Internal calvarial bone distraction in rabbits with experimental coronal suture immobilization : effects of overdistraction

This study was designed to assess the effects of over-distraction of an experimentally immobilized coronal suture using an internal appliance on craniofacial growth in rabbits. Fifty-three, 1.5-week-old rabbits were used. Markers were placed on either side of the calvarial sutures. Thirty-nine rabbits had bilateral coronal suture immobilization using methyl methacrylate ; 14 rabbits served as normal controls. At 6 weeks of age, the 39 immobilized rabbits were randomly assigned to four groups : (1) immobilized controls (n = 14) ; (2) suturectomy (n = 6) ; (3) suturectomy with distraction (n = 9) ; and (4) suturectomy with overdistraction (n = 10). Lateral head radiographs were taken at 1.5, 6, 12, and 18 weeks of age. Results revealed that, by 18 weeks of age, rabbits with overdistraction exhibited significant compensatory growth abnormalities in the cranial vault, midface, and anterior cranial base compared with the other groups. Results indicate that overdistraction may contribute to craniofacial anomalies through altered growth vectors and compressive tension-stress forces at adjacent sutures and suggest that it may be important to keep pace with the growing coronal suture and neurocapsular matrix during distraction to reestablish normal craniofacial morphology.