Philippe K. Zysset's KTH Solid Mechanics KEYNOTE Seminar "Multiscale Bone Mechanics: From the Bench to the Bedside"

philippe.zysset_March_21_2024.pdf (pdf 276 kB)

Abstract. Osteoporosis is a metabolic bone disease characterized by a reduction of bone quantity and strength that results in low-energy fractures. Despite long-term research efforts, it remains unclear whether bone quality also contributes substantially to bone fragility. Bone is a multiscale composite made of mineral, collagen, and water that exhibits anisotropic viscoelasticity as well as diffuse cracking at the nanoscale and linear cracking at the micro scale along both shear and tensile overloading. Interestingly, opening of these cracks produce residual deformations at the microscale with coupled reduction in elastic modulus at the macroscale. This anisotropic, time-dependent, and non-linear behaviour of bone can be modelled in the frame of standard generalised materials to compute yield strength by finite element (FE) analysis from quantitative computed tomography (QCT) reconstructions. From a clinical perspective, the development of 2D-3D reconstructions of dual x-ray absorptiometry (DXA) images enables FE analyses of the proximal femur in a sideways fall and the establishment of a unified criterion with opportunistic QCT-based FE for fragile, low, and normal bone strength. Alternatively, high-resolution peripheral computed tomography (HR-pQCT) offers a distinct evaluation of trabecular and cortical bone structural integrity. Finally, the actual fracture risk of a bone is derived from conditional probabilities of falling, hitting the ground severely and presenting insufficient strength