Age-specific normative values of sacral development and fusion in children and adolescents: a cross-sectional study utilizing multiplanar reconstruction computed tomography imaging

Abstract

Background: This study aimed to determine the index of the sacral vertebrae fusion period in children and adolescents to diagnose the lesion around the sacral spine accurately.

Methods: Patients aged 0-40 years who underwent computed tomography (CT), including the normal sacrum for screening abdominal disorders and pan-scan in trauma between 2019 and 2022 were retrospectively examined. There were 402 eligible sacra (385 patients: 206 women and 179 men). We evaluated bony fusion at six parts of the sacral vertebrae (anterior or posterior of each intervertebral and both side lateral masses). The predicted probability of bony fusion obtained from the logistic regression model is depicted graphically by sex.

Results: The association between bony fusion in each vertebral segment and age was evaluated using a logistic regression model with a Huber-White robust sandwich estimator, including the patient as a clustering variable. Bony fusion of the sacral bodies of S1/S2 was slowest, with 80% of patients achieving bony fusion at 28.7 and 24.6 years of age for men and women, respectively. Compared to men, women exhibited earlier fusion of the intervertebral segments of the sacral vertebrae; however, no significant difference between the sexes in terms of eventual bony fusion at the lateral mass was observed, while the initiation of bony fusion occurred earlier in women.

Conclusion: The predicted probability of bony fusion could aid pediatricians, orthopedists, radiologists, and other physicians in understanding the normal development of the sacral spine and accurately differentiating the lesion around the sacral spine.

Keywords: Adolescent; Bony fusion; Sacral spine development; Sacrum.

Fig. 1

Flow diagram of patient selection. Patients undergoing CT between February 2019 and November 2022 were included. The data of patients who underwent imaging of the pelvic region were extracted, and 11 patients were excluded. Finally, 402 eligible CT images were included

Fig. 2

Sex and age distribution of the 402 sacra. This figure depicts the sex and age data for the 402 study patients

Fig. 3

Predicted probability of sacral fusion by age for each lateral mass. The S1/S2 vertebrae fusion showed the slowest bony fusion progression compared with the other vertebrae. Significant changes by sex were observed in S2/S3 and S4/S5, indicating that the initiation of bony fusion is earlier in female vertebrae than in male vertebrae (interaction p-values of < 0.001 and 0.006, respectively)

Fig. 4

Predicted probability of sacral fusion by age and lateral mass segment. The process of bony fusion of the anterior surface of the lateral masses is depicted in a–c, while d–f illustrates the process of bony fusion of the posterior surface of the lateral masses. In all vertebral segments, the age at the beginning, progress, and completion of bony fusion remained consistent between the anterior and posterior surfaces

Fig. 5

Predicted probability of sacral fusion by age for each vertebra on the anterior surface. This figure illustrates the relationship between intervertebral space and sacral fusion rate, showing that a higher intervertebral space from S3/S4 results in slower fusion. It also demonstrates a significant interaction between age and sex, with women completing bony fusion earlier at the S2/S3 level and in the lateral masses

Fig. 6

Predicted probability of sacral fusion by age at each vertebra on the posterior surface. The posterior and anterior vertebrae require approximately 10 years for the bony fusion of S2/S3 and S1/S2. There is no significant interaction between age and sex in either of the vertebral segments. The female group exhibited significantly faster bony fusion progression in the S3/S4 vertebrae and anterior vertebral body (p = 0.024) than male group

Fig. 7

Three-dimensional computed tomography (3D-CT) images depicting normal sacral development with Risser’s sign. At 6–9 years of age, almost no fusion was observed in any intervertebral space in males. By 10–12 years of age, essentially no fusion was observed in any intervertebral space in males; however, in females, fusion was observed in many cases in the lower intervertebral spaces. At 13–15 years of age, fusion was observed in the lateral masses of each vertebral intervertebral space in females, and at 16–18 years of age, fusion was observed in the lateral masses of all vertebral intervertebral spaces in most patients. At approximately 25 years of age, most patients of both sexes exhibited fusion at all sites of intervertebral masses