Contribution of Bone Tissue Properties to Strength of the Ageing Human Hip

SNF grant # 200365 with PSI and EMPA.
Today, we are facing rapid ageing of the world population, which increases the incidence of hip fractures. In clinics, the recent method to assess bone strength is homogenized FEA (hFEA) constructed from QCT reconstructions. Despite considerable evidence of degradation of bone material properties with age, in the past fifty years of FEA, bone material parameters to predict bone strength remained independent of age. This project aims to assess the influence of age on the mechanical integrity of both, mineral and organic phases of the human proximal femur. Using an inverse method, the hypothesis that FEA material parameters are independent of age was tested. Eighty-six human femora were scanned, QCT-based hFEA bone strength predictions and μCT-based μFEA analysis with the femoral sections compressed until failure were compared. The errors between the simulation and the experiment for apparent modulus, yield stress, and strength were age-independent, suggesting no rationale for correcting tissue material parameters in the current FEA of the ageing femoral neck. Additionally, eighty samples were demineralized and tested in tension until failure. It has been shown that mechanical integrity of the collagen network deteriorates with increasing age and may lead to decreased post-yield properties of aged bone.

The ultimate strength of demineralised bone samples tested in tension (a, left) decreases with age (b, right) independently of bone volume fraction.

Biomechanical Stability of Bone Screws in the Proximal Humerus

with AO.
Proximal humerus fractures (PHF) are among the third most common injuries related to osteoporosis. In this thesis, the failure mechanism of PHF treated with locking plates was investigated by testing the propagation of single screws in human bone samples under cyclic loading. With micro finite element simulations and an analytical model, it was possible to qualitatively describe the experiments. These findings might be a step towards defining the optimal treatment for patients suffering from a PHF.

Biomechanical Testing and Simulation 

with ZMK.
Various strategies are currently debated in dental implantology to improve primary stability of dental implants, especially from the perspective of cost-effective, immediate loading procedures. The biomechanics laboratory offers an experimental protocol, but also computational models of the bone-implant interface based on μCT reconstructions, to quantify primary stability in human or bovine alveolar bone for different drilling protocols and implant designs.