Clark J M, Norman A, Nötzli H
University of Washington, Seattle 98195, USA.
J Anat. 1997 Aug;191 ( Pt 2)(Pt 2):215-21. doi: 10.1046/j.1469-7580.1997.19120215.x.
Changes in the 3-dimensional arrangement of the articular cartilage matrix during growth of the rabbit tibial plateau were studied. Knees from newborn, and 1, 2 and 6 wk-old rabbits were compared with those of adults by light and electron microscopy. The specimens were fixed, embedded en bloc in epoxy resin and sectioned vertically/coronally through the point where the articular cartilage was thickest in the adult medial tibial plateau. At birth, the proximal tibial epiphysis was cartilaginous, but nascent articular cartilage was recognisable as a densely cellular layer covering the tibial condyle. Within 30 microns of the articular surface, the chondrocytes were flattened and collagen fibres ran among these cells in a direction parallel to the surface. Deeper in the articular cartilage, rounded cells were evenly distributed within a random collagen fibril network. At the centre of the plateau, the tangential layer changed little during growth, whereas the subjacent cellular layer grew in thickness and steadily achieved a more vertical character in the organisation of its constituent collagen and cellular elements. At 1 wk, cells were separated into clusters by acellular regions filled with collagen fibrils. At 2 wk, cells within the forming radial zone were aligned in columns bracketed by vertical collagen fibres. Continuity of these vertical fibres with those in the tangential surface layer was evident at this age. The chondrocytes were surrounded by fibrous capsules typical of chondrons. By 6 wk, the bases of the radial collagen fibres in the very centre of the condyle had calcified, as had the adjacent hypertrophic hyaline cartilage. A solid subchondral plate and tidemark did not appear until skeletal maturity. From birth to age 6 wk, maximum thickness of the layer identified as primordial articular cartilage increased from 0.13 mm to 0.70 mm, and was 1.5 mm in the adult. Throughout growth, however, the thickness of the tangential layer in the centre of the plateau never exceeded 0.05 micron. In the patella, femoral head and peripheral tibial plateau, cartilage development followed the same general sequence. In contrast to the central tibial plateau, the tangential layer also grew in thickness, but at a slower rate than that of the radial zone. At all ages, the developing articular cartilage was structurally distinct from the deeper hyaline cartilage which contributed to growth of the ossification centre through enchondral ossification. The collagen matrix of articular cartilage acquires a characteristic, orderly 3-dimensional structure soon after birth. Growth in cartilage thickness occurs primarily through enlargement of the radial zone.
研究了兔胫骨平台生长过程中关节软骨基质三维排列的变化。通过光镜和电镜将新生兔、1周龄、2周龄和6周龄兔的膝关节与成年兔的膝关节进行比较。标本固定后，整体包埋于环氧树脂中，并在成年内侧胫骨平台关节软骨最厚处垂直/冠状切片。出生时，胫骨近端骨骺为软骨，但新生关节软骨可识别为覆盖胫骨髁的致密细胞层。在关节表面30微米范围内，软骨细胞扁平，胶原纤维在这些细胞之间平行于表面方向排列。在关节软骨更深层，圆形细胞均匀分布于随机的胶原纤维网络中。在平台中心，切线层在生长过程中变化不大，而其下方的细胞层厚度增加，并在其组成的胶原和细胞成分组织中逐渐呈现出更垂直的特征。1周时，细胞被充满胶原纤维的无细胞区域分隔成簇。2周时，形成的放射状区域内的细胞排列成由垂直胶原纤维包围的柱状。在这个年龄段，这些垂直纤维与切线表面层的纤维的连续性很明显。软骨细胞被典型的软骨囊纤维包膜包围。到6周时，髁最中心的放射状胶原纤维基部以及相邻的肥大透明软骨已经钙化。直到骨骼成熟才出现坚实的软骨下板和潮线。从出生到6周龄，被确定为原始关节软骨的层的最大厚度从0.13毫米增加到0.70毫米，成年时为1.5毫米。然而，在整个生长过程中，平台中心切线层的厚度从未超过0.05微米。在髌骨、股骨头和胫骨平台周边，软骨发育遵循相同的一般顺序。与胫骨平台中心不同，切线层也增厚，但速度比放射状区域慢。在所有年龄段，发育中的关节软骨在结构上与更深层的透明软骨不同，后者通过软骨内成骨促进骨化中心的生长。关节软骨的胶原基质在出生后不久就获得了一种特征性的、有序的三维结构。软骨厚度的增加主要通过放射状区域的扩大来实现。
