The Journal of Bone and Joint Surgery, Vol 69, Issue 2 174-184, Copyright © 1987 by Journal of Bone and Joint Surgery, Inc
Metatropic dwarfism. Uncoupling of endochondral and perichondral growth
SD Boden, FS Kaplan, MD Fallon, R Ruddy, J Belik, E Anday, E Zackai and J Ellis
Metatropic dwarfism is a rare heritable skeletal dysplasia that is thought
to result from a defect in endochondral ossification. Histological studies
have been few and have yielded inconsistent findings. In addition, no
investigator has commented on the structure and function of the
perichondral portion of the growth plate in patients who have metatropic
dysplasia. To further characterize this disturbance, histological studies
were carried out on autopsy specimens from the proximal part of the femur
and the iliac crest of a patient who had this disorder. The major findings
were: the absence of formation of normal primary spongiosa in the
metaphysis; the presence of a thin seal of bone at the chondro-osseous
junction, with abnormal metaphyseal vascular invasion and arrest of
endochondral growth; and normal-appearing perichondral ring structures with
persistence of circumferential growth. These findings suggest an uncoupling
of endochondral and perichondral growth and offer an explanation for the
dumbbell-shaped morphological structure of the osseous metaphysis that is
seen in patients who have metatropic dysplasia. Other observations included
prominence of the cartilaginous canals and vascular channels in the reserve
zone; clumping of chondrocytes with enhanced staining of the pericellular
matrix in the proliferative zone; a decreased ratio of cells to matrix in
the hypertrophic zone, with intracellular metachromatic granules and
incomplete evolution of chondrocytes; complete absence of an
alcian-blue-positive zone of provisional calcification; and, finally,
islands of dysplastic chondrocytes in the metaphysis. These abnormalities
suggest that metatropic dysplasia is not simply a disorder of endochondral
ossification. There appear to be associated defects in the longitudinal
proliferation and maturation of chondrocytes and in the production of
normal matrix.
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