Femoral stress distribution in fully hydroxyapatite-coated cementless versus polished cemented stems with identical geometry: a thermoelastic stress analysis.

INTRODUCTION: Stress shielding and altered load transfer remain major concerns in total hip arthroplasty (THA). Stem fixation method and material properties strongly influence femoral stress distribution, but data directly comparing cementless and cemented stems of identical geometry are limited. MATERIALS AND METHODS: Six fourth-generation composite femurs were used. Three were implanted with a fully hydroxyapatite-coated cementless stem, and three with a polished cemented stem. Mechanical loading of 100-1900 N at 5 Hz was applied to simulate single-leg stance. Thermoelastic stress analysis (TSA) was used to evaluate surface stress distribution across Gruen zones. Linear mixed models assessed differences between groups. RESULTS: Before implantation, the highest stress was observed in the proximal femur. After implantation, stress shifted distally in both fixation methods. The cementless stem maintained higher compressive stress in the proximal-medial region compared with the cemented stem, which demonstrated a more uniform stress distribution between the medial and lateral cortices. TSA measurements confirmed significant proximal stress reduction with cemented fixation, while cementless fixation preserved proximal loading more effectively. CONCLUSION: This simulation study showed that fixation method and material influence short-term femoral stress distribution, even when stem geometry is identical. These findings describe only mechanical behavior under simplified conditions. The use of composite femurs, the one-size difference between stems, and the short-term evaluation limit the generalizability of the results. Further research using cadaveric models and clinical follow-up is required to clarify long-term remodeling and support stem selection in total hip arthroplasty.