Contrast-enhanced X-ray imaging of articular cartilage: reliability of a cationic contrast agent in combination with high-resolution peripheral quantitative computed tomography system

Articular cartilage showcases distinctive mechanical behaviour, attributable to its biphasic composition and hierarchical organization. Proteoglycans, essential constituents of the extracellular matrix, contribute to tissue swelling, stiffness, and viscoelasticity, thanks to the fixed charge density. Degenerative alterations in proteoglycan content and collagen structure - key indicators of diseases such as osteoarthritis - compromise the mechanical integrity of articular cartilage, underscoring the importance of early detection. Although magnetic resonance imaging provides valuable compositional information, its limited spatial resolution restricts its effectiveness in evaluating thin soft tissues such as articular cartilage. As an alternative, contrast-enhanced X-ray imaging circumvents such limitation, resorting to the use of radiopaque contrast agents. In this context, cationic contrast agents, like CA4+, enable the quantitative assessment of proteoglycan content via electrostatic attraction. High-resolution peripheral quantitative computed tomography offers an optimal compromise between spatial resolution and radiation exposure, making it a promising tool for clinical use. This study aimed to explore the relationship between proteoglycan content - quantified through contrast-enhanced high-resolution peripheral quantitative computed tomography combined with the use of CA4+ - and the viscoelastic properties of healthy bovine articular cartilage, assessed via indentation testing. Results highlighted significant correlations between the enhanced radiopacity of articular cartilage, ascribable to the PG content, with parameters representing the mechanical response of the tissue.