INTERNAL CALVARIAL BONE DISTRACTION IN RABBITS WITH DELAYED-ONSET CORONAL SUTURE SYNOSTOSIS

Recent studies have identified a subpopulation of craniosynostotic ind ividuals who exhibit progressive or delayed-onset synostosis and mild craniofacial growth abnormalities. These individuals may be good candi dates for nonextirpation, distraction osteogenesis therapy. The presen t study was designed to test this hypothesis by using internal calvari al bone distraction in a rabbit model with familial delayed-onset cran iosynostosis. Data were collected from 159 rabbits:71 normal controls, 72 with delayed-onset coronal suture synostosis, 8 with delayed-onset coronal suture synostosis and coronal suturectomy, and 8 with delayed -onset coronal suture synostosis and distraction. At 10 days of age, a ll rabbits had amalgam markers placed on both sides of the frontonasal , coronal, and anterior lambdoidal sutures. At 25 days of age, correct ion was accomplished through either a 5-mm-wide suturectomy or distrac tion osteogenesis. An internal distraction appliance was fixed to the frontal and parietal bones and percutaneously and intermittently activ ated at an average of 0.10 mm/day for 42 days (4.11 mm total). Serial radiographs were taken at 10, 25, 42, and 84 days of age. Results reve aled that rabbits with delayed-onset synostosis had significantly (p < 0.01) reduced coronal suture growth rates (0.04 mm/day) compared with the other three groups (0.07 mm/day). Rabbits with suturectomy and ra bbits with distraction showed similar coronal suture responses. Howeve r, from 42 to 84 days of age, rabbits with distraction showed reduced growth at the vault sutures and abnormal growth patterns in cranial va ult width, cranial vault shape, and cranial base angulation compared w ith the other three groups. Results demonstrated that, although the no rmal coronal suture growth rate was maintained in rabbits with delayed -onset synostosis using intermittent distraction osteogenesis, normal adult craniofacial structure was not achieved. Such anomalous growth w as probably a result of altered growth Vectors and compressive forces at adjacent sutures during distraction. These findings suggest that di straction osteogenesis without corticotomy may be a treatment alternat ive in individuals with progressive, delayed-onset synostosis,but that internal appliances that generate low-level, continuous distractive f orces should be investigated and developed.