Perinatal development of the rat hip joint with restrained fetal movement.

We compared the structures of the femoral head (FH) of neonates between normal and operated legs with restrained fetal movement using an exo utero technique. At embryonic day (E) 16.5, one hind limb was sutured onto the embryonic membrane and the fetuses were allowed to develop exo utero until the term (E22.5). There was no significant difference in the largest diameter of the FH between the non-operated and operated side FH in the operated neonates and the FH of the non-operated neonates. By scanning electron microscopy, roughness and collagen fiber bundles, which were detected on the surface of the operated side FH at E18.5, disappeared at E22.5. However, the operated side FH was deformed and the surface cell arrangement was more irregular than that of the controls at E22.5 by light microscopy. These results suggest that the abnormality of cell arrangement caused by the restraint of fetal movement may induce the deformity and irregularity of the FH surface, although this operation may not disturb the basic cellular activities such as cell proliferation as well as the secretion of cartilage ma-trix and collagen fibers. To further investigate the recovery process in the operated newborns after releasing the restraint, we bred them artificially for a considerable period after birth. The operated side FH surface of the neonate bred for 45 hours was smoother than that at E22.5 and similar to that of the non-operated side FH. This result suggests that the proper movement of the extremities after birth may recover the deformity caused by restrained fetal joint movement.