Orthopaedic Clinic, University of Brescia, Brescia, Italy.
J Anat. 2012 Apr;220(4):372-83. doi: 10.1111/j.1469-7580.2012.01477.x. Epub 2012 Feb 13.
The kinetics of osteogenic cells within secondary osteons have been examined within a 2-D model. The linear osteoblast density of the osteons and the osteocyte lacunae density were compared with other endosteal lamellar systems of different geometries. The cell density was significantly greater in the endosteal appositional zone and was always flatter than the central osteonal canals. Fully structured osteons compared with early structuring (cutting cones) did not show any significant differences in density. The osteoblast density may remain constant because some of them leave the row and become embedded within matrix. The overall shape of the Haversian system represented a geometrical restraint and it was thought to be related to osteoblast-osteocyte transformation. To test this hypothesis of an early differentiation and recruitment of the osteoblast pool which completes the lamellar structure of the osteon, the number and density of osteoblasts and osteocyte lacunae were evaluated. In the central canal area, the mean osteoblast linear density and the osteocyte lacunae planar density were not significantly different among sub-classes (with the exclusion of the osteocyte lacunae of the 300-1000 μm(2) sub-class). The mean number of osteoblasts compared with osteocyte lacunae resulted in significantly higher numbers in the two sub-classes, no significant difference was seen in the two middle sub-classes with the larger canals, and there were significantly lower levels in the smallest central canal sub-class. The TUNEL technique was used to identify the morphological features of apoptosis within osteoblasts. It was found that apoptosis occurred during the late phase of osteon formation but not in osteocytes. This suggests a regulatory role of apoptosis in balancing the osteoblast-osteocyte equilibrium within secondary osteon development. The position of the osteocytic lacunae did not correlate with the lamellar pattern and the lacunae density in osteonal radial sectors was not significantly different. These findings support the hypothesis of an early differentiation of the osteoblast pool and the independence of the fibrillar lamellation from osteoblast-osteocyte transformation.
已在二维模型中检查了次级骨单位内成骨细胞的动力学。比较了骨单位的线性成骨细胞密度和骨陷窝密度与其他不同几何形状的骨内膜层板系统。在骨内膜附著区的细胞密度显著更高，且始终比中央骨单位管腔更平坦。与早期结构（切割锥）相比，完全结构的骨单位在密度上没有任何显著差异。成骨细胞密度可能保持不变，因为其中一些细胞离开行列并嵌入基质中。哈弗斯系统的整体形状代表了一种几何限制，并且被认为与成骨细胞-骨细胞转化有关。为了验证这种关于成骨细胞池的早期分化和募集完成骨单位层板结构的假设，评估了成骨细胞和骨陷窝的数量和密度。在中央管区域，亚类之间（排除 300-1000μm(2) 亚类的骨陷窝）的平均成骨细胞线性密度和骨陷窝平面密度没有显著差异。与骨陷窝相比，成骨细胞的平均数量在两个亚类中明显更高，在两个中间亚类（具有较大管腔）中没有明显差异，在最小的中央管亚类中明显更低。TUNEL 技术用于鉴定成骨细胞内细胞凋亡的形态特征。发现细胞凋亡发生在骨单位形成的晚期，但不在骨细胞中。这表明细胞凋亡在平衡次级骨单位发育过程中成骨细胞-骨细胞平衡中具有调节作用。骨陷窝的位置与层板模式无关，骨单位的径向扇区的骨陷窝密度没有显著差异。这些发现支持成骨细胞池的早期分化以及纤维层板与成骨细胞-骨细胞转化无关的假设。
