Evolution of pelvic incidence and lumbar lordosis during growth: MRI-based evaluation from fetal stage to early childhood.

Purpose: Upstanding posture depends on the balance between the pelvis and spine, with minimal energy expenditure when spinal segments are aligned. Pelvic incidence (PI), a key measure of sagittal balance, is a constant individual characteristic that correlates with lumbar lordosis (LL) in adults. While sagittal balance has been widely studied in adults, there is limited research on the pediatric population, particularly pre-walking children and fetuses.

Methods: This study aimed to describe the development of PI and LL in healthy fetuses and children under 10 years old using MRI measurements. A retrospective analysis of MRI images from 96 subjects (20 fetuses and 76 children) undergoing MRI for non-spinal conditions was conducted. PI, wedging lumbar vertebral body angles (WVB) of L1-L5, and the sum of all WVB angles (SLL) were measured to assess their development and correlation with age.

Results: Results showed a slight positive correlation between PI and age, with a significant increase occurring during the acquisition of bipedalism. LL also increased with age, with notable postnatal development continuing into early childhood. Structural lordosis in the L4 and L5 vertebrae was evident in fetuses, indicating the presence of inherent lordosis in utero.

Conclusion: While PI exhibited minor changes after birth, LL development was strongly influenced by biomechanical factors associated with growth and bipedalism. These findings improve our understanding of the evolution of spino-pelvic anatomy and could guide therapeutic approaches for pediatric spinal deformities. Further longitudinal studies are needed to explore the genetic and biomechanical determinants of PI and LL development.