Ultrastructural investigation of calcification and ossification in experimental fracture healing with special reference to osteogenic role of fibroblasts.
OBJECTIVE
To investigate ultrastructurally the process of calcification and ossification in experimental fracture healing.


METHODS
A standardized fracture of the radius was made in rabbits. Undecalcified callus tissues from different fracture regions were subjected to ultrastructural observation under transmission electron microscope.


RESULTS
In the mitochondria and membrane-bound vesicles of the fibroblasts, osteoblasts and chondrocytes, high electron density calcium granules were seen. These granules provided raw materials for the deposition of calcium salt crystals. Around these cells, round, oval or irregularly shaped matrix vesicles could also be discerned, and they became calcified and formed flocculent calcospherules. Then in the Type I collagen fibrils around the fibroblasts and osteoblasts, and in the Type II collagen fibrils around the chondrocytes, calcium salt crystals also appeared. Innumerable flocculent calcospherules and calcified collagen fibrils coalesced together, expanded and finally turned into pieces of bone tissues. The fibroblasts also possessed the indispensable prerequisites for calcification and ossification in fracture healing. They either transformed into osteocytes or degenerated, perished and eventually were replaced by bone tissues.


CONCLUSIONS
Sequence of events taking place in calcification and ossification in experimental fracture healing was depicted. Calcification of matrix vesicles and collagen fibrils triggered these processes. Evidence of osteogenic role played by fibroblasts was provided.
Chai
B
B
Shanghai Institute of Traumatology and Orthopaedics, China.
Tang
X
X
Li
H
H
D000818:Animals; D002113:Calcification, Physiologic; D005347:Fibroblasts / Q000502:physiology / Q000648:ultrastructure; D017102:Fracture Healing / Q000502:physiology*; D008297:Male; D008854:Microscopy, Electron; D010012:Osteogenesis; D011817:Rabbits; D011885:Radius Fractures / Q000473:pathology / Q000503:physiopathology*