The Effects of Bracing on Pelvic Parameters in Adolescent Idiopathic Scoliosis

Background: This study aims to evaluate the effects of bracing on the Cobb’s angle (CA) and spinopelvic parameters in adolescent idiopathic scoliosis (AIS) patients. Methods: A total of 51 AIS patients who received bracing treatment between January 2018 and August 2019 were retrospectively analyzed. The pro-bracing and in-bracing radiographs were analyzed with regard to the spinopelvic parameters. The CA, pelvic coronal obliquity angle (PCOA), thoracolumbar kyphosis (TK), lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), sagittal vertical angle (SVA) and coronal vertical angle (CVA) were measured. Results: The mean age at the initiation of bracing was 13.6 ± 1.5 years. The mean pro-bracing CA was 24.0° ± 6.3°. There were no statistically signicant differences between pro-bracing and in-bracing measurements of SVA and CVA. However, there were statistically signicant differences between the pro-bracing and in-bracing measurements of the CA, PCOA, TLK, LL, PT and SS. A signicant correlation was observed between PT variation and TLK variation in the sagittal plane. In the coronal plane, the PCOA variation was correlated to pro-bracing PCOA. Conclusion: Bracing effects of AIS can be extended to the pelvis. The pelvis should retro-rotate correspondingly to TLK hypokyphosis on sagittal plane, whereas in coronal plane, pelvic obliquity was improved independently.


Introduction
AIS is a three-dimensional deformity characterized by coronal, sagittal, and rotational deformities of the spine [1]. For moderate deformities, bracing is the most common treatment. Its e ciency in preventing the progression of curves is generally admitted [2].
In the most previous studies on bracing of AIS patients, CA was the main index used to evaluate the treatment effectiveness [3]. Recently, addition to the CA, other factors such as the curve pattern, LL, and pelvic parameters, have been taken into consideration for the evaluation of the outcomes of bracing in AIS [4,5].
Scoliosis is often associated with pelvic parameters [6], It has been shown that patients with AIS have an abnormal spinopelvic balance and pelvic morphology. Walker and Dickson [7] screened 5303 schoolchildren aged 10-14 years old for scoliosis. Three hundred seventy-ve (7.1%) children had curves of 5-9° inclusive and, of these, 138 (36.8%) had scoliosis secondary to a pelvic rotation. Pelvic rotation in AIS patients could be explained in part from a traction phenomenon created by paraspinal or abdominal muscle tension [8].
An evaluation of variation of pelvic parameters can provide a better understanding of the brace mechanisms of action in controlling the curve progression. Furthermore, a signi cantly higher prevalence of pelvic rotation was observed in patients with thoracolumbar curves, than in thoracic curves. So we aimed to evaluate the effects of bracing on pelvic parameters in thoracolumbar AIS.

Materials And Methods
Approval of this retrospective study was obtained from the Second Central Hospital of Baoding. The medical records of eligible patients with AIS who underwent Chêneau bracing between January 2018 and August 2019 in our department were reviewed retrospectively. We excluded patients with congenital scoliosis, syndromic scoliosis, structural leg discrepancies, and patients aged 16 or more at the time of bracing.
Inclusion criteria for the indication of brace were: Lenke5 AIS skeletal immaturity, premenarcheal or postmenarcheal by less than 1 year, a CA between 15° and 45°. receiving Chêneau brace ( Figure 1); having ongoing bracing treatment for at least six months prior to study.

Radiographic assessment
Standing whole spine radiographs were ensured that patients were completely erect and their pelvis was not rotated. Radiological parameters were measured from anteroposterior and lateral standing radiographs of whole spinal, which were obtained pro-bracingly and in-bracingly. All of the measurements were performed by Surgimap Spine Software New York, USA). Measurements were all conducted by two investigators independently and blinded to the clinical information to avoid bias. The list of patients for measurement were randomly allocated and provided by another investigator. An average score was used for any measurement with < 5 degrees of difference. Any difference beyond 5 degrees was discussed between the investigators with a nal consensus on the measurement used for analysis. The cutoff of 5 degrees was used based on documented radiographic measurement errors in a scoliotic curve.
The spinopelvic parameters of pro-bracing and in-bracing radiographs were used to assess: CA de ned as the angle between the perpendicular lines from the upper endplate of the most tilted superior vertebra and lower endplate of the most tilted inferior vertebra. The pro-bracing and in-bracing radiographs of the patients were used to assess these parameters.

Statistical Analysis
The data was analyzed using SPSS Statistics 25 (IBM Corp, Armonk, NewYork, USA) Shapiro-Wilk test found that the data was normally distributed. Paired t-test was used to compare pro-bracing and inbracing spinopelvic parameters. The Pearson correlation analysis was used to identify the relationships between the variations in the spinopelvic parameters. P < 0.05 was considered statistically signi cant.
Pro-bracing and in-bracing spinopelvic parameters comparement Table 1 shows pro-bracing and in-bracing measurements of the sagittal parameters. According to the results, the TLK, LL, PT, SS had statistical signi cance (p<0.05) ( Table 1). Table 2 shows the pro-bracing and in-bracing measurements of the coronal parameters, the CA and PCOA were statistically signi cant (p<0.05) ( Table 2).

Correlation analysis on variation of spinopelvic parameters
The correlation analysis on sagittal parameters variation was shown in Table 3. In the sagittal plane, PT variation had mild correlations with the TLK variation, whereas there was no statistically signi cant relationship between the other spinopelvic parameters and TLK values. The correlation analysis of coronal parameters variation were shown in Table 4. In the coronal plane, the PCOA variation was corelated to pro-bracing PCOA. However, CA variation had no statistically signi cant correlation with PCOA variation.

Discussion
Scoliosis changes the spinal column in all three anatomical planes; therefore, all of the spinopelvic parameters are affected [9]. Restoring the balance in the spinopelvic parameters is an important aspect of AIS treatment, especially for Lenke5 AIS [10]. In these patients under bracing treatment, the sagittal and coronal rotation of pelvic is integrant to regulate the spinopelvic malalignment.
Most of bracing studies performed on the AIS were focused on the CA behavior and the goal of bracing treatment is to control the curve progression [11,12,13]. However, there is no study which assesses the behavior of pelvic parameters in patients with scoliosis under bracing treatment. The results of the current study showed that the Chêneau bracing treatment did not have statistically signi cant effects on the whole balance parameter such as CVA and SVA, although it showed statistically signi cant effects on regional spinopelvic parameters such as CA, PT, SS, TLK, LL and PCOA. In a subsequent correlational analysis, there was no signi cant correlation between the variation of CA and the pelvic parameters. Therefore, our hypothesis regarding the direct effects of bracing on the pelvic parameter values was accepted.
The CA has been used as a main factor to determine the brace treatment effectiveness in AIS cases. In the present study, the mean degree of curve correction was 57.1% which was statistically signi cant between baseline and nal measurements. This result is also in line with the study of Katz and Durrani [14] which found that a minimum of 25% correction of the primary scoliosis curve was needed to predict the positive outcome of brace treatment in AIS patients. Although it showed no statistically signi cant correlation between the pelvic parameter and corrective rate of CA, the rotational pelvic parameters were directly affected by brace treatment.
As sagittal rotational parameters of pelvis. The increased PT combined with decreased SS constituted the evidence of pelvic posterior rotation in the present study. In the subsequent correlation analysis, a negative correlation between TLK and PT was observed. Whereas correlation between TLK and LL was absent. This phenomenon suggests that the reduced TLK caused by corrective forces of braces is compensated by pelvic retro-rotation.
In prior study [15], there was a signi cantly higher prevalence of pelvic obliquity was observed in patients with lumbar curves, such as Lenke types 5 and 6, than in thoracic curves, such as Lenke types 1 and 2. Pelvic obliquity can be assessed by its anatomical origin, whether it is caused by a suprapelvic, intrapelvic, or infrapelvic problem or any combination of these problems [16]. Suprapelvic cause is secondary to the spinal deformity in which scoliosis may drive the pelvis into an asymmetrical position.
In the present study, we observed a positive relationship between original PCOA and variation of PCOA.
This mean that the more tilted toward the concave side of the lumbar curve the pelvis, the more in uenced on pelvic obliquity of bracing. Bracing treatment could correct the scoliosis as well as pelvic obliquity simultaneously.
Nonetheless, this study had several limitations. Some of which are signi cant to the conclusions we are able to reach. The retrospective nature, as well as small cohort, make it di cult to draw de nitive conclusions. Additionally, the short-term effects of bracing were analyzed for them. Although previous studies [17] showed that there was a signi cant correlation between immediate in-brace correction and outcome of brace treatment in AIS, long-term studies should be performed to evaluate the effect of immediate in-brace changes of pelvic parameters on outcome of brace treatment in AIS. Furthermore, the spinal axis radiographs were not centered on the pelvis and, therefore, there could be some parallax effect in the measurement of the pelvic parameters.

Conclusions
Bracing effects of AIS can be extended to the pelvis. The pelvis should retro-rotate correspondingly to TLK hypokyphosis on sagittal plane, whereas in coronal plane, pelvic obliquity was improved independently.