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

Lead Research Organisation: University of Sheffield
Department Name: Oncology and Metabolism

Abstract

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.

Planned Impact

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.
 
Description A testing jig has been developed and manufactured for performing for the first time a comprehensive analyses of the mechanical properties of the femoral head from osteoarthritic patients who underwent total hip replacement.
The jig allows us to perform in situ mechanical testing within a high-resolution micro computed tomography scanner that, combined with a state of the art digital volume correlation algorithm developed in my group, allowed us for the first time to evaluate the deformation of the whole femoral heads under compressive loading.
Moreover, we have developed an approach to measure morphometric parameters in several sub-regions of the femoral head that would allow us to find the correlation between the morphometric and mechanical properties in the bone.
Finally we are have developed a computational approach to estimate the deformation pattern in the femoral head under different loading scenarios that, once validated against the experiments performed in this study, will allow for the first time to relate the degree of disease with the mechanical properties and heterogeneous deformation of the femoral head. The validation is currently ongoing.
Exploitation Route The developed approaches have now to be applied to a large cohort of specimens from patients or cadavers with different degrees of osteoarthritis.
We are going to write a proposal for an EPSRC project soon,.
Sectors Healthcare

 
Description Effect of osteoarthritis on the chemical properties of the subchondral bone. 
Organisation University of Sheffield
Department Department of Materials Science and Engineering
Country United Kingdom 
Sector Academic/University 
PI Contribution This collaboration with Dr Ihtesham Rehman's group (we are co-supervising a PhD student together) focuses on the relationship between the morphometric, mechanical and chemical properties of the subchondral bone of patients with severe osteoarthritis. The specimens collected in this project have been scanned with micro computed tomography, mechanically tested in situ within the scanner and processed with the digital volume correlation approach in order to evaluate the full field of deformation.
Collaborator Contribution The collaborators will provide assessment of the chemical properties of the bone by using FTIR and Raman spectroscopy.
Impact the collaboration is multi-disciplinary between medicine, material science and image processing. No output have been produced yet.
Start Year 2017
 
Description Validation of finite element models for the human humerus by using digital volume correlation 
Organisation Western University
Country Canada 
Sector Academic/University 
PI Contribution The partners have performed mechanical tests of human humerus that we are processing with the digital volume correlation approach developed and updated during the project. The data will provide experimental measurements to be used to validate computational model of the human humerus for the prediction of structural and local mechanical properties.
Collaborator Contribution The partners (Dr Luis Ferrera's team) have performed mechanical tests of human humerus within an ex vivo microCT system that have been transferred to us for further analyses.
Impact We expect to have one or more publications in peer reviewed scientific journals once the data have been fully processed.
Start Year 2019
 
Description Validation of finite element models for the human scapula by using digital volume correlation. 
Organisation Western University
Country Canada 
Sector Academic/University 
PI Contribution Colleagues at the Western University (PI: Dr Louis Ferreira) have provided microCT images of the human scapula mechanically tested in situ within a scanning machine. The images of the specimens in undeformed and deformed configurations have been imported in our Digital Volume Correlation algorithm that provided the deformation and strain maps. The data have been sent to the collaborators for the comparison of the experimental data with predictions performed with different computational models of the scapula in order to understand the best modelling approach.
Collaborator Contribution The collaborators have prepared the specimens, performed the mechanical testing, acquired the images, processed the images, generated the finite element models and compared their outputs with the results provided by our algorithm.
Impact This collaboration is multi-disciplinary between medicine, engineering and image processing. The results are currently being analysed and will probably lead to two publications in international peer reviewed journals.
Start Year 2017