Evaluation of Predictors and Outcomes of Bracing with Emphasis on the Immediate Effects of in-Brace Correction in Adolescent Idiopathic Scoliosis

Abstract

Background:

Adolescent idiopathic scoliosis (AIS) is defined as a lateral curvature of the spine of unknown etiology with a Cobb angle of greater than 10 degrees with vertebral rotation. Bracing, specifically with a rigid thoracolumbosacral orthosis (TLSO), decreases the risk of curve progression to over 50 degrees, the threshold for surgical intervention. Some authors have suggested that 30-50% in-brace correction of the Cobb angles is required to prevent significant curve progression. The purpose of the study is to evaluate the current bracing protocol at the University of Iowa as a quality control exercise for the treatment team.

Methods:

AIS patients (n = 61; 8 male, 53 female) who received a Rosenberger TLSO at the University of Iowa Department of Orthopaedics and Rehabilitation from 2016-2017 were included in the study. Inclusion criteria include presence of pre-brace and in-brace x-rays within 3 months of initiating brace treatment. Patients with other diagnoses were excluded. Radiographic indicators of brace effectiveness, such as the Cobb angle, were measured.

Results:

The in-brace x-rays of 46 (76%) patients showed less than 30% correction. Minimal changes from the pre- to in-brace x-ray were observed in other radiographic measures.

Conclusions:

Results indicate that if the 30-50% correction recommended by the literature is valid, then modifications to the process of measuring, fabricating or modifying our current TLSO’s for AIS are warranted.

Level of evidence: III

Introduction

Adolescent idiopathic scoliosis (AIS) is defined as a lateral curvature of the spine of unknown etiology with a Cobb angle of greater than 10 degrees with vertebral rotation.¹ The prevalence of AIS is approximately 3% in children under the age of 16, with 0.3-0.5% having worsening curves requiring treatment.² Bracing, specifically with a rigid thoracolumbosacral orthosis (TLSO), has been shown to decrease the risk of curve progression to over 50 degrees, one commonly used threshold for surgical consideration.¹ Preventing surgery through effective bracing is an important goal not only for patients, but also for the United States healthcare system. In 2012, spinal fusion for AIS resulted in the highest aggregate (approximately $341 million) costs for procedures in children between the ages of 10 and 14.³

Given a patient’s baseline characteristics (e.g. magnitude of the curvature and skeletal maturity) the two most important factors thought to be associated with bracing success are the amount of correction obtained in the brace, and the number of hours of wear time per day.^1,4,5 The literature suggests braces must correct the curve by at least 30-50% in order to prevent significant curve progression.^6,7,8 In addition to correction of the coronal Cobb angle, components of the deformity (e.g. kyphosis, lordosis, coronal compensation) are increasingly being considered. For example, hypokyphosis independent of pelvic parameters is common in AIS and is associated with decreased pulmonary function.^9,10 Sagittal imbalance, particularly seen in spinal fusion patients, leads to increased cervical and lumbar complications, including low back pain.¹⁰ Surgical correction in the coronal and sagittal planes have beneficial effects on center of mass and center of pressure, ultimately improving gait.¹¹ Apical vertebral rotation is an important prognostic factor for curve progression in both thoracic and lumbar curves.^12,13

The purpose of the study is to evaluate the immediate (in-brace) outcomes of a recent sample of patients being treated for AIS. Specifically, we analyze the amount of correction achieved in the brace at the beginning of treatment and compare it to recommendations from the literature.

Methods

Participants

AIS patients who received a Rosenberger TLSO brace at the University of Iowa Department of Orthopaedics and Rehabilitation from 2016-2017 and had both pre-treatment radiographs and a radiograph in the brace within 3 months were included. Exclusion criteria include patients receiving a TLSO for a diagnosis other than AIS.

Data Collection

Demographics were collected from the medical record. The pre-treatment hand, posterioranterior and lateral full-spine, and the in-brace radiographs were downloaded for measurement. The Cobb angle(s), thoracic kyphosis, lumbar lordosis, apical vertebral rotation, sagittal balance, and coronal balance were measured by the first author and spot-checked by the third author for accuracy. The Risser grade and Sanders skeletal maturity score (SSMS) were measured to assess skeletal maturity.^14,15

Data Analysis

Summary statistics included the mean with standard deviation, median, range, and 95% confidence intervals. The obtained measurements were compared to the ranges of normal (Table 1). Data analysis was performed using Microsoft Excel (2016).

Table 1.

Definitions of Normal for Radiographic Measurements

	Definitions
Thoracic kyphosis	20 to 45 degrees
Lumbar lordosis	< 45 degrees
Apical vertebral rotation	≤ 5 degrees
Sagittal balance	< 5 cm deviation
Coronal balance	≤ 2 cm deviation

Results

Data and images from a total of 61 patients (8 male, 53 female) with a mean age of 12.81±1.37 years were extracted from the EPIC™ medical record and included in the study (Table 2).

Table 2.

Demographics of AIS patients

	Mean with SD	Median	Range
Age	12.8 ± 1.4	12.7	12.7 - 17.1
Height (cm)	158.0 ± 9.2	158	131.3 – 180.1
Height percentile	64.3 ± 26.8	71.0	1.3 – 99.6
Weight (kg)	46.7 ± 12.0	44.0	27.2 – 97.3
Weight percentile	52.0 ± 27.1	52.5	2.1 – 99.6

Pre-brace vs. in-brace radiographic measurements

Most of the patients were skeletally immature, with 59% at less than Risser 2 and 59% had an SSMS bone age less than 4. The mean Cobb angle of the largest curve prior to treatment was 27.98±7.32 degrees compared to 22.46±7.96 degrees in-brace (Table 3). The average curve correction was 5.5 degrees. The in-brace correction in 48% of patients was less than 15%, 28 % was between 15-30% correction, 16% with 30-50% correction, and 8% had over 50% correction (Figure 1). The coronal balance was restored in the brace in 5% of patients, whereas it continued to be abnormal 5% and 5% of patients became decompensated in the brace (Table 4). The average change in coronal balance was 3.2 x 10-2 cm. 82% had normal sagittal balance (< 5 cm deviation) initially and in-brace, with only 10% of patients improving from abnormal to normal and 5% worsening. The average change in sagittal balance was 0.35 cm. The thoracic kyphosis was within normal range (20 to 45 degrees) in 61% of patients both at baseline and in the brace, 16% became hypokyphotic, and kyphosis was increased into the normal range in 13%. The average change in kyphosis was 1.8 degrees. 61% of patients were hyperlordotic at baseline and in-brace, 21% improved from hyperlordotic to normal (less than 45 degrees), while lordosis increased in 8% who became hyperlordotic. The average change in lordosis was 3.1 degrees. Apical vertebral rotation was consistently normal (5 degrees or less) both pre-brace and in-brace in 36% of patients; 3% developed abnormal rotation and rotation was decreased in 13% (improved from abnormal to normal). The average change in apical vertebral rotation was 2.6 degrees.

Table 3.

Mean with Standard Deviation (range) and Average Change of Pre-Brace and In-Brace Radiographic Measurements

	Pre-brace	In-brace	Average Change
Cobb (degrees) angle	28.0 ± 7.3 (10-43)	22.5 ± 8.0 (5-41)	5.5 ± 6.0
Thoracic (degrees) kyphosis	29.0 ± 10.1 (7-55)	27.2 ± 9.2 (4-46)	1.8 ± 7.2
Lumbar (degrees) lordosis	54.0 ± 10.1 (28-80)	50.9 ± 9.3 (27-72)	3.1 ± 8.4
Apical rotation vertebral (degrees)	10.5 ± 6.9 (0-30)	8.4 ± 6.8 (0-30)	2.1 ± 4.8
Sagittal (cm) balance	2.6 ± 1.8 (0.1-6.3)	2.2 ± 1.6 (0.4-1.6)	0.35 ± 2.1
Coronal (cm) balance	1.4 ± 0.9 (0.1-3.9)	1.3 ± 1.2 (0.1-4.6)	3.2 ± x 1.1 10-2
Risser	59% less than 2 (0-4)	-	-
Sanders	59% less than 4 (2-6)	-	-

Figure 1.

Distribution of in-brace percent correction (Initial Cobb angle – in-brace angle)/Initial Cobb angle*100.

Table 4.

Number and Percentage of Patients with Radiographic Changes from Pre-Brace to In-Brace

	Maintained Normal Range	Became Abnormal in the Brace	Became Normal in Brace	Remained Abnormal
Thoracic kyphosis	37 (61%)	10 (16%)	8 (13%)	6 (10%)
Lumbar lordosis	6 (10%)	5 (8%)	13 (21%)	37 (61%)
Apical vertebral rotation	22 (36%)	2 (3%)	8 (13%)	29 (48%)
Sagittal balance	50 (82%)	3 (5%)	6 (10%)	2 (3%)
Coronal balance	46 (75%)	6 (10%)	3 (5%)	6 (10%)

Discussion

Previous studies have shown that Cobb angle correction with a TLSO significantly influences curve progression. Katz et al. (2001) showed that a 25% or greater in-brace Cobb angle reduction was associated with a 73% success rate (curve progression of <6 degrees) in a study of Boston braces.¹⁶ Similarly, Emans et al. (1983) found that the greater the in-brace Cobb angle correction, the better the outcome, suggesting a goal of 50% correction to halt curve progression.⁶ In a retrospective study, Landauer et al. (2003) showed that over 40% curve correction was significantly related to successful outcomes in patients using a Chêneau-type brace.⁸ Goodbody et al. (2016) found that 45% or greater in-brace correction was associated with bracing success.⁷ The braces in our study fell short of these standards, as only 24% resulted in more than 30% correction. It must be acknowledged, however, that the achievable in-brace correction is likely limited by the flexibility of the curve, amount of vertebral rotation, skeletal maturity and other factors. In literature, both the SSMS bone age and Risser stage is significantly correlated with curve progression.¹⁷ Additionally, the contribution of in-brace correction to the final result relative to other factors such as maturity, curve pattern and wear time has not been established. Little change was observed in the other radiographic parameters associated with AIS. New Computer Aided Design and Computer Aided Manufacturing (CAD/CAM) techniques have allowed a 3D approach to designing braces that could improve other parameters, such as kyphosis, lordosis, and coronal balance, along with Cobb angles.18 With the CAD/CAM system, the optimal brace shape and placement of pressure pads for immediate in-brace correction can be simulated.¹⁸ These findings indicate that substantial changes should be instituted in our bracing program. Modifications to the measurement system, the fabrication process, and or the fitting adjustments of our braces should be instituted.

The limitations of this study include a small sample size and the fact that changes may have been made to the orthosis after review of the in-brace x-ray. Modifications were not immediately followed by an additional in-brace x-ray, therefore, the measurements here might not accurately reflect the corrective forces of the brace after that point.

Future research could track wear time and curve progression all the way to skeletal maturity in addition to obtaining radiographic measurements. Because of this study, patients with AIS at the University of Iowa are scheduled to see the prosthetist before all x-rays and clinic appointments to ensure optimal brace fit. Posteroanterior and lateral x-rays are required at brace delivery and repeated at six weeks per standard of care. Further studies performed after these adjustments will assess whether or not effective in-brace Cobb angle correction is now achieved in AIS patients.