Cationic agent contrast-enhanced computed tomography imaging of cartilage correlates with the compressive modulus and coefficient of friction

Objective: The aim of this study is to evaluate whether contrast-enhanced computed tomography (CECT) attenuation, using a cationic contrast agent (CA4+), correlates with the equilibrium compressive modulus (E) and coefficient of friction (mu) of ex vivo bovine articular cartilage. Methods: Correlations between CECT attenuation and E (Group 1, n = 12) and mu (Group 2, n = 10) were determined using 7 mm diameter bovine osteochondral plugs from the stifle joints of six freshly slaughtered, skeletally mature cows. The equilibrium compressive modulus was measured using a four-step, unconfined, compressive stress-relaxation test, and the coefficients of friction were determined from a torsional friction test. Following mechanical testing, samples were immersed in CA4+, imaged using mu CT, rinsed, and analyzed for glycosaminoglycan (GAG) content using the 1,9-dimethylmethylene blue (DMMB) assay. Results: The CECT attenuation was positively correlated with the GAG content of bovine cartilage (R-2 = 0.87, P < 0.0001 for Group 1 and R-2 = 0.74, P = 0.001 for Group 2). Strong and significant positive correlations were observed between E and GAG content (R-2 = 0.90, P < 0.0001) as well as CECT attenuation and E (R-2 = 0.90, P < 0.0001). The CECT attenuation was negatively correlated with the three coefficients of friction: CECT vs mu(static) (R-2 = 0.71, P = 0.002), CECT vs mu(static_equilibrium) (R-2 = 0.79, P < 0.001), and CECT vs mu(kinetic) (R-2 = 0.69, P = 0.003). Conclusions: CECT with CA4+ is a useful tool for determining the mechanical properties of ex vivo cartilage tissue as the attenuation significantly correlates with the compressive modulus and coefficient of friction. (C) 2012 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.