Maturation-related compressive properties of rabbit knee articular cartilage and volume fraction of subchondral tissue.

OBJECTIVE: Knowledge about the physiologic change in cartilage biomechanics, accompanying the structural remodeling of the cartilage bone unit during maturation, may have relevance to understand the development of joint disease. The purpose of this study was to investigate maturation-dependent changes of compressive properties of articular cartilage and volume fraction of subchondral tissue in healthy rabbit knees.
METHODS: Cartilage compressive properties (instantaneous and creep moduli) 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. Morphometric analysis of volume fraction of subchondral tissue was carried out at four regions.
RESULTS: Cartilage stiffness (instantaneous modulus) decreased between infancy and adolescence (P < 0.009), and stayed then the same. A simultaneous significant change in (50-second) creep modulus 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 stayed then the same. There was a significant inverse correlation between the volume fraction of subchondral tissue and cartilage stiffness at the four measured regions (R2 = -0.59). The arrangement of collagen fiber bundles in the deeper cartilage layers changed from a mesh-like structure in the young to a more perpendicular alignment in the adolescent and adult.
CONCLUSION: The maturation-related change in compressive properties coincided with a conspicuous change in volume fraction of the subchondral tissue. The main change appeared around puberty.