Dual‐contrast micro‐CT enables cartilage lesion detection and tissue condition evaluation ex vivo

BACKGROUND: Post‐traumatic osteoarthritis is a frequent joint disease in the horse. Currently, equine medicine lacks effective methods to diagnose the severity of chondral defects after an injury. OBJECTIVES: To investigate the capability of dual‐contrast‐enhanced computed tomography (dual‐CECT) for detection of chondral lesions and evaluation of the severity of articular cartilage degeneration in the equine carpus ex vivo. STUDY DESIGN: Pre‐clinical experimental study. METHODS: In nine Shetland ponies, blunt and sharp grooves were randomly created (in vivo) in the cartilage of radiocarpal and middle carpal joints. The contralateral joint served as control. The ponies were subjected to an 8‐week exercise protocol and euthanised 39 weeks after surgery. CECT scanning (ex vivo) of the joints was performed using a micro‐CT scanner 1 hour after an intra‐articular injection of a dual‐contrast agent. The dual‐contrast agent consisted of ioxaglate (negatively charged, q = −1) and bismuth nanoparticles (BiNPs, q = 0, diameter ≈ 0.2 µm). CECT results were compared to histological cartilage proteoglycan content maps acquired using digital densitometry. RESULTS: BiNPs enabled prolonged visual detection of both groove types as they are too large to diffuse into the cartilage. Furthermore, proportional ioxaglate diffusion inside the tissue allowed differentiation between the lesion and ungrooved articular cartilage (3 mm from the lesion and contralateral joint). The mean ioxaglate partition in the lesion was 19 percentage points higher (P < 0.001) when compared with the contralateral joint. The digital densitometry and the dual‐contrast CECT findings showed good subjective visual agreement. MAIN LIMITATIONS: Ex vivo study protocol and a low number of investigated joints. CONCLUSIONS: The dual‐CECT methodology, used in this study for the first time to image whole equine joints, is capable of effective lesion detection and simultaneous evaluation of the condition of the articular cartilage.