Simultaneous computed tomography of articular cartilage and subchondral bone.

Objective: Contrast agent enhanced computed tomography (CECT) may be used to detect depletion of superficial proteoglycans in articular cartilage. In principle, computed tomography can also be used to diagnose the state of subchondral bone. Because osteoarthritis affects both cartilage and bone, we aimed to evaluate the feasibility of the CECT to simultaneously assess the state of these tissues. Further, we studied the spatial variation of contrast agent content in the CECT, properties of subchondral bone and the mechanical stiffness of articular cartilage across the bovine medial tibial plateau.

Methods: Osteochondral samples (n=10) were prepared from fresh and visually intact bovine medial tibial plateaus. The dynamic mechanical modulus of the samples was measured using an arthroscopic indentation device. Subsequently, the samples were scanned with a peripheral quantitative computed tomography (pQCT) device prior to and after 35.5h of immersion in an anionic iodinated contrast agent, (ioxaglate) solution. The thickness of the cartilage was measured with ultrasound and pQCT.

Results: In the medial tibial plateau, the site-dependent variation in the dynamic modulus, thickness of the cartilage, thickness of the subchondral plate and contrast agent content in the superficial cartilage was statistically significant (P<0.01). The linear correlation between the superficial contrast agent content and the dynamic modulus was rho=-0.80 (P<0.01).

Discussion: The CECT enabled simultaneous analysis of the contrast agent penetration into cartilage, cartilage thickness and subchondral bone density and thickness. The contrast agent content in cartilage depends on the composition and structure of the tissue. Thereby the CECT also provided indirect information on the mechanical properties of the tissue, analogously to the dGEMRIC. Thus, the CECT may provide means to diagnose simultaneously the integrity of cartilage and subchondral bone in vivo.