Sagittal craniosynostosis is the most common non-syndromic isolated craniosynostosis (Kolar, 2011). It characteristically presents biparietal narrowing and variable degrees of frontal bossing and occipital prominence, resulting in a scaphocephalic head shape. Surgical approaches for correcting these cranial vault changes cover a spectrum ranging from linear craniectomy of involved suture (open or endoscopic), with or without helmet therapy, spring cranioplasty, through to extensive craniectomies, with varying approaches to remodelling and reconstruction (Epstein et al., 1982; Jimenez et al., 2004; Mackenzie et al., 2009). Most techniques aim to release the constraining force of the fused suture on brain growth, creating a bony defect with exposed dura that remains patent long enough for the growing brain to reshape and normalise the cranial vault contour. This immediately leaves a sizeable cranial defect in the early phase after the operation (Fig. 1).

To date, little information about the subsequent behaviour of these craniectomy defects, especially the pattern and speed of new bone formation in infants with craniosynostosis, has been discovered. An older technique amounting to subtotal calvariectomy (Powiertowski and Matlosz, 1965) developed in the infancy of craniofacial surgical procedures was associated with poor or unpredictable bone regrowth outcomes. Recent reports identify a range of extensive cranial vault remodelling (CVR) procedures - either leaving large areas of exposed dura (Moore et al., 2021) or more detailed and prescribed reconstruction (Greensmith et al., 2008), which appear to correct the scaphocephalic head shape with a low rate of recurrence.

Since inception, the imaging protocol for craniosynostosis in our unit has routinely included preoperative and one-week postoperative CT scans where infant cranial vault surgery occurred to review early outcomes and identify any missed intracranial complications. A recent change to align imaging with a routine clinical review 6–8 weeks after surgery additionally provided the opportunity to explore and better understand the pattern and progress of bone reformation after CVR. Also, this adds benefit in patients’ caregivers' acknowledgement regarding their concerns of the significant cranial defects after CVR.

Investigating the temporal and spatial response of bone reformation during the weeks and months after CVR should aid understanding and improved prediction of short- and long-term outcomes. This includes the timing of surgery, the intra-operative determinants influencing bone regrowth and the extent and need for definitive reconstruction or not. Thus, this study aimed to investigate the postoperative bone reformation percentage, rates and re-osteogenesis patterns in isolated non-syndromic sagittal craniosynostosis patients.