Background: The growth plate increases its activity in response to exercise
. Likewise, decreased physical activity exerts a negative effect on bone gr
owth and development, leading to rarefaction of the subepiphyseal bone. Lim
b immobilization inhibits the growth plate's activity, indirectly shown by
a recorded arrest in longitudinal growth of the long bones. However, there
is no direct evidence concerning the growth plate itself.
Objective: To determine whether the growth plate exhibits measurable micros
tructural changes in response. to decreased levels of physical activity.
Methods: Histomorphometric analysis was used to qualitatively and quantitat
ively assess the changes in the epiphyseal plate in response to single hind
limb immobilization in the rat. In 16 of 25 Sprague-Dawley male rats the l
eft hind limb was immobilized for 3 weeks; the remaining 9 rats served as c
ontrols, The left proximal tibia of each animal was examined by computerize
d image analysis.
Results: There was a decrease in epiphyseal height, cell column density and
subepiphyseal trabecular area all indices of growth plate activity. Metaph
yseal cortical thickness was also depressed, thereby confirming the efficac
y of the immobilization method applied,
Conclusions: Limb immobilization in the rat induces inhibitory histological
changes in the epiphyseal growth plate, which are in contrast to the excit
atory microscopic changes seen with exercise. These changes can be assessed
quantitatively, Their potential for reversibility remains to be determined
by future experiments.