INTRODUCTION: Posterior vault distraction is often performed for correction of brachycephaly associated with craniosynostosis. Secondary fusion of initially patent cranial suture is seldom observed after surgical correction, and its incidence is reported to be between 10% and 37%. But its incidence, mechanism, and influence on cranial growth are not well described specifically after posterior vault distraction. Especially, the influence of compression to the patent suture during distraction on secondary synostosis is yet to be elucidated. This retrospective study was conducted to investigate these questions.
METHODS: To elucidate the influence of compression effect during distraction on secondary synostosis, patients with lambdoid synostosis were selected, in whom patent coronal suture lies perpendicular to the direction of force exerted by the posterior distraction. Retrospective chart review was performed on 5 patients with bilateral lambdoid and sagittal synostosis and 1 patient with bilateral lambdoid synostosis who underwent posterior vault distraction between 2002 and 2018 at National Center for Child Health and Development, Tokyo, Japan. CT images were used to determine the patency of cranial sutures, and head circumference was used to evaluate cranial growth.
RESULTS: Posterior vault distraction was performed at median age of 12 months (range, 6–15). On CT images, the coronal suture was patent before operation, but it was partially or totally fused at median of 5 months (range, 1–7) after operation in all the patients. At the latest follow-up at median of 36 months (range, 13–131), synostosis of the coronal suture progressed to total and remained fused in all the patients. The median head circumference was 62 percentile (range, 44–90) before operation. It increased to approximately 100 percentile at median of 9 months (range, 8–14) after operation except for 1 patient whose data were not available, and it continued to increase along the growth curve afterward.
DISCUSSIONS: The initially patent coronal suture was fused in all of the 6 patients with lambdoid synostosis after posterior cranial vault distraction. Several possible explanations exist for this phenomenon, including decompression of intracranial pressure after cranial expansion and surgical invasion on cranial bone. But high incidence in the present study compared with the past literature suggests that the compression on the coronal suture during distraction may play important role in the secondary synostosis. The impact of secondary synostosis on cranial growth seems minimal, considering the fact that the normal rate of head growth was observed even after the coronal suture remained fused. The patients in this study were thought to have obtained sufficient cranial volume by distraction and reached the gradual phase of cranial growth which is not dependent on the patent suture. Higher risk of secondary synostosis is expected when performing posterior vault distraction, especially when the compression force is exerted on the patent suture during distraction. It is important to obtain sufficient cranial volume by distraction so that cranial volume is maintained with gradual cranial growth even after secondary synostosis. Further study is warranted to elucidate the incidence, mechanism, and impact of secondary synostosis after cranial vault distraction.