Posterior Vault Distraction Osteogenesis: Rates of Ossification in Bone Gaps After Consolidation

The authors observe significant bone gaps upon distractor removal in posterior vault distraction osteogenesis (PVDO). The purpose of this study was to quantify bone gaps upon distractor removal, determine whether they close over time, determine if they predispose to relapse, and investigate whether age affects rate and degree of re-ossification. The authors performed a retrospective review of PVDO patients and included those with computed tomography (CT) scans at 2 timepoints: 1 at completion of consolidation and another at least 4 months later. Using Mimics software, bone gaps were traced to calculate total surface area. A paired t test and linear regression were used to compare size of bone gaps, presence of relapse, and rates of re-ossification. Sixty-nine patients were identified, with 7 meeting inclusion criteria. Three were under 1 year. Consolidation began 28.3 ± 6.0 days after surgery and continued for 64.9 ± 14.5 days. Length of time between CT scans was 7.5 ± 2.7 months. A significant decrease in bone gaps occurred between scans (33.4 ± 14.6 cm2 versus 19.2 ± 17.2 cm2, P = 0.005). After consolidation, ossification occurred at a rate of 2.4 cm2/month (P = 0.046). The rate of bony regeneration in patients under and over 1 year was 4.3 cm3/month (P = 0.025) and 1.5 cm3/month (P = 0.552), respectively. Despite differential bony regeneration rates, no patient demonstrated relapse. From this study, the authors conclude the following. Calvarial bone gaps are present after PVDO consolidation. These gaps undergo re-ossification at a rate that appears to be faster in infants. Overall, they decrease in size over time. The presence of bone gaps does not correlate with relapse of cranial expansion.