Effects of repetitive strains on vertebral end plates in young rats.

A histologic study of vertebral end plates was performed on young rats' tails subjected to intensive passive motion. Seven six-week-old rats had two-hour motion cycles daily, for two months. Histologic changes of proximal caudal vertebrae in the experimental group were compared with those of a control group of seven rats of the same litter which were allowed to grow freely without mechanical stress. The main findings were three striking protrusions of disk tissue into end plates, not observed in the control animals. End plate axial bulges lacking spindle-shaped cells and an increase in chondrocytes in the adjacent articular cartilage were observed. The growth-plate thickness was uneven and was absent in some areas, with disorganization of chondrocyte columns. All of these findings were present to a lesser degree in the control group and appeared to be similar to histologic changes observed in Scheuermann's disease.