Assessment of contrast-enhanced computed tomography for imaging of cartilage during fracture healing

Assessment of the early stages of fracture healing via X-rays and computed tomography is limited by the low radio-opacity of cartilage. We validated a method of contrast-enhanced computed tomography (CECT) for non-destructive identification of cartilage within a healing fracture callus. Closed, stabilized fractures in femora of C57BL/6 mice were harvested on post-operative day 9.5 and imaged ex vivo with micro-computed tomography (µCT) before and after incubation in a cationic contrast agent that preferentially accumulates in cartilage due to the high concentration of sulfated glycosaminoglycans in the tissue. Co-registration of the pre- and post-incubation images, followed by image subtraction, enabled two- and three-dimensional delineation of mineralized tissue, soft callus, and cartilage. The areas of cartilage and callus identified with CECT were compared to those identified with the gold-standard method of histomorphometry. No difference was found between the areas of cartilage measured by the two methods (p = 0.999). Callus area measured by CECT was smaller than, but strongly predictive of (R(2) = 0.80, p < 0.001), the corresponding histomorphometric measurements. CECT also enabled qualitative identification of mineralized cartilage. These findings indicate that the CECT method provides accurate, quantitative, and non-destructive visualization of the shape and composition of the fracture callus, even during the early stages of repair when little mineralized tissue is present. The non-destructive nature of this method would allow subsequent analyses, such as mechanical testing, to be performed on the callus, thus enabling higher-throughput, comprehensive investigations of bone healing.