The development of centres of ossification of bones forming elbow joints in young swine
Visco, D.M.; Hill, M.A.; Van Sickle, D.C.; Kincaid, S.A.
Journal of Anatomy 171: 25-39
1990
ISSN/ISBN: 0021-8782 PMID: 2081708 Document Number: 361539
The mammalial skeleton develops by a process of intramembranous and endochondral ossification. Diaphyseal and epiphyseal centres of ossification of long bones develop within the cartilaginous anlage as a result of the latter process. However, the initiation, formation and expansion of epiphyseal centres of ossification and the roles that cartilage canals may play in these processess are poorly understood. Because of the conflicting information about their development, the objective of the present study was to examine the epiphyseal centres of ossification involved in the formation of the humero-radio-ulnar joints of pigs between 1 day and 15 weeks of age. Cartilage and bone were examined radiographically, macroscopically, mesoscopically and microscopically. Thoracic limbs from 39 pigs were perfused with India ink or silicone rubber injection compound and the bones were dissected free of soft tissues. The humerus, ulna, and radius were fixed in formalin or ethyl alcohol and then cleared by the modified Spalteholz technique. Bones were radiographed, examined grossly, and then cut into slabs for mesoscopical evaluation. Foci considered to be calcifying within cartilaginous anlages were selected for microscopical examination. The epiphyseal centres of ossification developed at different times in different sites and enlarged by a series of steps. Microscopical evidence of initiation of ossification was a cluster of hypertrophied chondrocytes adjacent to one side of a cartilage canal. Next, interterritorial matrix became calcified between the hypertrophied chondrocytes at a distance equivalent to two or three times the diameter of a chondrocytes away from the cartilage canal. As the focus enlarged, additional matrix calcified and the cartilage canal appeared to be encompassed by the focus of calcification. With further enlargement of the focus, the entire cartilage canal was surrounded by an area of endochondral ossification and subsequently was at the centre of the focus. A group of enlarging foci eventually coalesced to form a single centre of ossification. Mesoscopical examination was more useful than radiographical examination for identifying small foci of calcification which preceded epiphyseal centres of ossification.