Ultrastructural Studies of Initial Stages of Mineralization of Long Bones and Vertebrae in Human Fetuses

Abstract

We studied 27 embryos of 5–12 weeks gestational age where pregnancy was interrupted due to paramedical reasons, in order to find the developmental stages at which matrix vesicles appear in cartilage, and whether they are involved in the mineralization process. Specimens of long bones, lumbar and thoracic vertebral column were prepared for light, transmission and scanning electron microscopic studies. In the cartilaginous models of long bones, matrix vesicles were found amongst maturing and hypertrophic chondrocytes already by the 6th week after fertilization. By that stage, bone rudiments consisted of only cartilage that was not yet mineralized. In the vertebral column matrix, vesicles were found in the vertebral bodies amongst maturing and hypertrophic chondrocytes at the beginning of the 8th week. At that stage, although hypertrophy of chondrocytes was observed, mineralization was still absent. No matrix vesicles were found in the perichondrium, investing mesenchyme and intervertebral discs. Mineralization of cartilage in long bone rudiments started in the form of hydroxyapatite crystals within or around the matrix vesicles at 7 weeks of age and in the vertebral column at 11 weeks. As mineralization progressed, more hydroxyapatite crystals were observed around the matrix vesicles, forming typical calcospherites. Mineralization then progressed in the form described in other animals.

Multifocal Synovial Calcinosis as Manifestation of a Calcified Aponeurotic Fibroma

“…Der Mechanismus der Verkalkung, die von granulären Kalkablagerungen [11 (a)] bis zu den in dieser Kasuistik beschriebenen Kalkschollen reicht, bleibt offen. Ultrastrukturell liegen weder die Zeichen der dystrophen Verkalkung mit Auftreten von Kalkosphäriten vor, wie sie in arteriosklerotischen Beeten gesehen wird [12], noch die globulär angeordneten Kalksalze, wie sie die provisorische Verkalkung bei der endochondralen Ossifikation kennzeichnen [3]. Transmissionselektronenmikroskopisch fanden sich Kristallnadeln, die am ehesten an Apatitkristalle erinnern, wie sie in Knochenfragmenten bei der Detritussynovialitis auszumachen sind [11 (b)].…”