CHONDROCYTE MATURATION CYCLE AND ENDOCHONDRAL OSSIFICATION IN HUMAN FETAL CARTILAGE

The initial calcification and the progression of the mineral phase
depositing in cartilage and bone matrix was studied in human,
fetal cartilage Anlagen at a developmental stage when the calcified
cartilage resorption had not yet started. The model
allowed a morphological, comparative analysis of the calcification
process in both cartilage and osteoid which represented the
basic steps of endochondral calcification. The study was carried
out with light microscopy and SEM-Edax (combined with hest
deproteination and morphometry) on a sequence of thin sections,
cut on the same paraffin inclusions. This allowed to analyzed
corresponding fields with the different microscopy techniques.
In cartilage focal, globular mineral deposits (randomly
distributed) represented the initial phase of calcification which
progressed with an eccentrical growth of the single deposit. With
the increase of calcified globules size and of their density, aggregation
led to the extensive mineralization of the inter-territorial
matrix. Mineral deposition in osteoid below the periosteal
osteoblasts occurred shortly after the collagen fibrils at thin
extruded from the osteoblast cell membrane and packed in compact
bundles. The fibrils themselves acted to orient and to compact
the mineral deposits along a direction of the fibrils. This
study documented the progression of the mineral deposition in
both cartilage and osteoid and integrated the actual knowledge
of the initial Calcium Phosphate nucleation in endochondral
ossification.