Osteoporotic Bone Quality Significantly Increases Proximal Stress Concentration: A Comparative Thermoelastic Stress Analysis with Normal Composite Femurs.

Proximal femoral fractures associated with osteoporosis are an important clinical problem, yet how bone quality independently influences stress distribution remains insufficiently understood. This study aimed to quantitatively compare surface stress distribution between normal and osteoporotic proximal femoral models using thermoelastic stress analysis (TSA). Fourth-generation composite femurs with identical external geometries were subjected to cyclic compressive loading at a 9° adduction angle, with different maximum loads applied to avoid structural failure (normal: 1900 N; osteoporotic: 1000 N). TSA was performed using an infrared lock-in system to obtain surface stress maps, and stress values were evaluated across key proximal regions and along the medial and lateral cortices. The osteoporotic group showed higher maximum stress values in the medial neck (-37.79 vs. -11.52 MPa), lateral neck (24.70 vs. 8.75 MPa), and intertrochanteric crest (-17.98 vs. -6.05 MPa), corresponding to approximately 1.8-3.5-fold increases compared with the normal model values normalized to 1000 N. Mean stress values were also higher by approximately 1.9-2.4-fold across regions. These results suggest that reduced bone quality is associated with increased proximal stress concentration. They may also help guide implant and fixation strategies, including stem selection and fixation configuration, by identifying regions susceptible to stress concentration under different bone quality conditions.