The Journal of Bone and Joint Surgery, Vol 74, Issue 4 516-528, Copyright © 1992 by Journal of Bone and Joint Surgery, Inc
Cellular basis of decreased rate of longitudinal growth of bone in pseudoachondroplastic dogs
GJ Breur, CE Farnum, GA Padgett and NJ Wilsman
Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, Madison.
Regulation of growth of long bones occurs in cartilage growth plates, where
proliferation of chondrocytes, matrix synthesis, and an increase in
vertical height in the direction of growth all contribute to the final
length of a bone. In this study, we tested the hypothesis that an increase
in chondrocytic vertical height is a major variable that accounts for the
decreased rate of growth of long bones in Scottish deerhound dogs that had
pseudoachondroplasia. The diagnosis of pseudoachondroplasia is based,
primarily, on the demonstration of alternating electron-dense and
electron-lucent lamellae with a periodicity of 100 to 150 nanometers in
dilated rough endoplasmic reticulum. These ultrastructural changes are
similar to those seen in humans who have pseudoachondroplasia. In Scottish
deerhounds that have the disease, growth of bone is approximately 65 per
cent of that in normal animals. There were striking differences in the
diameters of proliferating and hypertrophic chondrocytes in
pseudoachondroplastic animals compared with normal animals. Specifically,
the horizontal diameter of proliferating chondrocytes was 22.7 micrometers
in normal animals and 11.3 micrometers in pseudoachondroplastic animals.
The vertical diameter of proliferating chondrocytes was 4.8 and 7.6
micrometers in normal and pseudoachondroplastic animals. In the distal 100
micrometers of the hypertrophic zone, the mean horizontal diameter of
hypertrophic chondrocytes was 29.6 and 19.1 micrometers and the mean
vertical diameter was 22.8 and 18.6 micrometers in normal and
pseudoachondroplastic animals. All these differences were statistically
significant. The changes in vertical height resulted in a significant
difference in the incremental difference in vertical height between
chondrocytes from the proliferative and hypertrophic zones in normal
animals (18.0 micrometers per chondrocyte) and pseudoachondroplastic
animals (11.0 micrometers per chondrocyte). Each chondrocyte in the
abnormal plates achieved only 61 per cent of the incremental difference of
chondrocytes in normal plates. The mean cellular volume of chondrocytes in
the hypertrophic zone was 13,050 cubic micrometers in the normal animals
and 10,740 cubic micrometers in the pseudoachondroplastic animals. This
difference was not statistically significant. These results are discussed
in relation to current theories of the role of the shape and change in
volume of chondrocytes in the regulation of longitudinal growth of
bone.(ABSTRACT TRUNCATED AT 400 WORDS)
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