MATURATION-RELATED COMPRESSIVE PROPERTIES OF RABBIT KNEE ARTICULAR-CARTILAGE AND VOLUME FRACTION OF SUBCHONDRAL TISSUE

Objective: Knowledge about the physiologic change in cartilage biomech anics, accompanying the structural remodeling of the cartilage bone un it during maturation, may have relevance to understand the development of joint disease. The purpose of this study was to investigate matura tion-dependent changes of compressive properties of articular cartilag e and volume fraction of subchondral tissue in healthy rabbit knees. M ethods: Cartilage compressive properties (instantaneous and creep modu li) were tested at seven defined knee joint regions of five young (ten weeks), five adolescent (eighteen weeks) and five adult (above thirty -one weeks) healthy rabbits with in-situ indentation tests. Morphometr ic analysis of volume fraction of subchondral tissue was carried out a t four regions. Results: Cartilage stiffness (instantaneous modulus) d ecreased between infancy and adolescence (P < 0.009), and stayed then the same. A simultaneous significant change in (50-second) creep modul us was only observed at one region, but both moduli correlated to each other. Subchondral tissue consisted of cancellous bone in the young., and formed a more solid bone plate not before adolescence. Its volume fraction increased from infancy to adolescence (P < 0.001), but staye d then the same. There was a significant inverse correlation between t he volume fraction of subchondral tissue and cartilage stiffness at th e four measured regions (R-2 = -0.59). The arrangement of collagen fil er bundles in the deeper cartilage layers changed from a mesh-like str ucture in the young to a more perpendicular alignment in the adolescen t and adult. Conclusion: The maturation-related change in compressive properties coincided with a conspicuous change in volume fraction of t he subchondral tissue. The main change appeared around puberty.