title: Cationic agent contrast-enhanced computed tomography imaging of cartilage correlates with the compressive modulus and coefficient of friction.
abstract: 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 (μ) of ex vivo bovine articular cartilage.
  
  
  METHODS
  Correlations between CECT attenuation and E (Group 1, n = 12) and μ (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 μCT, 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 μ(static) (R(2) = 0.71, P = 0.002), CECT vs μ(static_equilibrium) (R(2) = 0.79, P < 0.001), and CECT vs μ(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.
authors.affiliation: Center for Advanced Orthopaedic Studies, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, United States.
authors.forename: B A
authors.initials: BA
authors.lastname: Lakin
authors.forename: D J
authors.initials: DJ
authors.lastname: Grasso
authors.forename: S S
authors.initials: SS
authors.lastname: Shah
authors.forename: R C
authors.initials: RC
authors.lastname: Stewart
authors.forename: P N
authors.initials: PN
authors.lastname: Bansal
authors.forename: J D
authors.initials: JD
authors.lastname: Freedman
authors.forename: M W
authors.initials: MW
authors.lastname: Grinstaff
authors.forename: B D
authors.initials: BD
authors.lastname: Snyder
mesh_terms: D000818:Animals; D002358:Cartilage, Articular / Q000000981:diagnostic imaging* / Q000502:physiology; D002417:Cattle; D019245:Compressive Strength / Q000502:physiology*; D003287:Contrast Media; D055119:Elastic Modulus / Q000502:physiology*; D017276:Friction; D006025:Glycosaminoglycans / Q000032:analysis*; D013264:Stifle / Q000000981:diagnostic imaging; D013314:Stress, Mechanical; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D003287:Contrast Media; D006025:Glycosaminoglycans