Contrast enhanced µCT imaging of early articular changes in a pre-clinical model of osteoarthritis.

OBJECTIVE: The objective of this study was to characterize early osteoarthritis (OA) development in cartilage and bone tissues in the rat medial meniscus transection (MMT) model using non-destructive equilibrium partitioning of an ionic contrast agent micro-computed tomography (EPIC-µCT) imaging. Cartilage fibrillation, one of the first physiological developments in OA, was quantified in the rat tibial plateau as three-dimensional (3D) cartilage surface roughness using a custom surface-rendering algorithm. METHODS: Male Lewis rats underwent MMT or sham-operation in the left leg. At 1- and 3-weeks post-surgery, the animals (n = 7-8 per group) were euthanized and the left legs were scanned using EPIC-µCT imaging to quantify cartilage and bone parameters. In addition, a custom algorithm was developed to measure the roughness of 3D surfaces. This algorithm was validated and used to quantify cartilage surface roughness changes as a function of time post-surgery. RESULTS: MMT surgery resulted in significantly greater cartilage damage and subchondral bone sclerosis with the damage increasing in both severity and area from 1- to 3-weeks post-surgery. Analysis of rendered 3D surfaces could accurately distinguish early changes in joints developing OA, detecting significant increases of 45% and 124% in surface roughness at 1- and 3-weeks post-surgery respectively. CONCLUSION: Disease progression in the MMT model progresses sequentially through changes in the cartilage articular surface, extracellular matrix composition, and then osteophyte mineralization and subchondral bone sclerosis. Cartilage surface roughness is a quantitative, early indicator of degenerative joint disease in small animal OA models and can potentially be used to evaluate therapeutic strategies.

Quantitative pre-clinical screening of therapeutics for joint diseases using contrast enhanced micro-computed tomography.

OBJECTIVE: The development of effective therapies for cartilage protection has been limited by a lack of efficient quantitative cartilage imaging modalities in pre-clinical in vivo models. Our objectives were two-fold: first, to validate a new contrast-enhanced 3D imaging analysis technique, equilibrium partitioning of an ionic contrast agent-micro computed tomography (EPIC-µCT), in a rat medial meniscal transection (MMT) osteoarthritis (OA) model; and second, to quantitatively assess the sensitivity of EPIC-µCT to detect the effects of matrix metalloproteinase inhibitor (MMPi) therapy on cartilage degeneration. METHODS: Rats underwent MMT surgery and tissues were harvested at 1, 2, and 3 weeks post-surgery or rats received an MMPi or vehicle treatment and tissues harvested 3 weeks post-surgery. Parameters of disease progression were evaluated using histopathology and EPIC-µCT. Correlations and power analyses were performed to compare the techniques. RESULTS: EPIC-µCT was shown to provide simultaneous 3D quantification of multiple parameters, including cartilage degeneration and osteophyte formation. In MMT animals treated with MMPi, OA progression was attenuated, as measured by 3D parameters such as lesion volume and osteophyte size. A post-hoc power analysis showed that 3D parameters for EPIC-µCT were more sensitive than 2D parameters requiring fewer animals to detect a therapeutic effect of MMPi. 2D parameters were comparable between EPIC-µCT and histopathology. CONCLUSION: This study demonstrated that EPIC-µCT has high sensitivity to provide 3D structural and compositional measurements of cartilage and bone in the joint. EPIC-µCT can be used in combination with histology to provide a comprehensive analysis to screen new potential therapies.

Localized 3D analysis of cartilage composition and morphology in small animal models of joint degeneration.

OBJECTIVE: Current histological scoring methods to evaluate efficacy of potential therapeutics for slowing or preventing joint degeneration are time-consuming and semi-quantitative in nature. Hence, there is a need to develop and standardize quantitative outcome measures to define sensitive metrics for studying potential therapeutics. The objectives of this study were to use equilibrium partitioning of an ionic contrast agent via Equilibrium Partitioning of an Ionic Contrast-Microcomputed tomography (EPIC-µCT) to quantitatively characterize morphological and compositional changes in the tibial articular cartilage in two distinct models of joint degeneration and define localized regions of interest to detect degenerative cartilage changes. MATERIALS AND METHODS: The monosodium iodoacetate (MIA) and medial meniscal transection (MMT) rat models were used in this study. Three weeks post-surgery, tibiae were analyzed using EPIC-µCT and histology. EPIC-µCT allowed measurement of 3D morphological changes in cartilage thickness, volume and composition. RESULTS: Extensive cartilage degeneration was observed throughout the joint in the MIA model after 3 weeks. In contrast, the MMT model showed more localized degeneration with regional thickening of the medial tibial plateau and a decrease in attenuation consistent with proteoglycan (PG) depletion. Focal lesions were also observed and 3D volume calculated as an additional outcome metric. CONCLUSIONS: EPIC-µCT was used to quantitatively assess joint degeneration in two distinct preclinical models. The MMT model showed similar features to human Osteoarthritis (OA), including localized lesion formation and PG loss, while the MIA model displayed extensive cartilage degeneration throughout the joint. EPIC-µCT imaging provides a rapid and quantitative screening tool for preclinical evaluation of OA therapeutics.