Histomorphological analysis of the effect of rigid fixation on growing sutures in the rabbit.

The effect of internal rigid fixation (IRF) on bone growth was studied in an experimental model set up in the rabbit. The frontonasal suture of the right side was surgically bridged by a microplate. As reference for bone growth, four screws were placed symmetrically in the four bony segments including the frontonasal suture on both sides. The suture development was followed dynamically for 40 days on the basis of the position of the screws established radiographically. The rate of bone formation along the sutural bones was evaluated by means of the tetracycline labelling technique. The structure of the newly formed bone and its degree of mineralization were respectively analysed under polarized light and with microradiography. It was demonstrated that IRF prevents growth of the sutural membrane but not of the osteogenic process; as a consequence the constrained sutures soon undergo synostosis. This fact must be taken into consideration when IRF is employed in children in order to avoid delayed removal of the plate irreversibly stopping the growth of the constrained suture.