Maturation of collagen fibril network structure in tibial and femoral cartilage of rabbits

Objective: The structure and composition of articular cartilage change during development and growth, as well as in response to varying loading conditions. These changes modulate the functional properties of cartilage. We studied maturation-related changes in the collagen network organization of cartilage as a function of tissue depth. Design: Articular cartilage from the tibial medial plateaus and femoral medial condyles of female New Zealand white rabbits was collected from six age-groups: 4 weeks (n = 30), 6 weeks (n = 30), 3 months (n = 24), 6 months (n = 24), 9 months (n = 27) and 18 months (n = 19). Collagen fibril orientation, parallelism (anisotropy) and optical retardation were analyzed with polarized light microscopy. Differences in the development of depth-wise collagen organization in consecutive age-groups and the two joint locations were compared statistically. Results: The collagen fibril network of articular cartilage undergoes significant changes during maturation. The most prominent changes in collagen architecture, as assessed by orientation, parallelism and retardation were noticed between the ages of 4 and 6 weeks in tibial cartilage and between 6 weeks and 3 months in femoral cartilage, i.e., orientation became more perpendicular-to-surface, and parallelism and retardation increased with changes being most prominent in the deep zone. At the age of 6 weeks, tibial cartilage had a more perpendicular-to-surface orientation in the middle and deep zones than femoral cartilage (P < 0.001) and higher parallelism throughout the tissue depth (P < 0.001), while femoral cartilage exhibited more parallel-to-surface orientation (P < 0.01) above the deep zone after maturation. Optical retardation of collagen was higher in tibial than in femoral cartilage at the ages of 4 and 6 weeks (P < 0.001), while at older ages, retardation below the superficial zone in the femoral cartilage became higher than in the tibial cartilage. Conclusions: During maturation, there is a significant modulation of collagen organization in articular cartilage which occurs earlier in tibial than in femoral cartilage, and is most pronounced in the deep zone. (C) 2009 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.