The participation of cartilage canals in the ossification of the human fetal calcaneum.

The relationship of cartilage canals to the developing ossification centres in the human calcaneum was investigated. The cartilage canals were always present in the calcaneum by 78 mm CR length. The calcaneum has two primary ossification centres. The main centre was identified in the deep part of the calcaneum as a spherical zone of cartilage cells in the proliferative phase between 82 and 120 mm CR length and in the hypertrophic phase between 130-156 mm. Numerous cartilage canals entered the calcaneum from its dorsal and ventral surfaces and, between 106 and 156 mm CR length, they formed vascular arcades around this centre. Between 165 and 175 mm, calcification and marrow space formation were noted involving branches from the adjoining cartilage canals within these areas, which provided vascular osteogenic tissue to the early spaces. The inconstant parachondral centre, when present, may appear first during the fourth month as a periosteal reaction on the inferolateral side in the anterior wall of a deep groove in front of the posterior tuberosity of the calcaneum. By 120 mm CR length, a thin layer of subperiosteal bone was present along with a zone of early hypertrophic cartilage cells deep to it. Calcification and marrow space formation occurred by 165 mm and these marrow spaces were supplied by periosteal buds. Osteoid tissue was formed in them between 186 and 206 mm CR length. The main centre was oval in shape due to its posterolateral extension irrespective of the presence or absence of the parachondral centre.(ABSTRACT TRUNCATED AT 250 WORDS)