Dual-contrast computed tomography enables detection of equine posttraumatic osteoarthritis in vitro

To prevent the progression of posttraumatic osteoarthritis, assessment of cartilage composition is critical for effective treatment planning. Posttraumatic changes include proteoglycan (PG) loss and elevated water content. Quantitative dual-energy computed tomography (QDECT) provides a means to diagnose these changes. Here, we determine the potential of QDECT to evaluate tissue quality surrounding cartilage lesions in an equine model, hypothesizing that QDECT allows detection of posttraumatic degeneration by providing quantitative information on PG and water contents based on the partitions of cationic and nonionic agents in a contrast mixture. Posttraumatic osteoarthritic samples were obtained from a cartilage repair study in which full-thickness chondral defects were created surgically in both stifles of seven Shetland ponies. Control samples were collected from three nonoperated ponies. The experimental (n = 14) and control samples (n = 6) were immersed in the contrast agent mixture and the distributions of the agents were determined at various diffusion time points. As a reference, equilibrium moduli, dynamic moduli, and PG content were measured. Significant differences (p < 0.05) in partitions between the experimental and control samples were demonstrated with cationic contrast agent at 30 min, 60 min, and 20 h, and with non-ionic agent at 60 and 120 min. Significant Spearman's rank correlations were obtained at 20 and 24 h (rho = 0.482-0.693) between the partition of cationic contrast agent, cartilage biomechanical properties, and PG content. QDECT enables evaluation of posttraumatic changes surrounding a lesion and quantification of PG content, thus advancing the diagnostics of the extent and severity of cartilage injuries

Quantitative evaluation of knee subchondral bone mineral density using cone beam computed tomography

Contrast agent enhanced cone beam computed tomography (CE-CBCT), a technique capable of high-resolution in vivo imaging with small radiation dose, has been applied successfully for clinical diagnostics of cartilage degeneration, i.e., osteoarthritis (OA). As an X-ray technique, CE-CBCT may also detect changes in mineral density of subchondral bone (volumetric bone mineral density, vBMD), known to be characteristic for OA. However, its feasibility for density measurements is not clear due to limited signal-to-noise ratio and contrast of CBCT images. In the present study, we created clinically applicable hydroxyapatite phantoms and determined vBMDs of cortical bone, trabecular bone, subchondral trabecular bone and subchondral plate of 10 cadaver (ex vivo) and 10 volunteer (in vivo) distal femora using a clinical CBCT scanner, and for reference, also using a conventional CT scanner. Our results indicated strong linear correlations between the vBMD values measured with the CT and CBCT scanners (R > 0.90, p < 0.001), however, absolute vBMD values were dependent on the scanner in use. Further, the differences between the vBMDs of cortical bone, trabecular bone and subchondral bone were similar and independent of the scanner. The present results indicate that vBMD values might not be directly comparable between different instruments. However, based on our present and previous results, we propose that, for OA diagnostics, clinical CBCT enables not only quantitative analysis of articular cartilage but also subchondral bone vBMD. Quantitative information on both cartilage and subchondral bone could be beneficial in OA diagnostics