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Do Heavier Patients With Adolescent Idiopathic Scoliosis Have More Preserved Thoracic Kyphosis and Pulmonary Function?
Spine Deformity 6 (2018) 704e706 www.spine-deformity.org
Do Heavier Patients With Adolescent Idiopathic Scoliosis Have More Preserved Thoracic Kyphosis and Pulmonary Function? Robert Tung, BSa, Mason Uvodich, BSa, John T. Anderson, MDb,*, Katie Carpenter, CPNP-PCb, Ashley Sherman, MAb, Rafael Lozano, MDc a
University of Kansas School of Medicine, 3901 Rainbow Blvd, Kansas City, KS 66160, USA b Children’s Mercy-Kansas City, 2401 Gillham Rd, Kansas City, MO 64108, USA c Department of Surgery, University of Nevada, Las Vegas, 4505 S. Maryland Pkwy, Las Vegas, NV 89154, USA Received 18 January 2018; revised 3 May 2018; accepted 5 May 2018
Abstract Study Design: Retrospective. Objectives: We aimed to determine if heavier patients with adolescent idiopathic scoliosis (AIS) had more preserved thoracic kyphosis (TK), and as a result, more preserved pulmonary function. Summary of Background Data: Some believe that childhood weight is predictive of adult sagittal plane parameters, with heavier children having greater TK as adults. Generally, thoracic scoliosis is coupled with loss of TK, which is associated with worsening pulmonary function. Methods: A total of 142 patients with AIS and a structural main thoracic curve were analyzed. We excluded patients with structural proximal thoracic curves (Lenke 2 and 4). Standing preoperative radiographs, pulmonary function tests, and preoperative body mass indices (BMIs) were reviewed. The main thoracic Cobb angle, T2eT12 TK, percentage predicted forced vital capacity (FVC) and BMI were recorded. Spearman correlation was determined. Linear regression analysis used FVC as the primary outcome and BMI, TK, and Cobb angle as the independent variables. BMI categories were overweight/obese (BMI >25) and normal (BMI !25). Wilcoxon rank-sum tests were performed to detect a difference in TK and BMI between the 2 groups. The Cobb angles between the two groups were analyzed by t tests. Results: Demonstrated correlations included BMI and FVC (0.37, p <.01), FVC and TK (0.26, p !.01), BMI and TK (0.23, p 5 .01), and FVC and Cobb angle (e0.23, p 5 .01). Linear regression revealed that Cobb angle (p <.01), TK (p !.01), and BMI (p !.01) remained statistically significant predictors of FVC. Wilcoxon rank-sum tests revealed a statistically significant difference between TK (p 5 .03) and FVC (p !.01) in the overweight/obese group and the normal group, with the overweight/obese group having greater values for both TK and FVC. The Cobb angles between the overweight/obese and normal group were not significantly different (p 5 .72). Conclusions: Heavier AIS patients have greater values of TK and percentage predicted FVC. Level of Evidence: Level III. Ó 2018 Scoliosis Research Society. All rights reserved. Keywords: AIS; Adolescent Idiopathic Scoliosis; Scoliosis; Obesity; Pulmonary function
Introduction Author disclosures: RT (none), MU (none), JTA (paid speaker at an American Academy of Pediatrics CME course), KC (none), AS (none), RL (none). Reviewed and approved by the Pediatric IRB at The Children’s Mercy Hospital & Clinics (IRB No. 16010073). No funding was received for the purpose of this study. *Corresponding author. Orthopaedic Surgery, University of MissouriKansas City School of Medicine, Children’s Mercy-Kansas City, 2408 Gillham Road, 2nd floor Annex, Kansas City, MO 64108, USA. Tel.: (816) 234-3075; fax: (816) 302-9743. E-mail address: [email protected] (J.T. Anderson).
Adolescent idiopathic scoliosis (AIS) is a threedimensional skeletal deformity of the spine affecting up to 3% of the population. Although typically benign, the natural progression of AIS may result in disturbances of body that affect morphology and physiology. AIS patients are at greatest risk of progression during the pubertal growth spurt. In general, thoracic scoliosis creates hypokyphosis. Studies have shown a correlation between thoracic
2212-134X/$ - see front matter Ó 2018 Scoliosis Research Society. All rights reserved. https://doi.org/10.1016/j.jspd.2018.05.007
R. Tung et al. / Spine Deformity 6 (2018) 704e706
hypokyphosis and worsening pulmonary function in children with AIS. Newton et al. described a positive association between thoracic kyphosis and forced vital capacity. Clinically relevant decreases in forced vital capacity are correlated with larger thoracic curves and with thoracic hypokyphosis [1-3]. The role of BMI in these patients is of importance because data suggest childhood obesity can affect adolescent spinal sagittal plane parameters [4]. Children with higher BMI will develop greater thoracic kyphosis compared to children with lower BMIs. In the senior author’s experience, children with AIS with normal to above normal thoracic kyphosis, have more persevered FVC% and higher BMIs than their hypokyphotic peers. This has implications when counseling parents about the pulmonary aspects of the disease and the indications for surgical intervention. Materials and Methods A retrospective Level III study of preoperative variables was conducted. These data included radiographs, pulmonary function testing (PFT) data, and BMI measurements of a consecutive series of AIS patients cared for by three different surgeons at a large tertiary children’s hospital from January 1, 2009, to January 1, 2016. Subjects included in this study were between ages 10 and 18 years and had a Cobb angle of greater than 50 degrees. All data were extracted from studies and measurements obtained during the preoperative visit. Patients with scoliosis not diagnosed as AIS or with underlying asthma or other known pulmonary disease, not directly attributed to their scoliosis, were excluded. Patients with a history of a previous thoracotomy or sternotomy; those who had an isolated thoracolumbar curve; those with a structural proximal thoracic curve; and patients with inadequate imaging, BMI, or PFT data were also excluded. Thoracic Cobb angle and the T2eT12 sagittal Cobb angle were measured using InteleViewer software. The percentage predicted FVC and BMI of each subject was obtained from the subject’s medical records. Spearman correlation was determined. Linear regression analysis was performed using FVC as the primary outcome and BMI, TK, and Cobb angle as the independent variables. BMI was dichotomized as overweight/obese (BMI>25) and normal (BMI !25). Wilcoxon rank-sum tests were performed to detect a difference in TK and FVC between the two groups. The Cobb angles between the two groups were analyzed by t tests. Alpha was set at 0.05 and power analysis was performed to a power of 0.80. Results Table 1 summarizes patient demographics. Our database generated 203 AIS patients that met our inclusion criteria. Of these patients, an additional 61 were excluded. The 142
705
Table 1 Patient demographics. 203 61 14 59.3 34.7 21.9 83.4
Total patients reviewed, N Patients excluded, mean Age (years), mean Thoracic Cobb angle (degrees), mean TK (degrees), mean BMI, mean %FVC, mean
BMI, body mass index; FVC, forced vital capacity; TK, thoracic kyphosis.
Table 2 Wilcoxon rank-sum for preobese/obese versus others. BMI >25 BMI !25
TK*, median (IQR)
FVCy, median (IQR)
39 (12) 33 (19)
91 (20) 80.6 (22.1)
BMI, body mass index; FVC, forced vital capacity; IQR, interquartile range; TK, thoracic kyphosis. * p 5 .03 for TK between the two groups. y p !.01 for FVC between the two groups.
AIS patients included for analysis had an average age of 14 years, Cobb angle of 59 , thoracic kyphosis of 35 , BMI of 21.9, and FVC% of 83. BMI, TK, and FVC were all positively correlated at a statistically significant level. A statistically significant negative correlation was found between FVC and Cobb angle (e0.23, p 5 .01). Of the variables, the strongest correlation was found between BMI and FVC (0.37, p<.01) followed by FVC and TK (0.26, p !.01) and FVC and Cobb angle (e0.23, p 5 .01). Linear regression revealed that Cobb angle (p<.01), TK (p !.01), and BMI (p !.01) all remained statistically significant predictors of FVC (R2 5 0.26). The coefficient of determination was e0.53 (95% confidence interval e0.76, e0.29) for Cobb angle, 1.04 for BMI (95% confidence interval 0.52, 1.55), and 0.31 for TK (95% confidence interval 0.16, 0.47). Wilcoxon rank-sum tests revealed a statistically significant difference between TK (p 5 .03) and FVC (p !.01) in the overweight/obese group (n 5 27) and the normal group (n 5 115), with the overweight/obese group having greater values for both TK and FVC (Table 2). The Cobb angles between the overweight/obese and normal groups were not significantly different (p 5 .72). Discussion We sought to identify associations between BMI and pulmonary function in adolescents with idiopathic scoliosis. Our major finding was that greater values of BMI and TK were correlated with better pulmonary function, as defined by a higher FVC. BMI and TK were correlated to a lower degree than their individual relationships to FVC. Also, they contributed independently to FVC percentage, with linear regression suggesting that the relationship of BMI to FVC may not be entirely mediated through TK.
706
R. Tung et al. / Spine Deformity 6 (2018) 704e706
The correlation between thoracic spinal deformity in AIS and decreased pulmonary function has been suggested in previous research. Newton et al. found the magnitude of the thoracic curve, number of vertebrae involved in the thoracic curve, thoracic hypokyphosis, and coronal imbalance to be associated with an increased risk of moderate or severe pulmonary impairment [1]. Similarly, our study found TK, Cobb angle, and BMI to be statistically significant, albeit weak, predictors of percentage predicted FVC. The data suggest that thoracic hypokyphosis and larger curves contribute to pulmonary impairment in AIS patients. Previous literature demonstrates a larger degree of TK for overweight adolescents compared with normal to lowweight peers [5,6]. Our findings also identified this relationship. Xu et al. prospectively identified adolescents with normal kyphosis and compared pulmonary function testing with BMI [6]. Their findings identified more preserved pulmonary function in adolescents with a greater BMI, although the BMI threshold was set at >17.5, a value much lower than ours. Based on the results of our study, we believe that the larger value of TK observed in overweight patients with AIS might be protective of their pulmonary function. Older obese adults who have untreated AIS may not experience this as their obesity negatively affects their pulmonary function with advancing age [7]. Our findings indicate BMI and TK to be independently related to FVC. This is important as it continues to identify predictors of pulmonary function, which can be assessed or utilized in the management of AIS. Patients with a BMI >25 had a greater median TK and FVC than patients with BMI !25 (Table 2). This statistically significant difference suggests that preobese/obese children with AIS have better pulmonary function than their counterparts. Limitations to this study include its retrospective nature. Also, categories for overweight or normal weight were based off BMI cutoffs rather than weight for age percentiles provided by the CDC. This likely had less of an effect on analysis. Overall, our data confirm the hypothesis that heavier patients with AIS had more preserved TK, and as a possible result, more preserved pulmonary function. BMI and TK should be taken into consideration when counseling parents about the pulmonary aspects of AIS and the indications for intervention. For example, the indications and goals of
treatment for a child that is under- or normal weight with thoracic hypokyphosis and impaired pulmonary function, as defined by their FVC, might be different from those of a heavier child with preserved thoracic kyphosis and pulmonary function. Key points Thoracic kyphosis, BMI, and Cobb angle all contribute to the percentage predicted FVC of patients with AIS and structural main thoracic curves. Of all the variables tested, BMI and FVC had the strongest correlation, even more so than Cobb angle and FVC and TK and FVC. Heavier patients with AIS have greater degrees of TK and greater values of percentage predicted FVC.
Acknowledgments The authors acknowledge the contributions of Julia Leamon, MSN, RN, CPN, to this study. No financial support was received for the purposes of this study. References [1] Newton PO, Faro FD, Gollogly S, et al. Results of preoperative pulmonary function testing of adolescents with idiopathic scoliosis. J Bone Joint Surg Am 2005;87:1937e46. [2] Johnston CE, Richards BS, Sucato DJ, et al. Correlation of preoperative deformity magnitude and pulmonary function tests in adolescent idiopathic scoliosis. Spine 2011;36:1096e102. [3] Dreimann M, Hoffmann M, Kossow K, et al. Scoliosis and chest cage deformity measures predicting impairments in pulmonary function. Spine 2014;39:2024e33. [4] Smith AJ, O’Sullivan PB, Beales DJ, et al. Trajectories of childhood body mass index are associated with adolescent sagittal standing posture. Int J Pediatr Obes 2011;6:e97e106. [5] Li Y, Binkowski L, Grzywna A, et al. Is obesity in adolescent idiopathic scoliosis associated with larger curves and worse surgical outcomes? Spine (Phila Pa 1976) 2017;42:E156e62. [6] Xu L, Sun X, Zhu Z, et al. Body mass index as an indicator of pulmonary dysfunction in patients with adolescent idiopathic scoliosis. J Spinal Disord Tech 2015;28:226e31. [7] Jones RL, Nzekwu MM. The effects of body mass index on lung volumes. Chest 2006;130:827e33.
Do Heavier Patients With Adolescent Idiopathic Scoliosis Have More Preserved Thoracic Kyphosis and Pulmonary Function? Robert Tung, BSa, Mason Uvodich, BSa, John T. Anderson, MDb,*, Katie Carpenter, CPNP-PCb, Ashley Sherman, MAb, Rafael Lozano, MDc a
University of Kansas School of Medicine, 3901 Rainbow Blvd, Kansas City, KS 66160, USA b Children’s Mercy-Kansas City, 2401 Gillham Rd, Kansas City, MO 64108, USA c Department of Surgery, University of Nevada, Las Vegas, 4505 S. Maryland Pkwy, Las Vegas, NV 89154, USA Received 18 January 2018; revised 3 May 2018; accepted 5 May 2018
Abstract Study Design: Retrospective. Objectives: We aimed to determine if heavier patients with adolescent idiopathic scoliosis (AIS) had more preserved thoracic kyphosis (TK), and as a result, more preserved pulmonary function. Summary of Background Data: Some believe that childhood weight is predictive of adult sagittal plane parameters, with heavier children having greater TK as adults. Generally, thoracic scoliosis is coupled with loss of TK, which is associated with worsening pulmonary function. Methods: A total of 142 patients with AIS and a structural main thoracic curve were analyzed. We excluded patients with structural proximal thoracic curves (Lenke 2 and 4). Standing preoperative radiographs, pulmonary function tests, and preoperative body mass indices (BMIs) were reviewed. The main thoracic Cobb angle, T2eT12 TK, percentage predicted forced vital capacity (FVC) and BMI were recorded. Spearman correlation was determined. Linear regression analysis used FVC as the primary outcome and BMI, TK, and Cobb angle as the independent variables. BMI categories were overweight/obese (BMI >25) and normal (BMI !25). Wilcoxon rank-sum tests were performed to detect a difference in TK and BMI between the 2 groups. The Cobb angles between the two groups were analyzed by t tests. Results: Demonstrated correlations included BMI and FVC (0.37, p <.01), FVC and TK (0.26, p !.01), BMI and TK (0.23, p 5 .01), and FVC and Cobb angle (e0.23, p 5 .01). Linear regression revealed that Cobb angle (p <.01), TK (p !.01), and BMI (p !.01) remained statistically significant predictors of FVC. Wilcoxon rank-sum tests revealed a statistically significant difference between TK (p 5 .03) and FVC (p !.01) in the overweight/obese group and the normal group, with the overweight/obese group having greater values for both TK and FVC. The Cobb angles between the overweight/obese and normal group were not significantly different (p 5 .72). Conclusions: Heavier AIS patients have greater values of TK and percentage predicted FVC. Level of Evidence: Level III. Ó 2018 Scoliosis Research Society. All rights reserved. Keywords: AIS; Adolescent Idiopathic Scoliosis; Scoliosis; Obesity; Pulmonary function
Introduction Author disclosures: RT (none), MU (none), JTA (paid speaker at an American Academy of Pediatrics CME course), KC (none), AS (none), RL (none). Reviewed and approved by the Pediatric IRB at The Children’s Mercy Hospital & Clinics (IRB No. 16010073). No funding was received for the purpose of this study. *Corresponding author. Orthopaedic Surgery, University of MissouriKansas City School of Medicine, Children’s Mercy-Kansas City, 2408 Gillham Road, 2nd floor Annex, Kansas City, MO 64108, USA. Tel.: (816) 234-3075; fax: (816) 302-9743. E-mail address: [email protected] (J.T. Anderson).
Adolescent idiopathic scoliosis (AIS) is a threedimensional skeletal deformity of the spine affecting up to 3% of the population. Although typically benign, the natural progression of AIS may result in disturbances of body that affect morphology and physiology. AIS patients are at greatest risk of progression during the pubertal growth spurt. In general, thoracic scoliosis creates hypokyphosis. Studies have shown a correlation between thoracic
2212-134X/$ - see front matter Ó 2018 Scoliosis Research Society. All rights reserved. https://doi.org/10.1016/j.jspd.2018.05.007
R. Tung et al. / Spine Deformity 6 (2018) 704e706
hypokyphosis and worsening pulmonary function in children with AIS. Newton et al. described a positive association between thoracic kyphosis and forced vital capacity. Clinically relevant decreases in forced vital capacity are correlated with larger thoracic curves and with thoracic hypokyphosis [1-3]. The role of BMI in these patients is of importance because data suggest childhood obesity can affect adolescent spinal sagittal plane parameters [4]. Children with higher BMI will develop greater thoracic kyphosis compared to children with lower BMIs. In the senior author’s experience, children with AIS with normal to above normal thoracic kyphosis, have more persevered FVC% and higher BMIs than their hypokyphotic peers. This has implications when counseling parents about the pulmonary aspects of the disease and the indications for surgical intervention. Materials and Methods A retrospective Level III study of preoperative variables was conducted. These data included radiographs, pulmonary function testing (PFT) data, and BMI measurements of a consecutive series of AIS patients cared for by three different surgeons at a large tertiary children’s hospital from January 1, 2009, to January 1, 2016. Subjects included in this study were between ages 10 and 18 years and had a Cobb angle of greater than 50 degrees. All data were extracted from studies and measurements obtained during the preoperative visit. Patients with scoliosis not diagnosed as AIS or with underlying asthma or other known pulmonary disease, not directly attributed to their scoliosis, were excluded. Patients with a history of a previous thoracotomy or sternotomy; those who had an isolated thoracolumbar curve; those with a structural proximal thoracic curve; and patients with inadequate imaging, BMI, or PFT data were also excluded. Thoracic Cobb angle and the T2eT12 sagittal Cobb angle were measured using InteleViewer software. The percentage predicted FVC and BMI of each subject was obtained from the subject’s medical records. Spearman correlation was determined. Linear regression analysis was performed using FVC as the primary outcome and BMI, TK, and Cobb angle as the independent variables. BMI was dichotomized as overweight/obese (BMI>25) and normal (BMI !25). Wilcoxon rank-sum tests were performed to detect a difference in TK and FVC between the two groups. The Cobb angles between the two groups were analyzed by t tests. Alpha was set at 0.05 and power analysis was performed to a power of 0.80. Results Table 1 summarizes patient demographics. Our database generated 203 AIS patients that met our inclusion criteria. Of these patients, an additional 61 were excluded. The 142
705
Table 1 Patient demographics. 203 61 14 59.3 34.7 21.9 83.4
Total patients reviewed, N Patients excluded, mean Age (years), mean Thoracic Cobb angle (degrees), mean TK (degrees), mean BMI, mean %FVC, mean
BMI, body mass index; FVC, forced vital capacity; TK, thoracic kyphosis.
Table 2 Wilcoxon rank-sum for preobese/obese versus others. BMI >25 BMI !25
TK*, median (IQR)
FVCy, median (IQR)
39 (12) 33 (19)
91 (20) 80.6 (22.1)
BMI, body mass index; FVC, forced vital capacity; IQR, interquartile range; TK, thoracic kyphosis. * p 5 .03 for TK between the two groups. y p !.01 for FVC between the two groups.
AIS patients included for analysis had an average age of 14 years, Cobb angle of 59 , thoracic kyphosis of 35 , BMI of 21.9, and FVC% of 83. BMI, TK, and FVC were all positively correlated at a statistically significant level. A statistically significant negative correlation was found between FVC and Cobb angle (e0.23, p 5 .01). Of the variables, the strongest correlation was found between BMI and FVC (0.37, p<.01) followed by FVC and TK (0.26, p !.01) and FVC and Cobb angle (e0.23, p 5 .01). Linear regression revealed that Cobb angle (p<.01), TK (p !.01), and BMI (p !.01) all remained statistically significant predictors of FVC (R2 5 0.26). The coefficient of determination was e0.53 (95% confidence interval e0.76, e0.29) for Cobb angle, 1.04 for BMI (95% confidence interval 0.52, 1.55), and 0.31 for TK (95% confidence interval 0.16, 0.47). Wilcoxon rank-sum tests revealed a statistically significant difference between TK (p 5 .03) and FVC (p !.01) in the overweight/obese group (n 5 27) and the normal group (n 5 115), with the overweight/obese group having greater values for both TK and FVC (Table 2). The Cobb angles between the overweight/obese and normal groups were not significantly different (p 5 .72). Discussion We sought to identify associations between BMI and pulmonary function in adolescents with idiopathic scoliosis. Our major finding was that greater values of BMI and TK were correlated with better pulmonary function, as defined by a higher FVC. BMI and TK were correlated to a lower degree than their individual relationships to FVC. Also, they contributed independently to FVC percentage, with linear regression suggesting that the relationship of BMI to FVC may not be entirely mediated through TK.
706
R. Tung et al. / Spine Deformity 6 (2018) 704e706
The correlation between thoracic spinal deformity in AIS and decreased pulmonary function has been suggested in previous research. Newton et al. found the magnitude of the thoracic curve, number of vertebrae involved in the thoracic curve, thoracic hypokyphosis, and coronal imbalance to be associated with an increased risk of moderate or severe pulmonary impairment [1]. Similarly, our study found TK, Cobb angle, and BMI to be statistically significant, albeit weak, predictors of percentage predicted FVC. The data suggest that thoracic hypokyphosis and larger curves contribute to pulmonary impairment in AIS patients. Previous literature demonstrates a larger degree of TK for overweight adolescents compared with normal to lowweight peers [5,6]. Our findings also identified this relationship. Xu et al. prospectively identified adolescents with normal kyphosis and compared pulmonary function testing with BMI [6]. Their findings identified more preserved pulmonary function in adolescents with a greater BMI, although the BMI threshold was set at >17.5, a value much lower than ours. Based on the results of our study, we believe that the larger value of TK observed in overweight patients with AIS might be protective of their pulmonary function. Older obese adults who have untreated AIS may not experience this as their obesity negatively affects their pulmonary function with advancing age [7]. Our findings indicate BMI and TK to be independently related to FVC. This is important as it continues to identify predictors of pulmonary function, which can be assessed or utilized in the management of AIS. Patients with a BMI >25 had a greater median TK and FVC than patients with BMI !25 (Table 2). This statistically significant difference suggests that preobese/obese children with AIS have better pulmonary function than their counterparts. Limitations to this study include its retrospective nature. Also, categories for overweight or normal weight were based off BMI cutoffs rather than weight for age percentiles provided by the CDC. This likely had less of an effect on analysis. Overall, our data confirm the hypothesis that heavier patients with AIS had more preserved TK, and as a possible result, more preserved pulmonary function. BMI and TK should be taken into consideration when counseling parents about the pulmonary aspects of AIS and the indications for intervention. For example, the indications and goals of
treatment for a child that is under- or normal weight with thoracic hypokyphosis and impaired pulmonary function, as defined by their FVC, might be different from those of a heavier child with preserved thoracic kyphosis and pulmonary function. Key points Thoracic kyphosis, BMI, and Cobb angle all contribute to the percentage predicted FVC of patients with AIS and structural main thoracic curves. Of all the variables tested, BMI and FVC had the strongest correlation, even more so than Cobb angle and FVC and TK and FVC. Heavier patients with AIS have greater degrees of TK and greater values of percentage predicted FVC.
Acknowledgments The authors acknowledge the contributions of Julia Leamon, MSN, RN, CPN, to this study. No financial support was received for the purposes of this study. References [1] Newton PO, Faro FD, Gollogly S, et al. Results of preoperative pulmonary function testing of adolescents with idiopathic scoliosis. J Bone Joint Surg Am 2005;87:1937e46. [2] Johnston CE, Richards BS, Sucato DJ, et al. Correlation of preoperative deformity magnitude and pulmonary function tests in adolescent idiopathic scoliosis. Spine 2011;36:1096e102. [3] Dreimann M, Hoffmann M, Kossow K, et al. Scoliosis and chest cage deformity measures predicting impairments in pulmonary function. Spine 2014;39:2024e33. [4] Smith AJ, O’Sullivan PB, Beales DJ, et al. Trajectories of childhood body mass index are associated with adolescent sagittal standing posture. Int J Pediatr Obes 2011;6:e97e106. [5] Li Y, Binkowski L, Grzywna A, et al. Is obesity in adolescent idiopathic scoliosis associated with larger curves and worse surgical outcomes? Spine (Phila Pa 1976) 2017;42:E156e62. [6] Xu L, Sun X, Zhu Z, et al. Body mass index as an indicator of pulmonary dysfunction in patients with adolescent idiopathic scoliosis. J Spinal Disord Tech 2015;28:226e31. [7] Jones RL, Nzekwu MM. The effects of body mass index on lung volumes. Chest 2006;130:827e33.