Abstract
The biochemical and histopathological techniques used to investigate meniscal content and structure are destructive and time-consuming. Therefore, this study evaluated whether contrast-enhanced computed tomography (CECT) attenuation and contrast agent flux using the iodinated contrast agents CA4+ and ioxaglate correlate with the glycosaminoglycan (GAG) content/distribution and water content in human menisci. The optimal ioxaglate and CA4+ contrast agent concentrations for mapping meniscal GAG distribution were qualitatively determined by comparison of CECT color maps with Safranin-O stained histological sections. The associations between CECT attenuation and GAG content, CECT attenuation and water content, and flux and water content at various time points were determined using both contrast agents. Depth-wise analyses were also performed through each of the native surfaces to examine differences in contrast agent diffusion kinetics and equilibrium partitioning. The optimal concentrations for GAG depiction for ioxaglate and CA4+ were ≥80 and 12 mgI/ml, respectively. Using these concentrations, weak to moderate associations were found between ioxaglate attenuation and GAG content at all diffusion time points (1-48 h), while strong and significant associations were observed between CA4+ attenuation and GAG content as early as 7 h (R2 ≥ 0.67), being strongest at the equilibrium time point (48 h, R2 = 0.81). CECT attenuation for both agents did not significantly correlate with water content, but CA4+ flux correlated with water content (R2 = 0.56-0.64). CECT is a promising, non-destructive imaging technique for ex vivo assessment of meniscal GAG concentration and water content compared to traditional biochemical and histopathological methods. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1018-1028, 2017.
Highlights
Meniscus and Osteoarthritis: The human menisci are semilunar-shaped, weight-bearing fibrocartilaginous tissues [1]
Various collagen types are present in the meniscus, including Type I [1], which typically has the highest concentration, and Types II, III, V, and VI [1]. They are arranged in internal bundles and tangentially to the tissue surfaces, providing the meniscus the ability to overcome the tensile and shear forces during locomotion, while the internal proteoglycans and their associated glycosaminoglycans (GAGs) hydrogen bond to water to confer meniscal tissue its compressive strength [2, 3]
Once thawing of each meniscus was complete overnight at 4o C, the non-native surfaces were sealed with cyanoacrylate glue to prevent contrast agent from diffusing through these surfaces. This would account for the fact that slicing the meniscus would artificially create non-native surfaces. This experiment consisted of three studies 1) a diffusion-in study to determine the time required for the cationic contrast agent (CA4+) to reach equilibrium, 2) an optimization study to determine the optimal concentration for CA4+ and ioxaglate by qualitatively comparing the ability of various concentrations of both agents to map the GAG distribution in human menisci at equilibrium, and 3) a fixed-concentration study a) to compare the contrast-enhanced computed tomography (CECT) attenuation at different time points to tissue GAG and water contents and b) to compare the time-dependent contrast agent fluxes through each native surface to tissue water content
Summary
Meniscus and Osteoarthritis: The human menisci are semilunar-shaped, weight-bearing fibrocartilaginous tissues [1] Their function is to reduce friction in the knee joint, absorb shock, protect the articular cartilage from excessive stress during daily activities, and they are principally composed of water (7075% by mass), collagens (20-25%), and proteoglycans (1-2%) [2, 3]. Various collagen types are present in the meniscus, including Type I [1], which typically has the highest concentration, and Types II, III, V, and VI [1] They are arranged in internal bundles and tangentially to the tissue surfaces, providing the meniscus the ability to overcome the tensile and shear forces during locomotion, while the internal proteoglycans and their associated glycosaminoglycans (GAGs) hydrogen bond to water to confer meniscal tissue its compressive strength [2, 3]. Lower compressive and dynamic moduli are indicative of the cartilage’s loss of ability to maintain structural integrity
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