There is some uncertainty as to when normal fusion of the metopic suture occurs. Existing studies have included relatively small numbers and have not used a statistical model to represent any variation in normality. In this study, a total of 337 head computed tomographic scans performed between 2006 and 2009 were retrospectively reviewed after strict exclusion criteria were met. Only patients aged younger than 18 months were included. Assessment was performed by analyzing axial slices of the bony window of the computed tomographic scan by 2 independent investigators. Two separate probit analyses were carried out to estimate the proportion of patients in whom the fusion process would have started and completed. Of 337 patients, 204 (60.5%) were male and 133 were female (39.5%). All patients older than 15 months and 23 days had completely fused metopic sutures. The estimated median age for the start of the fusion process was 4.96 months (95% confidence interval, 3.54–6.76 months), and the estimated median age for the completion of fusion was 8.24 months (95% confidence interval, 7.37–9.22 months). The fusion process completed between 2.05 and 14.43 months of age in 95% of the normal population. The difference between sexes was not significant. In conclusion, there was wide variation in the timing of normal fusion that can complete as early as 2 months of age.
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