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

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.

Knowledge. The results of the project will increase our knowledge in different research fields. We will improve our understanding of how osteoarthritis affects the mechanics of the hip joint and in particular of the subchondral bone in the femoral heads. The impact will be reached by the dissemination of the results with publications in international journals, attending conferences and giving seminars. The datasets will be shared in the public domain and made available for the interested researchers worldwide raising the UK profile in this research area. We will also extend the applicability of digital volume correlation (DVC) techniques for the analyses of large datasets. Our DVC approach was found to be the most accurate among the ones presented so far in the literature so to generate impact around this technique we will create an online service accessible to external users who could use it for similar applications.

People. With this project Dr Dall'Ara will strengthen his position as independent researcher, increasing his group and giving the opportunity to the appointed PDRA to work in a stimulating multidisciplinary research environment. Dr Dall'Ara will train the PDRA in experimental and computational biomechanics, with particular emphasis to the required validation study.

Economy. The long-term beneficiaries of the study will be the manufacturers of orthopaedic devices and biomaterials to treat osteoarthritic hips as well drug companies which aim to develop pharmacological treatments for OA patients. Moreover, the applicant will be in continuous contact with the developers of image processing (Simpleware, Materialize, FEI software) and finite element modelling (Ansys and Simulia) software packages for potential future development. Moreover, contacts will be kept with the manufacturer of the scanning device used in the experiments (Scanco) in order to evaluate potential interests in commercialising the designed testing device for in situ experiments.

Society. The results obtained in this study will improve our understanding of the pathophysiology of OA and help the design of targeted interventions, which in the long term could be beneficial for the NHS and therefore patients.