Secondary Coronal Synostosis After Posterior Vault Distraction Osteogenesis.

Secondary synostosis of initially patent cranial sutures is a rare but recognized phenomenon following cranial surgery, particularly in syndromic cases. However, its incidence and risk factors in nonsyndromic patients remain unclear. This study aimed to investigate the occurrence and causes of secondary synostosis following surgical correction of lambdoid synostosis, with a focus on posterior vault distraction. Medical records of patients who underwent surgical treatment for unilateral or bilateral lambdoid synostosis between 2015 and 2024 at Keio University Hospital were retrospectively reviewed. Patients with syndromic craniosynostosis were excluded. Postoperative cranial computed tomography at 1 year was assessed for secondary synostosis. Surgical approaches included single-stage cranial remodeling and posterior distraction. Statistical analyses were performed using the Mann-Whitney U and Fisher exact tests, with logistic regression applied to identify significant risk factors. Thirteen patients underwent surgery: 7 with bilateral lambdoid and sagittal synostosis (BLSS) and 6 with unilambdoid synostosis. 9 patients underwent single-stage cranial remodeling, and 4 underwent posterior distraction. Secondary coronal synostosis developed in all 4 patients who underwent posterior distraction but in none of those who underwent single-stage remodeling. Logistic regression analysis identified posterior distraction as the strongest risk factor for secondary coronal synostosis, while BLSS was associated with secondary sagittal synostosis. One patient required reoperation due to elevated intracranial pressure. Posterior vault distraction in nonsyndromic lambdoid synostosis is associated with a high risk of secondary coronal synostosis. These findings highlight the importance of careful long-term monitoring and judicious surgical planning, particularly when distraction is considered.