A Comparative Study of Surgical Correction of Idiopathic Scoliosis With Spinal Transpedicular Metal Structures in Children

A comparative study of surgical correction of idiopathic thoracic scoliosis using transpedicular spinal systems in children was performed. The study showed that using the transpedicular supporting elements along the entire length of the deformation (concave and convex sides) using the VCM (vertebral column manipulation) system, the correction was significantly better (p ≤ 0.05) than for the patients for whom the screws were not installed over two or more vertebrae from the concave side of the curvature, regardless of the magnitude of the spinal deformity. The kyphosis and lordosis were completely restored to their physiological values in all groups of patients.


INTRODUCTION
Surgical treatment of severe forms of thoracic idiopathic scoliosis remains an urgent and not fully resolved problem. Some surgeons perform surgical intervention exclusively with dorsal approach, using constructions with a large number of supporting elements (1)(2)(3), others use ventral systems to correct the deformity (4)(5)(6). A number of authors describe combined interventions from anterior and posterior sides of the spine, when dealing with idiopathic scoliosis (1,7). When correcting idiopathic scoliosis, it is important to restore the frontal and sagittal profiles of the deformed spine, rotate the apical vertebra and maintain this result in the postoperative period (8). Incorrect preoperative planning when choosing the level and length of fixation often leads to violation of the sagittal profile of the spinal column, which could lead to the development of kyphosis and degenerative processes (9).
In recent years, there is a tendency to use transpendicular spine fixation for the correction of spinal deformity in patients with idiopathic scoliosis (10). The preference toward this type of metal structures is explained by certain features and advantages over other systems. In the available studies, it has been proven that this system allows to achieve significant correction of deformity in all planes, stable fixation in the postoperative period, as well as limits the needs for extended instrumentation compared to the hook spinal systems (8,11). In addition, transpedicular multi-support hardware allows to prevent long-term loss of correction and deformity progression.
However, there is a discrepancy between different researchers regarding the results of such surgeries using multi-support systems with transpedicular support elements for patients with idiopathic scoliosis. Some authors claim that when correcting the curvature of the spine in patients diagnosed with thoracic idiopathic scoliosis, hybrid spinal systems are not inferior to transpedicular metal structures (12). Others prove the advantages and effectiveness of multi-support spinal metal structures with transpedicular supporting elements in comparison with hybrid systems (13,14). A number of surgeons note that when correcting spinal deformity with laminar and hybrid metal structures, restoration of the sagittal profile of the thoracic spine reaches physiologically correct values compared to when transpedicular spinal systems is used. According to their data, transpedicular metal structures contribute to the flattening of the kyphosis of the thoracic region following correction (15).

Aim
The aim of this study is to conduct a comparative analysis of the results of surgical correction of spinal deformity in children diagnosed with thoracic idiopathic scoliosis using transpedicular systems using various surgical methods.

MATERIALS AND METHODS
The work is based on the analysis of the results of surgical treatment of 80 children diagnosed with thoracic idiopathic scoliosis grade 3-4: 12 (15%) male patients and 68 (85%) female patients aged 14 to 17 years. In all children, right-sided curvature was observed. The type of scoliotic deformity was determined based on the Lenke classification (16). All patients (80 patients) were of the first type (Lenke 1); the sagittal contour in most of them was marked as normokyphosis. Patients were divided into 4 groups depending on the type of surgical correction. The choice of the technique used to correct spinal deformity in children with idiopathic thoracic scoliosis was determined by the initial size of the main curvature, its mobility, and the anatomoanthropometric features of the vertebral arch roots comprising the curvature arch.
All patients underwent X-ray of the spine in two standard projections and functional scans with lateral flexion. In order to determine the size of the vertebrae arch roots along the arch of deformity and the magnitude of rotation of the bodies of the apical vertebrae, computed tomography (CT) was performed. Spine X-ray and CT were performed both before and after the surgery in order to analyze the results of the surgical treatment. To exclude a pathology of spinal canal, an MRI was performed before the operation. Patients were monitored for the treatment effectiveness 6, 12, 18 months, and then once a year following the surgery. Statistical analysis was performed using the STATISTICA 6.0 software. When comparing pairs of groups for various characteristics in dynamics, paired Wilcoxon and Student's tests were used. When comparing independent pairs of groups, non-parametric Wilcoxon and Mann-Whitney tests were used. Samples' homogeneity was checked by the Kolmogorov-Smirnov test to confirm the normal distribution. P values of <0.05 were regarded as statistically significant.
The mobility of the deformity was calculated using the following formula: Standing scoliosis − Scoliosis with lean Standing scoliosis * 100 The percentage of scoliotic deformity correction was calculated using the following formula: Standing scoliosis before surgery − Standing scoliosis after surgery Standing scoliosis before surgery * 100 The percentage of apical vertebra derotation was determined according to the following formula:

DR =
Rotation before surgery − Rotation after surgery Rotation before surgery * 100 In the first group (20 patients with 40 • to 79 • Coob's angle and the mobility the main curve of more than 30%), the deformity correction was performed with a multi-support transpedicular hardware only from the dorsal approach with Halo-tibial traction. In this group of patients, transpedicular supporting elements were installed along the entire length of the deformity arch and the VCM (vertebral column manipulation) system was used at the apex in order to carry out a true derotation maneuver of the vertebral bodies. In the second group (20 patients with 51 • to 79 • Cobb's angle and the mobility of the main curve mora than 30%), the entire surgery was also performed using dorsal approach. We failed to put two or more screws on the concave side of the curvature due to small anatomical and anthropometric dimensions of the base of the vertebral arches in this group of patients. After the installation of transpedicular support elements, Halo-tibial traction was performed and the first rod, bent along the physiological curvature, was sequentially fixed in the support elements of the metal structure along the convex side of the deformity, while simultaneously correcting the kyphotic and scoliotic components of the deformity by applying direct pressure on the apex of the main arch, translational maneuver, and segmental compression. Subsequently, the second rod, bent along the physiological curvature, was placed in the supporting elements of the metal structure on the opposite side, and the final correction was performed using segmental distraction. The operation was concluded by putting a posterior bone graft. In the third group (20 patients with 80 • to 114 • Cobb's angle and the mobility of the main curvature of <30%), the surgical intervention was performed using two approaches (in 13 patients at the same time and in 7 patients in two stages). Using anterolateral approach, disepiphysectomy at the apex of the main deformity arch at the 4-5 levels in combination with corporodesis using dorsal approach, spinal deformity was corrected and stabilized with a multi-support transpedicular spinal system combined with Halo-tibial traction and dorsal fusion with autologous bone. For this group of patients, pedicle screws were installed along the entire length of the main curvature, and the VCM system was used to perform a true derotation maneuver of the vertebral bodies. In the fourth group (20 patients with 80 • to 148 • Cobb's angle and the mobility of the main curvature of <30%), surgical intervention was performed using two approaches (in 9 patients simultaneously and in 11 patients in two stages). Using anterolateral approach, Apical vertebral derotation, % 65.9 ± 9.5 Length of the metal structure, vertebrae (spondylodesis area) 11 ± 0.7 disepiphysectomy at the apex of the main deformity arch at the 4-5 levels in combination with corporodesis using dorsal approach, the curvature of the spine was corrected and stabilized with a multi-support transpedicular spinal system. We failed to install two or more screws on the concave side of the curvature due to the small size of the base of the vertebral arches. Corrective manipulations during the surgery in this group was similar to the technique used in the second group.

RESULTS
In the first group of patients, the angle of scoliotic deformity ranged from 40 • to 79 • (mean 54.   Length of the metal structure, vertebrae 11 ± 0.7 Length of the metal structure, vertebrae 12 ± 0.7   Apical vertebral derotation, % 22.7 ± 8.8 Length of the metal structure, vertebrae 13 ± 0.6  (Figure 3). The angle of kyphosis in the thoracic region is 30.2 • ± 8.5 • , the angle of lordosis in the lumbar region is 28.3 • ± 6.5 • . The  Table 4).
The percentage of the deformity correction using transpendicular spinal systems in our study is quite high in all groups of patients and the long-term angle loss is insignificant (from 0 to 4%).

DISCUSSION
When comparing the effectiveness of surgical correction between the first and second groups, the correction of scoliotic deformity of the spine in patients of the first group (92.1 ± 7.1%) was greater than in the second group (81.8 ± 6.3%). This can be explained by the use of two supporting elements placed in each vertebra (flexed and convex sides) included in the scoliotic arch. At the same time, it should be emphasized that the magnitude of derotation in the first group (65.9 ± 9.5%) is significantly higher compared to patients in the second group (23.2 ± 4.3%). This result is explained by the use of VCM system to achieve a true derotation of the vertebrae at the apex of the main curvature in the first group. The magnitude of the correction of kyphosis and lordosis in both groups was the same, and clinically and radiographically improvement or complete recovery was noted. Following mobilizing interventions on the anterior parts of the vertebral bodies of the main deformity curve from the anterolateral approach and dorsal correction with a metal structure with transpedicular supporting elements, it was noted that the magnitude of the correction of scoliotic deformity of the spine in the third group of patients (78.1 ± 7.7%) was greater than in the fourth group (71.7 ± 17.4%), which could be explained by the fact that installed transpedicular screws on both sides of the deformed area increase the effect on the spinal column. It should also be emphasized that the percentage of derotation of the apical vertebra in patients of the third group (46.3 ± 11.9%) was significantly higher than in the fourth group (22.7 ± 8.8%). This result was explained by the use of the VCM system to achieve a true derotation of the vertebrae at the apex of the main curvature in the third group.

CONCLUSION
Various options for the correction of spinal deformity in children with idiopathic scoliosis of the thoracic spine exist. Using different levels and lengths for installation of transpedicular elements, the sequence of corrective manipulations as well as the use of the VCM system made it possible to individualize the approach and to correct all components of the deformity in three planes. A conducted study on surgical treatment in patients with idiopathic scoliosis showed that using transpedicular support elements through the whole curvature arch with VCM system, was significantly better in correction of the deformity (Figure 5) (scoliotic arch and rotation of the apical vertebra), compared to those in whom pedicle screws were not installed over two or more vertebrae from the concave side of the curvature (Figure 6). The kyphosis and lordosis were completely restored to their physiological values in all groups of patients.