title: Computed tomography detects changes in contrast agent diffusion after collagen cross-linking typical to natural aging of articular cartilage.
abstract: OBJECTIVE
  The effect of threose-induced collagen cross-linking on the mechanical and diffusive properties of cartilage was investigated in vitro. In particular, we investigated the potential of Contrast Enhanced Computed Tomography (CECT) to detect changes in articular cartilage after increased collagen cross-linking, which is an age-related phenomenon.
  
  
  METHODS
  Osteochondral plugs (Ø=6.0 mm, n=28) were prepared from intact bovine patellae (n=7). Two of the four adjacent samples, prepared from each patella, were treated with threose to increase the collagen cross-linking, while the other two specimen served as paired controls. One sample pair was mechanically tested and then mechanically injured using a material testing device. Contrast agent [ioxaglate (Hexabrix™)] diffusion was imaged in the other specimen pair for 25 h using CECT. Water fraction, collagen and proteoglycan content, collagen network architecture and the amount of cross-links [hydroxylysyl pyridinoline (HP), lysyl pyridinoline (LP) and pentosidine (Pent)] of the samples were also determined.
  
  
  RESULTS
  Cartilage collagen cross-linking, both Pent and LP, were significantly (P<0.001) increased due to threose treatment. CECT could detect the increased cross-links as the contrast agent penetration and the diffusion flux were significantly (P<0.05) lower in the threose treated than in untreated samples. The equilibrium modulus (+164%, P<0.05) and strain dependent dynamic modulus (+47%, P<0.05) were both significantly greater in the threose treated samples than in reference samples, but there was no association between the initial dynamic modulus and the threose treatment. The water fraction, proteoglycan and collagen contents, as well as collagen architecture, were not significantly altered by the threose treatment.
  
  
  CONCLUSIONS
  To conclude, the CECT technique was found to be sensitive at detecting changes in cartilage tissue due to increased collagen cross-linking. This is important since increased cross-linking has been proposed to be related to the increased injury susceptibility of tissue.
authors.affiliation: Department of Applied Physics, University of Eastern Finland, Kuopio, Finland. harri.kokkonen@uef.fi
authors.forename: H T
authors.initials: HT
authors.lastname: Kokkonen
authors.forename: J
authors.initials: J
authors.lastname: Mäkelä
authors.forename: K A M
authors.initials: KA
authors.lastname: Kulmala
authors.forename: L
authors.initials: L
authors.lastname: Rieppo
authors.forename: J S
authors.initials: JS
authors.lastname: Jurvelin
authors.forename: V
authors.initials: V
authors.lastname: Tiitu
authors.forename: H M
authors.initials: HM
authors.lastname: Karjalainen
authors.forename: R K
authors.initials: RK
authors.lastname: Korhonen
authors.forename: V
authors.initials: V
authors.lastname: Kovanen
authors.forename: J
authors.initials: J
authors.lastname: Töyräs
mesh_terms: D000375:Aging / Q000502:physiology*; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives / Q000032:analysis; D002358:Cartilage, Articular / Q000737:chemistry / Q000000981:diagnostic imaging*; D016022:Case-Control Studies; D002417:Cattle; D003094:Collagen / Q000032:analysis / Q000737:chemistry*; D003287:Contrast Media; D006614:Hindlimb / Q000737:chemistry / Q000000981:diagnostic imaging; D007485:Ioxaglic Acid; D008239:Lysine / Q000031:analogs & derivatives / Q000032:analysis; D010329:Patella / Q000737:chemistry / Q000000981:diagnostic imaging*; D013780:Tetroses; D014057:Tomography, X-Ray Computed / Q000379:methods
chemical_list: D000596:Amino Acids; D003287:Contrast Media; D013780:Tetroses; C015484:pyridinoline; C036020:deoxypyridinoline; D003094:Collagen; D001120:Arginine; C062187:pentosidine; D008239:Lysine; C073321:erythrose; D007485:Ioxaglic Acid