实验性骨折愈合中钙化与骨化的超微结构观察（兼论成纤维细胞的成骨作用）

Ultrastructural Investigation of Calcification and Ossification in Experimental Fracture Healing(With Special Reference to Osteogenic Role Played by Fibroblasts)

应用透射电镜对家兔桡骨标准骨折愈合过程中的钙化与骨化进行超微结构观察。发现在成纤维细胞、成骨细胞及软骨细胞的线粒体内，或具膜结构的空泡内，有深电子密度的钙颗粒。钙颗粒抵达细胞对钙化的部位，为钙盐结晶提供原料。在三种细胞的四周出现圆形、卵圆形或不规则形态的基质小泡。基质小泡内及其表面出现细针状的深电子密度钙盐结晶，结晶不断增加，形成丛毛球状钙球。然后，在成纤维细胞及成骨细胞四周的Ⅰ型胶原纤维内，以及软骨细胞四周的Ⅱ型胶原纤丝内，都出现钙盐结晶。无数丛毛球状钙球及钙化胶原纤丝不断接触、融合、扩大而形成一片骨组织。成纤维细胞，象成骨细胞及软骨细胞一样，在骨折愈合中也具备钙化与骨化所必需的条件，从而参与成骨。成纤维细胞最终演变为骨细胞，或变性、死亡而为骨组织所替代。

The processes of calcification and ossification in healing of a standardized fracture were studied ultrastructurally with transmission electron microscope.A 3 mm defect was produced in rabbit radius just distal to the insertion of pronator teres muscle.Two to three animals each were sacrificed on 3rd,5th,9th,13th,17th,21st and 25th postfracture days.Callus tissues from 5 different fracture regions,i.e.periosteal,bridging,uniting and proximal and distal sealing callus tissues,were procured and processed into ultrathin sections under undecalcified conditions and then subject to transmission electron microscopic study.In the mitochondriae or membrane bound vesicles of the fibroblasts,osteoblasts and chondrocytes emerged electron dense calcium granules.These calcium granules,after reaching the extracellular calcifying milieu,provided raw materials for the deposition of calcium salt crystals.In the pericellular surroundings of the fibroblasts,osteoblasts and chondrocytes could be seen round,oval or irregular shaped matrix vesicles,invested with and limited by tri laminar membrane.In the substance and on the surface of these matrix vesicles could be discerned fine needle shaped calcium salt crystals with deep eletron density.The crystals increased in amount and formed flocculent calcospherules.Thereafter,the calcium salt crystals were also deposited in the Type Ⅰ collagen fibrils around the fibroblasts and the osteoblasts,and in the Type Ⅱ collagen fibrils around the chondrocytes.These calcium salt crystals rendered the two types of collagen fibrils electron dense.Innumerable flocculent calcospherules and calcified collagen fibrils came into intimate contact,fused together,expanded and formed a piece of bone tissues.The fibroblasts,just like the osteoblasts and chondrocytes,possessed the prerequisites indispensable to calcification and ossification in the course of fracture healing and thereby took active part in osteogenesis.The fibroblasts turned eventually into osteocytes,or underwent degenerative changes leading to their death and replacement by bone tissues.(Original article on page 4)