The Journal of Bone and Joint Surgery, Vol 68, Issue 2 243-255, Copyright © 1986 by Journal of Bone and Joint Surgery, Inc
Morphometric analysis of chondrocyte hypertrophy
JA Buckwalter, D Mower, R Ungar, J Schaeffer and B Ginsberg
In the hypertrophic zone of the cartilaginous growth plate, chondrocytes
enlarge, assume a more spherical shape, and form a population of cells
called the hypertrophic chondrocytes. The mechanisms that are involved in
the formation of hypertrophic chondrocytes are poorly understood. Cell
hypertrophy usually refers to an increase in cell size and volume
associated with an increase in organelles. In this study, we sought to
determine whether the formation of hypertrophic chondrocytes represents
true cell hypertrophy associated with an increase in organelles or whether
it is due to swelling and fluid accumulation. Morphometric analyses of
electron micrographs were carried out to determine changes in cell number,
cell volume, cell organelle volumes, and matrix volumes in the reserve
zone, upper proliferative zone, lower proliferative zone, upper
hypertrophic zone, and lower hypertrophic zone. Between the upper
proliferative zone and the lower hypertrophic zone, the cells increased
their mean volume more than 500 per cent. As they enlarged, their matrices
altered; territorial matrix volume increased as its collagen content
decreased, and interterritorial matrix volume decreased as its collagen
content increased between the lower proliferative zone and the lower
hypertrophic zone. Between the upper proliferative zone and the lower
hypertrophic zone, the absolute volume per cell of endoplasmic reticulum,
Golgi membranes, and mitochondria increased 126 per cent, while the volume
of cytoplasm and nucleoplasm increased 779 per cent, apparently by
accumulation of water. Cell organelles of the lower hypertrophic zone did
not show the changes that are associated with cell injury or death. Thus,
the synthesis of organelles contributed to chondrocyte enlargement, but the
primary mechanism of cell enlargement was cytoplasmic and nuclear swelling.
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