A morphological study of the development of the tibial proximal epiphysis and growth plate of normal and dwarfed Snell mice.

In normal and dwarfed Snell mice, the postnatal development through the first 70 days of life of the proximal tibial epiphysis and its growth plate has been studied, using histometric techniques and qualitative histological descriptions. The tibia appears to be fairly representative for longitudinal skeletal growth, since a linear relationship between partial tibia length (PTL) and body length was found. In dwarf mice PTL is deviating from normal at approximately 14 days of age. Histological difference becomes apparent much earlier. At five days of age in normal mice, hypertrophic cartilage cells appear, foreshadowing the development of the secondary centre of ossification. In dwarf mice this centre develops after 9 days of age, its size remains far below normal. Furthermore ther is a great difference in the thickness of various cartilage zones with age: the R-zone remains quite large in dwarfs, in contrast to normals; the P-zone changes almost completely in parallel in normals and dwarfs and the D-zone in dwarfs is narrower from the beginning. In addition there is a collapsed and disorganized aspect of the rows in the P-zone in dwarfs. Therefore it can be concluded that the hormonal deficiencies in dwarfs lead to more profound disturbances than just a retarded but otherwise normal growth and development. The specific role of each hormone in the processes will be better understood by detailed replacement studies.