Effects of Restrained Fetal Movement on the Development of the Rat Hip Joint

Abstract

ABSTRACTThe effect of fetal movement on the development of the hip joint was examined by restraining the leg movement using exo utero operation in rat fetuses. At embryonic day (E) 16.5, when the hip joint cavity starts to form, one side of the hind limb was sutured onto the embryonic membrane. After exo utero development to E18.5, the hip joint of the operated side was compared morphologically with those of the unoperated side, sham‐operated and unoperated in utero controls. The largest diameter of the femoral head (FH) and the gross morphology of the joint cavity of the operated side was not different from those of controls. By light microscopy (LM), the surface of the control E18.5 FH and acetabulum was smooth and covered by thin scale‐shaped cells which were partially pyknotic, and oval‐shaped cells underneath were rather regularly arranged in a thickness of a few cells. By transmission electron microscopy (TEM), scale‐shaped cells covered the FH surface incompletely, and the spaces in‐between were filled with the intercellular matrix. Oval‐shaped cells underneath had well developed rough endoplasmic reticulums. By scanning electron microscopy (SEM), mounds and grooves on the FH surface were evident at E17.0 but became unclear at E18.5. Subsurface collagen fibers formed a coarse meshwork at E17.0 but formed bundles at E18.5. On the operated side, by LM, the surface of the FH and acetabulum was irregular and lined by spindle‐shaped cells, whereas the underlying mesenchymal cells also showed an irregular cell shape and arrangement. By TEM, collagen fibrils in intercellular spaces were dense but did not generally form bundles. By SEM, the FH surface was rugged with banks and subsurface collagen fibers did not form bundles but remained as a dense meshwork. These results suggest that the fetal hind limb movement influences development of the surface structure of the FH and acetabulum and that this system may be useful to study prenatal etiology of the congenital dislocation of the hip.