Clinical Outcomes and Spinal Growth After Posterior Hemivertebra Resection and Short Segment Fusion in Children

Abstract

In order to evaluate the corrective effect of posterior hemivertebra resection and short-segment fusion surgery on pediatric patients and to assess the impact of short-segment fixation surgery on vertebral development during follow-up, a retrospective analysis was performed on 28 pediatric patients who underwent posterior hemivertebra resection surgery. The corrective effect was evaluated by comparing the preoperative, postoperative, and final follow-up Cobb angle, upper and lower compensatory curves and trunk balance. Meanwhile, the vertebral and spinal canal diameters of instrumented vertebrae and adjacent noninstrumented vertebrae were measured and compared between preoperative and final follow-up to assess the vertebral and spinal canal development. The correction rate of main curve Cobb angle was 72.2%. The estimated mean vertebral volume of the instrumented vertebra was slightly lower than that of the unfused segment at the final follow-up, but the difference was not statistically significant. The growth rate of the spinal canal during follow-up was much smaller than that of the vertebral body. Although internal fixation surgery might have a slight inhibitory effect on vertebral development within the fused segment in younger patients, it does not cause iatrogenic spinal canal stenosis or neurological dysfunction. Posterior hemivertebra resection and short-segment fusion surgery are safe and effective.

Introduction

Hemivertebra is a common cause of congenital scoliosis, which is a developmental defect formed during embryonic development^1,2. Most hemivertebrae have growth potential and can lead to scoliosis during growth, the degree of which depends on the type, location, and size of the hemivertebra. The resulting asymmetric spinal growth causes not only physical deformities but also psychological distress³.

Nonsurgical treatment has limited effectiveness for hemivertebrae, and most cases require surgical treatment⁴. Hemivertebrae can continue to progress with growth and can cause changes in adjacent vertebral structures, so surgery in the early stage is necessary to prevent local progression and the occurrence of secondary deformities⁵. Among them, posterior hemivertebra resection and short-segment fusion fixation surgery provide satisfactory corrective results and fusion stability, with less surgical trauma and fewer complications than other surgical methods.

Resection of the hemivertebra can significantly limit further progression of the deformity, and satisfying corrective and fixation effects can be achieved through a posterior pedicle screw fixation system⁶. Since the children who receive surgical treatment are relatively young, there is little literature on the impact of the internal fixation system on the development of the vertebral body and spinal canal in children during long-term follow-up.

This study is a retrospective study of patients who underwent hemivertebra resection and short-segment fusion surgery for more than 5 years. By measuring the Cobb angle of the scoliosis, compensatory curves above and below the affected area, local kyphosis, and trunk balance, the long-term efficacy of hemivertebra resection and short-segment fusion surgery was evaluated. In addition, by measuring the vertebral transverse diameter, sagittal diameter, vertebral height, spinal canal transverse diameter, and sagittal diameter, the impact of short-segment internal fixation surgery on vertebral and spinal canal development was assessed.

Results

Twenty-eight patients underwent posterior hemivertebra resection and short segmental fusion. The surgical duration was 120 min to 240 min, with an average of 160.71 min, and the blood loss was 150 ml to 400 ml, with an average of 219.64 ml. Due to the small amount of blood loss, no transfusions were recorded.

All patients were followed up for the long term after the surgery, with a minimum follow-up time of 5 years and a maximum of 9 years. The average follow-up time was 6.39 years. X-ray examinations were performed for all patients during the follow-up period.

The main curve Cobb angle was corrected from 35.49° preoperatively to 9.87° postoperatively, with a correction rate of 72.2%. At the last follow-up, the angle was 9.19°. The cranial compensatory curve was corrected from 12.79° preoperatively to 3.49° postoperatively, with a correction rate of 67.28%. The caudal compensatory curve was corrected from 18.17° preoperatively to 4.51° postoperatively, with a correction rate of 74.17%. The segmental kyphosis angle was corrected from 15.28° preoperatively to 3.99° postoperatively, with a correction rate of 84.85%. (Table 1)

Changes in vertebral body width: At the last follow-up, the VBW of the UIV increased by 10.21% compared to preoperative measurements, while the VBW of the LIV increased by 6.62%. The VBW of UNV increased by 11.13% compared to preoperative measurements, and the VBW of LNV had a growth rate of 11.29%. (Table 2)

Changes in vertebral body height: At the last follow-up, the VBH of the UIV increased by 32.77% compared to preoperative measurements, while the VBH of the LIV increased by 31.71%. The VBH of UNV increased by 37.98% compared to preoperative measurements, and the VBH of LNV increased by 31.60%. (Table 2)

Changes in vertebral body length: the VBL of the UIV increased by 16.69% compared to preoperative measurements, while the VBL of the LIV increased by 18.49%. The VBL of UNV increased by 22.25% compared to preoperative measurements, and the VBL of LNV increased by 15.07%. (Table 2)

Pv is an estimation of the change in vertebral body volume calculated by the ratio of the product of the diameters of the vertebrae at the last follow-up to the product of the preoperative diameters. Pv of different vertebrae: UNV: 1.92; UIV: 1.72; LIV: 1.67; LNV: 1.74. (Table 4)

Changes in spinal canal width: at the last follow-up, the CLAT of the UIV increased by 6.23% compared to preoperative measurements, while the CLAT of the LIV increased by 1.81%. The CLAT of the UNV increased by 11.28% compared to preoperative measurements, and the CLAT of the LNV increased by 8.15%. (Table 3)

Changes in spinal canal length: At the last follow-up, the CAP of the UIV increased by 5.04% compared to preoperative measurements, while the CAP of the LIV increased by 5.12%. The CAP of the UNV increased by 8.44% compared to preoperative measurements, and the CAP of the LNV increased by 5.92%. .(Table 3)

Pa is the ratio of the product of the CLAT and CAP at the last follow-up to that at preoperative, which estimates the change in the spinal canal area. Pa of different vertebrae: UNV: 1.18; UIV: 1.14; LIV: 1.08; LNV: 1.17.. (Table 4)

Among the 28 patients, two had postoperative superficial incisional infections. After treatment with intensified antibiotics, wound dressing changes, and nutritional support, both cases were cured. During the follow-up period, only one case showed an adding-on phenomenon, but due to its small angle, there was no obvious change in appearance, and a second surgical intervention was not considered. No neurological dysfunction was observed in any of the patients. (Fig. 2, 3)

Discussion

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 methods^8,9. 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 studies^13,15,16 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.

Methods

We confirm that all methods were carried out in accordance with Declaration of Helsinki and its later amendments, and all protocols were approved by the Ethics Committee of Xiangya Hospital of Central South University (ethics approval number: 201703359). We confirm that written informed consent was obtained from all subjects.

Declarations

Acknowledgements

The work was supported by the Hunan Province Natural Science Foundation of China (No. 2020JJ4913), Research project on postgraduate education and teaching reform of Central South University (No. 2021JGB082), Graduate course ideological and political construction project of Central South University (No.2022YJSKS032) .

Author contributions

Hongqi Zhang designed the study; Yu-Xiang Wang collected and analyzed the data; Yuxuan Du collected and analyzed the data, and wrote the manuscript.

Data availability

Some or all data, or code that support the findings of this study are available from the corresponding author upon reasonable request. 

Additional information 

Competing interests

 The authors declare no competing interests.

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