The aim was to assess the stability of monobloc distraction osteogenesis using three-dimensional computed tomographic (CT) scan volume-rendered images with the "biporion-dorsum sellae" plane. This was a prospective study of patients undergoing monobloc internal distraction osteogenesis at the International Craniofacial Institute, Dallas, TX. Measurements were made of the perpendicular distance of 8 skeletal facial points to the static "biporion-dorsum sellae" plane. The statistical analyses were performed with the paired-samples t test in SPSS. Three male patients were included in the study. Of these patients, 2 had Apert syndrome (A, B) and 1 had Carpenter syndrome (C). The mean age was 73 (range 30-112) months, and the mean follow up was 14 (range 8-12) months. The consolidation period was 17, 23, and 28 weeks in each patient, respectively. In patient A, the paired-samples t test of matched points was P = 0.022. Further analysis of the three-dimensional lateral profile revealed an obvious relapse, and predistractor removal CT scans (at 17 weeks) also showed deficient bone growth across the distraction gaps at the anterior cranial fossae and the temporal bones. In contrast, patients B and C showed a stable outcome after distraction and after removal of distraction devices. On analysis of the predistractor removal three-dimensional CT scans (23 and 28 weeks, respectively), there was more bone growth across the distraction gaps at the anterior cranial fossa and temporal bones. The "biporion-dorsum sellae" plane was used to assess the results of monobloc distraction osteogenesis. Relapse was associated with inadequate bone growth across the anterior cranial fossa and temporal bone. The findings seem to point the way for an increased consolidation period and more detailed examination of the CT scans before removal of internal distraction devices.
