Impact of anatomical adaptation in cemented femoral stems on mechanical properties and alignment

Polished tapered femoral stems are widely used in total hip arthroplasty (THA) for their excellent long-term outcomes. However, anatomical mismatches in Asian populations increase the risk of periprosthetic femoral fractures and malalignment. This study evaluated the mechanical properties and radiographic alignment of the VLIAN stem-a cemented, polished, double-tapered stem with a rounded shoulder design developed for Asian femoral anatomy-compared to the Exeter stem. Mechanical testing assessed rotational resistance and stiffness using cobalt-chromium stems cemented into custom jigs and composite femur models. Rotational torque and load-displacement curves were analyzed. For clinical evaluation, 654 Japanese patients undergoing primary cemented THA were retrospectively reviewed: 275 received the Exeter stem (2013-2018) and 379 the VLIAN stem (2018-2023). Radiographs were analyzed for stem alignment, Dorr classification, and femoral neck-shaft angle. Results showed no significant difference in rotational resistance or construct stiffness between designs. Radiographic analysis demonstrated significantly smaller varus angles with the VLIAN stem, particularly in Dorr type C femurs and those with lower neck-shaft angles. These findings suggest that anatomical design modifications, such as a rounded shoulder, improve alignment without compromising mechanical strength. Further studies are needed to evaluate long-term clinical outcomes.