Défense de thèse de doctorat en sciences vétérinaires

Do specific magnetic resonance imaging and contrast enhanced computed tomography imaging provide early detection of cartilage changes after subchondral bone mechanical or chemical stimulation in an ovine model ?

Jury

Mandy PEFFERS (Univ. Liverpool), Sarah TAYLOR (Univ. Edimburgh), René VAN WEEREN (Univ. Utrecht), Peter CLEGG, promoteur (Univ. Liverpool), Simon TEW (Univ. Liverpool), Charles NICAISE, président (UNamur), Jean-Michel VANDEWEERD, promoteur (UNamur)

Résumé

Osteoarthritis is a concern in human and veterinary medicine since the progressive alteration of the joint components (i.e. cartilage, subchondral bone, synovium) is responsible for reduced joint function, quality-of-life, or performance. Due to the limited ability of appropriate self-repair of joint tissue, to the multiple structural and compositional changes that can occur, and the complexity of the OA process, it is important to better understand the early pathological processes and to better detect early structural and compositional changes that are associated to the disease.

In this context, this thesis aimed: (1) to compare magnetic resonance imaging (MRI) and computed tomography (CT) techniques in their ability to detect subtle cartilage structural changes; (2) to review the efficacy of MRI- and CT-based imaging techniques to identify compositional changes of cartilage; (3) to assess the efficacy of chemical or mechanical subchondral bone stimulation in inducing cartilage compositional or structural changes in an in vivo ovine model; (4) to test MRI T2 mapping and compositional CT to identify the early structural or compositional changes induced by subchondral bone stimulation.

This PhD thesis highlighted several perspectives for research and clinical applications. We demonstrated that the detection of cartilage defects was more accurate with CTA than MRI, ex vivo in the equine fetlock and in vivo in the ovine stifle. However, the requirement of general anaesthesia, the size of the specimen and the thickness of cartilage could sometimes limit the use of powerful MRI or CT scans in practice. In research, noninvasive baseline assessment of the joint should be part of the inclusion criteria. Compositional imaging techniques (T2 mapping and CECT) were unable to demonstrate a correlation with the subtle changes induced by chemical or mechanical stimulation. These techniques should be continuously improved since early noninvasive identification of joint changes is important for research and development of therapies. Finally, the main advantage of the subchondral bone insult model developed in this PhD thesis was the selective stimulation of the subchondral bone (without damages to the synovium, cartilage or ligaments), therefore limiting confusing factors such as synovitis. The histological differences between both types of stimulation may highlight two different mechanisms, one leading to pathology and the other to repair. This deserves to be investigated further to better understand how disease develops but also how subchondral bone stimulation can be useful.

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