Surgical treatment of congenital hemivertebra scoliosis depends on the size and progression rate of the curvature. The degree of segmentation of the hemivertebra has a significant impact on progression. Completely segmented hemivertebrae have intact growth plates and typically progress more rapidly. As the main curvature increases, to balance the trunk, cranial and caudal compensatory curvatures progress simultaneously11. The purpose of surgical treatment is to correct the deformity and balance the trunk. Delayed surgery means a larger curvature angle and compensatory curvature angle, requiring a longer fusion segment for correction. Therefore, for patients with rapidly progressing hemivertebrae, early surgical intervention is necessary8. In this study, we focused on the corrective effect of hemivertebra resection and short segment fusion surgery and the influence of internal fixation on fused vertebra and spinal canal development.
Compared to other approaches, posterior hemivertebra resection and short segment fusion surgery have less trauma and a faster recovery time and are currently the most widely used surgical methods8,9. In our study, this procedure was used for all patients. Due to the relatively young age at which the patients underwent surgery before the progression of the scoliosis, the overall main curve Cobb angle was relatively small, with an average of 35°. The correction rate of surgery was 72.2%. Wedge osteotomy or complete removal of the hemivertebra can achieve a greater correction angle within a single segment, and smaller scoliosis angles and better intervertebral flexibility are beneficial for obtaining better corrective effects in short-segment fusion. During the follow-up period, although there was slight correction loss in some patients, it did not affect the overall outcome. The correction rates of the cranial and caudal compensatory curves were 67.28% and 74.17%, respectively. Due to the good flexibility of the pediatric spine, significant correction of compensatory curves can be achieved after sufficient correction of the structural curve.
In the correction of trunk balance, postoperative coronal balance was improved. The correction rate of CBD was 64.95%. In the analysis of SVA, thoracic kyphosis, lumbar lordosis, and local kyphosis, the average correction rate was relatively low and varied greatly among different patients. This may be because the segmental kyphotic deformity is not obvious in some patients, and the change in local kyphosis after surgery is relatively small. During follow-up, the CBD and SVA further decreased, which may be due to longer support brace treatment and spontaneous postural correction during growth10.
Only one case of the Adding-On phenomenon occurred during follow-up among all patients, which may be related to incomplete hemivertebra resection and a larger angle of UIV tilt11. The crankshaft phenomenon is a common complication after surgery in patients with immature skeletal development12. Because of the fixation effect of pedicle screws on three columns and only a single-segment fusion range, no obvious crankshaft phenomenon was observed in any patients after surgery.
Due to undergoing spinal internal fixation surgery at a young age, the spine has significant growth potential13. We evaluated the effect of internal fixation on the development of vertebral bodies within the fusion segment by measuring relevant parameters of the vertebral body and spinal canal, using adjacent vertebrae outside the fixed segment as a reference. The results showed that the growth rate of the width, length and height of the vertebral body within the fusion segment was slightly smaller than that of the upper and lower adjacent vertebrae outside the fusion segment. To better understand the development of vertebral bodies, we estimated the ratio of vertebral body volume at the last follow-up to that before surgery for the same vertebra. In our results, the volume of the upper instrumented vertebra increased by 72% and the lower instrumented vertebra by 67%, while the adjacent vertebrae outside the fixed segment had a greater change (92% for UNV and 74% for LNV). However, the one-way ANOVA showed a = 0.515 in the comparison of estimated values of different vertebral body volumes, indicating that although there were differences in the mean values, these differences were not statistically significant. This suggests that the inhibitory effect of internal fixation on vertebral development is relatively small. The vertebral bodies within the fixed segment also grew during the follow-up period, which might be the result of intact vertebral periosteum and at least one intact growth plate on either side14.
In addition, in the evaluation of spinal canal development, we measured the transverse and sagittal diameters of the spinal canal. The results showed that after a long-term follow-up, there was no significant change in the transverse and sagittal diameters of the spinal canal, which was much lower than the changes in the vertebral body. One-way ANOVA indicated that there was no statistically significant difference in the estimated value of the spinal canal area (Pa) among different vertebrae, further indicating that the effect of the internal fixation system on the development of the spinal canal is minimal. Pedicle screws pass through the neural central cartilage (NCC) that connects the pedicle and vertebral body. Previous studies13,15,16 have shown that the NCC of the thoracic and lumbar spine in children starts to close at 4–5 years old, and there is not much change in the size of the spinal canal from then until adulthood. In a study by Olgun et al.17, no negative effect of internal fixation on spinal canal development was observed during a two-year follow-up of children who had pedicle screws implanted before the age of 5. In this study, all patients who underwent surgery were over 3 years old. The spinal canal continued to enlarge slightly after internal fixation surgery; however, there were no cases of relative stenosis of the spinal canal or spinal cord compression caused by the restriction of internal fixation. There were no neurological dysfunctions observed in any of the patients after surgery or during follow-up.
There are certain limitations in this study. Some patients were too young before surgery and were unable to complete subjective assessments such as satisfaction with appearance before the operation. Additionally, all patients had their vertebral and spinal canal parameters measured using X-rays, which can cause some errors due to overlapping images. Although these errors have been shown to be negligible in other studies18, more accurate CT scans are difficult to perform universally during long-term follow-up.
In summary, posterior approach hemivertebra resection and short-segment fusion surgery can effectively correct scoliosis, and early surgery can save fusion range without significant loss of correction during follow-up. Although internal fixation surgery at a younger age has some inhibitory effects on spinal development within the fusion segment, it does not cause iatrogenic spinal canal stenosis or neurologic dysfunction. Therefore, posterior hemivertebra resection and short-segment fusion surgery is a safe and effective procedure.