Novel Assessment of the Osteoarthritic Hip Subchondral Bone: a Combined Experimental and Computational Investigation

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Osteoarthritis (OA) is a common disease that affects human joints, which degenerate over time. While OA is considered a disease mainly related to the cartilage, in fact major changes of the subchondral bone have been observed. In fact, we do not know yet if the degeneration starts from the bone or from the cartilage. Pathologic hip joints are really painful and can be fixed with a total hip replacement, a successful but invasive surgery during which parts of the femur and of the pelvis are replaced with prostheses. If we want to develop less invasive treatments (e.g. drug treatments or injectable biomaterials) it is fundamental to better understand the effect of OA to the joint tissues. In particular, we need to understand how the pathologic tissue deforms under loading. However, the complexity of such materials (bone and cartilage) makes the measurement of the relationship between their morphological properties and their mechanical response very hard to measure. The goal of this project is to use state of the art experimental, imaging and computational techniques to measure how the subchondral bone of the femoral head of osteoarthritic hips deforms under loading, underlining possible relationships between the bone microarchitecture and its failure behaviour. Since the recent development of digital image correlation techniques based on high-resolution images, there was no way to measure experimentally the 3D deformation of bone samples under load. Moreover, in order to estimate the failure behaviour of the same bone under different loading conditions, we need robust and accurate computational models, such as the micro finite element approach, applied to high-resolution images. During this project we will adapt the methodologies developed over the past years in my group to study the deformation of the subchondral bone in OA. We will use a recently acquired micro computed tomography (microCT) system for scanning the bones at high resolution, a custom made mechanical testing device that fits within the microCT for performing compress until failure the femoral heads, and a digital volume correlation (DVC) algorithm that can measure the three dimensional deformation of the bones. We will also generate state of the art computational models that can be validated with the DVC measurements and can be then used to estimate the deformation of the same bones under different loading scenarios. We already used a similar approach in my group to successfully validate the predictions of computational models for portions of trabecular bone. In this project we will adapt this procedure for analysing the behaviour of whole femoral head. By combining the obtained data we will be able to understand how osteoarthritis affects the morphometric, densitometric and mechanical properties of the subchondral bone of the femoral head. This information will help in the development of new implants and/or pharmacological interventions to treat osteoarthritic hip. Similar approaches can then be extended for other joints affected by OA.