Relationship between bone material property distribution and stress distribution in femurs after THA

抄録

Bone material properties in the femur exhibit marked spatial heterogeneity, which may influence stress distribution after total hip arthroplasty (THA). However, many finite element (FE) studies have relied on homogeneous material assumptions, potentially overlooking patient-specific femoral mechanical behavior. The objectives of this study were to investigate the influence of heterogeneous bone material properties on stress distribution in THA femurs and to clarify the relationship between local bone stiffness and stress distribution across Gruen zones. Subject-specific FE models of three femurs with different Dorr classifications (A-C) were constructed using computed tomography (CT) images. Heterogeneous material properties were assigned based on Hounsfield unit-derived density and elastic modulus, and two cementless stem designs (short and long stems) were analyzed under physiological walking loads. Average von Mises stress was evaluated in each Gruen zone and compared with composite elastic modulus calculated using a rule-of-mixtures approach. The results showed that overall stress distribution patterns were qualitatively similar to those obtained using homogeneous material models, exhibiting stress shielding and distal stress concentration regardless of stem type or femoral morphology. However, within the same Gruen zones, an inverse relationship was observed between composite elastic modulus and average von Mises stress, particularly in mid-to-distal regions. Compared with homogeneous models, heterogeneous models exhibited lower stress magnitudes due to reduced bending deformation. These findings indicate that while homogeneous models may be sufficient for comparative parametric analyses, heterogeneous material modeling provides important insights into local stress-stiffness relationships and patient-specific bone quality. Incorporating material heterogeneity is considered essential for accurate prediction of local mechanical behavior and for future simulations of bone remodeling and fracture risk after THA.