Magnetic resonance microimaging (micro-MRI) is a well-established tool for joint imaging, and in particular for the imaging of animal models of joint diseases such as osteoarthritis.
Post-traumatic osteoarthritis (PTOA) is often triggered by knee injury. It affects articular cartilage (AC), subchondral bone, meniscus and the synovial membrane of the knee. The available treatments for PTOA are currently largely ineffective due to late diagnosis past the “treatment window”. This study aimed to develop a detailed understanding of the time line of the progression of PTOA in murine models through longitudinal observation of the femorotibial joint from the onset of the disease to the advanced stage. Quantitative micro-MRI and histology were used to evaluate PTOA-associated changes in the knee joints of rats subjected to knee meniscectomy.
Systematic longitudinal changes in the articular cartilage thickness, cartilage T2 and the relative volume of cortical bone within the tibial epiphysis were all found to be associated with the development of PTOA in the animals. The following pathogenesis cascade was found to precede advanced PTOA: meniscal injury → AC swelling → subchondral bone remodelling → proteoglycan depletion → free water influx → cartilage erosion.
Our findings demonstrate that MRI properties of the subchondral bone (as well as articular cartilage) can potentially serve as biomarkers of PTOA. Importantly, the imaging protocol used in this study was entirely MRI-based and therefore did not involve ionising radiation. This protocol is suitable for whole-knee longitudinal, non-invasive assessment of the development of OA in-vivo. The results of this work will inform the improvement of the imaging methods for early diagnosis of PTOA, as well as improve the understanding of physiological mechanisms underpinning the development of osteoarthritis.