extending survival from about 360,000 cycles (equivalent to ~2 years) to more than 600,000 cycles (>3–4 years) with a stem. These results indicate that tibial stems help distribute loads more evenly, restrict micromotion, and enhance long-term durability. Clinically, such benefits may be most relevant in demanding primary TKA scenarios, including severe malalignment, bone loss, or compromised bone stock.