Curve flexibility in adolescent idiopathic scoliosis (AIS) was one of the major concerns of spinal surgeons since the evolution of surgical correction techniques. In this respect, many tried to identify which criteria denote more rigid curve. In the present study, we aimed toward determining important factors influencing AIS curve flexibility on supine bending films. We assessed radiographs of 100 patients with AIS for direction of curves, number of involved vertebrae, apical vertebral translation and rotation, magnitude of main thoracic curve and T5-T12 kyphosis. Statistical analysis performed via stepwise linear regression model with these variables plus age and sex against flexibility index. According to regression analysis, there was a clear relationship between flexibility indexes (FI) and magnitude of main thoracic curve at all (P50) against rigid curves, apical vertebral rotation was a major determinant of curve flexibility also (P<0.001). Adolescent idiopathic scoliosis curves with larger Cobbâ��s angle and apical vertebral rotation show less flexibility on supine bending films. Â© 2015 Tehran University of Medical Sciences. All rights reserved

Ameri, E.

Behtash, H.

Daraie, A.

Mobini, B.

ACTA MEDICA IRANICA

English

Curve flexibility in adolescent idiopathic scoliosis (AIS) was one of the major concerns of spinal surgeons since the evolution of surgical correction techniques. In this respect, many tried to identify which criteria denote more rigid curve. In the present study, we aimed toward determining important factors influencing AIS curve flexibility on supine bending films. We assessed radiographs of 100 patients with AIS for direction of curves, number of involved vertebrae, apical vertebral translation and rotation, magnitude of main thoracic curve and T5-T12 kyphosis. Statistical analysis performed via stepwise linear regression model with these variables plus age and sex against flexibility index. According to regression analysis, there was a clear relationship between flexibility indexes (FI) and magnitude of main thoracic curve at all (P50%) against rigid curves, apical vertebral rotation was a major determinant of curve flexibility also (P<0.001). Adolescent idiopathic scoliosis curves with larger Cobb's angle and apical vertebral rotation show less flexibility on supine bending films

Ebrahim Ameri

Hamid Behtash

Bahram Mobini

Ariasb Daraie

Directory of Open Access Journals

 ORIGINAL ARTICLE   Corresponding Author: A. Daraie  Department of Spine Surgery, Shafa Yahyaeian Hospital, Iran University of Medical Sciences, Tehran, Iran  Tel: +98 21 33542000-8, Fax: +98 21 33542020, E-mail address: ariasb111@yahoo.com  Predictors of Curve Flexibility in Adolescent Idiopathic Scoliosis: a Retrospective Study of 100 Patients Ebrahim Ameri1, Hamid Behtash2, Bahram Mobini1,  and Ariasb Daraie1 1 Department of Spine Surgery, Shafa Yahyaeian Hospital, Iran University of Medical Sciences, Tehran, Iran 2 Department of Spine Surgery, Rasoole Akram Hospital, Iran University of Medical Sciences, Tehran, Iran 11 Received: 32 May. 2013; Accepted: 6 Jul. 2013  Abstract- Curve flexibility in adolescent idiopathic scoliosis (AIS) was one of the major concerns of spinal surgeons since the evolution of surgical correction techniques. In this respect, many tried to identify which criteria denote more rigid curve. In the present study, we aimed toward determining important factors influencing AIS curve flexibility on supine bending films. We assessed radiographs of 100 patients with AIS for direction of curves, number of involved vertebrae, apical vertebral translation and rotation, magnitude of main thoracic curve and T5-T12 kyphosis. Statistical analysis performed via stepwise linear regression model with these variables plus age and sex against flexibility index. According to regression analysis, there was a clear relationship between flexibility indexes (FI) and magnitude of main thoracic curve at all (P<0.001). When we consider flexible curves (FI>50%) against rigid curves, apical vertebral rotation was a major determinant of curve flexibility also (P<0.001). Adolescent idiopathic scoliosis curves with larger Cobb’s angle and apical vertebral rotation show less flexibility on supine bending films. © 2015 Tehran University of Medical Sciences. All rights reserved.  Acta Medica Iranica, 2015;53(3):182-185.   Keywords: Adolescent idiopathic scoliosis; Spinal flexibility; Supine bending films; Imaging   Introduction  Idiopathic scoliosis, a common entity has been the focus of attention since ancient times (1-2); there are many controversies to be elucidated. Since the past, one of major concerns for spine surgeons was determination of which curves could be considered flexible (3-9). These flexible curves have more opportunity to achieve full or near-full correction. But, with the advent of newer generations of spinal stabilization systems, this matter is of less importance but does not be pushed into a corner.                                                                                                              Radiographic analysis of scoliosis patients performs for multitude of reasons. Curve flexibility is one of the main determinants which surgeons take it into consideration for decision-making on which end-levels they could stop on (10,11). Despite availability of many imaging modalities to reveal the extent of flexibility of curves, none of them is completely flawless (6-9). Due to these reasons, many spine surgeons believe that no imaging modality could predict how much correction will be achieved during surgery (12). It is clear that more rigid curves need more intensive operations and may need inter-operative skeletal traction to achieve maximal correction, but in the presence of newer instruments, this is a matter of debate (13). We conduct this study in a retrospective fashion to establish which radiographic parameter could reliably predict curve flexibility.   Materials and Methods  We reviewed preoperative and postoperative radiographs of 100 patients (27 male, 73 female) with adolescent idiopathic scoliosis treated surgically by senior spinal surgeon of this article. Routine preoperative radiographs were standing anteroposteriorly and lateral views as well as supine bending views. Postoperative views were obtained standing AP and lateral projections. All patients underwent posterior segmented instrumented fusion some with and some without anterior release and fusion. Mean age of patients was 15.8 ± 2.3 years (from 12 to 24). Evaluated radiologic parameters are listed on E. Ameri, et al.     Acta Medica Iranica, Vol. 53, No. 3 (2015)    183 table1. Only single major curves included in this study. All parameters were analyzed by the same person. We assessed the magnitude of curves by Cobb’s method. Apical vertebral translation (AVT) defined as the distance from the center of apical vertebral body to center-sacral line (CSL) and expressed in centimeters. Apical vertebral rotation (AVR) evaluated by Perdriolle technique. Curve location defined according to the position of their apical vertebrae. We defined flexibility as a flexibility index (FI) of more than 50%. FI calculated through following equation:  (Cobb angle-bending Cobb angle)/Cobb angle  Subsequently, relationship of each parameter was analyzed with curve flexibility using stepwise linear regression model. Statistical analysis performed by SPSS-12 software.  Table 1. Radiologic parametersSD MEDIAN MODE MIN MAX MEAN VARIABLE 10.6 ١٠ ٣٠ ٢٢ ۵٣ 25.7 PT1 curve 22.7 ۶۵ ۵١٣٢ ١٠ ٠ 65.2 MT2 curve 13.7 ۴٨٠ ١٣ ٣٠ ٠ 39.5 TL/L3 curve 8.5 ۵/٢٩  ١ ٣١۵ ۵٢ 30.1 AVR4 5.8 ۶ ۶ ٢ ۵٩ 7.5 AVT5 1.4 ٠ ٢ ٢ ۵/۵  1.9 Displacement from CSL6 17.6 ۵/۴٢  ٢۵ ١٠٠ ١١ 43.8 FI7 19.5 ٨٠ ٠ ٣٠ ٣٠ 35.5 Kyphosis T5-T12 11.4 ۵/٧  ٠ ٠ ۵٠ 10.0 Postoperative PT curve 18.8 ٩٠ ٠ ٠ ٢٢ 25.4 Postoperative MT curve 12.3 ٠ ٠ ١٣ ۵٠ 14.1 Postoperative TL/L curve 11.2 ٣٠ ٣٠ ۵ ۶۵ 30.0 Postoperative kyphosis T5-T12  1. proximal thoracic   2. main thoracic   3. thoracolumbar/lumbar 4. apical vertebral rotation   5. apical vertebral translation 6. Center sacral line 7. flexibility index  Results  One hundred radiographs of adolescent idiopathic scoliosis patients were evaluated. Median age of patients at the time of surgery was 15.8 ± 2.3 (range: 12-24 years). Of these patients, 73 of them were female and remaining (27patients) were male. Ninety percent of curves (90 cases) faced toward right. With respect to radiologic parameters, the mean magnitude of main thoracic curves was 65.2 ± 22.7 degrees. Mean value for apical vertebral rotation (AVR) and apical vertebral translation (AVT) were 30.1 ± 8.5 and 7.5 ± 5.8 degrees, respectively. Coronal decompensation which defined as displacement from center-sacral line (CSL) was 1.9 cm on average (SD=1.4 cm). Average number of involved vertebrae was 7.9 ± 1.6 (ranged from 5 to 14). Mean flexibility index (FI) was 43.8% (SD=17.6). All patients underwent posterior instrumented spinal fusion using multi-segmented hook and rod systems. We entered some variables including age, sex, direction of main thoracic curve, coronal decompensation, AVR, AVT, magnitude of main thoracic curve, number of involved vertebrae and preoperative T5-T12 kyphosis in stepwise generalized linear regression analysis. Of these variables, no significant correlation was found between flexibility index and these variables except magnitude of main thoracic curve and (P<0.001). These results are summarized in table 2.   Table 2. Significance of main thoracic curve in flexibility  B SE of B Standardized β t P-value 95% CI for B Main thoracic curve -0.441 0.069 -0.556 -6.417 >0.001 (-0.578) - (-0.305) Constant  72.123 4.743 -- 15.205 >0.001 62.703 – 81.544  In the next step, we divide patients into two groups; patients with FI equal or more than 50% and patients with less than 50% flexibility and reassess above mentioned variables respect to this cut-off point and then compare these two groups. As shown on table 3, there is an inverse relationship between flexible curves (which is defined as FI more than 50%) and AVR (adjusted R2=0.201).     Also, in Pearson relation coefficient analysis, we found a strong linear relationship between magnitudes of preoperative proximal thoracic, main thoracic, thoracolumbar/lumbar curves and their postoperative values (P<0.001). These relationships are shown in the table 4.  Predictors of curve flexibility in AIS 184    Acta Medica Iranica, Vol. 53, No. 3 (2015)    Table 3. Relationship of AVR* with flexibility  B SE of B Standardized β t P-value 95% CI for B Apical vertebral rotation 0.025 0.005 0.458 4.935 >0.001 0.015-0.035 Constant  0.904 0.161 -- 5.599 >0.001 0.583-1.224 *AVR: apical vertebral rotation  Table 4. Pearson relation coefficients for preoperative and postoperative values r P-value  0.761 <0.001 Proximal thoracic curve 0.735 <0.001 Main thoracic curve 0.596 <0.001 Thoracolumbar / lumbar curve  Discussion  Since evolution of surgical techniques for correction of idiopathic scoliosis, flexibility of scoliotic curves was a major concern of spinal surgeons (3-9). Several studies were conducted to determine the threshold of structurality, determinants of curve flexibility, fusion levels and corrective strategy (3-19). Despite introduction of many ways to demonstrate maximal curve flexibility, supine bending radiographs are still the mainstay of preoperative planning (9,12,16,17). In this study, when considering all variables relative to flexibility index, we found a strong correlation between the magnitude of main thoracic curve and flexibility of them (adjusted R2=0.302, P<0.001). When we analyzed flexible curve against rigid ones with the same parameters, the most statistically significant factor was AVR (P<0.001). FI was inversely proportional to AVR (adjusted R2=0.201). Age is a known factor affecting curve flexibility in a relatively linear fashion. In the present study, age did not achieve significance, although we should remember that ages of our patients, at their extremes, were just slightly more than one decade different. Thus jumping into conclusion for age influence according to these results may be unwise. In the literature, gender is discussed under the topic of curve progression determinants and less as a factor influencing curve flexibility. In this analysis, gender did not meet statistical significance respect to FI. Translatory shift of the entire spine is more dependent on the presence of curves at extremes of the spine (i.e. cervicothoracic and lumbosacral regions), where there is no room for compensation. Therefore, a large AVT may be representative of a large curve below MT curve. So, inclusion of this parameter may lead to bias in our opinion. Therefore, we consider AVT rather than the total coronal decompensation. Although in this respect, AVT did not achieve significance. Adolescent idiopathic scoliotic curves are usually facing toward right. Leftward curves, especially if painful, raise the possibility of the presence of an intra-spinal pathology, but in our review, we did not encounter any evidence about relationship of direction and flexibility of curves. To disclose this relationship, we performed statistical analysis and did not find any correlation between the direction of MT curves and their flexibility. Curves with larger Cobb’s angle are expected to have more AVR and AVT. Despite gaining significance by MT curves, but AVR and AVT were not major determinants of FI in supine bending films.  In this study, there was no relationship between sagittal alignment (T5-T12 kyphosis) and FI. Analysis of the relationship between sagittal alignment and flexibility of scoliotic curves in the coronal plane is complicated. In lower Cobb angles, the difference between apparent sagittal alignments (as seen on routine lateral films) and true sagittal alignment (as seen on stagnant view) is negligible. But in larger ones, this difference gain significance. So, correlating such sagittal profile with flexibility in the coronal plane is somewhat difficult. In summary, the major determinant of curve flexibility in adolescent idiopathic scoliosis is magnitude of main thoracic curve at all, but when comparing flexible curves versus rigid ones AVR becomes more impressive in an inverse fashion.  References  1. Kim HJ, Blanco JS, Widmann RF. Update on the management of idiopathic scoliosis. Curr Opin Pediatr 2009;21(1):55-64. E. Ameri, et al.     Acta Medica Iranica, Vol. 53, No. 3 (2015)    185 2. Weinstein SL. Natural History. Spine 1999;24(24):2592-600. 3. Sun YQ, Samartizis D, Cheung KM, et al. The "X-Factor" index: a new parameter for the assessment of adolescent idiopathic scoliosis correction. Eur Spine J 2011;20(1):144-50. 4. Hamzaoglu A, Talu U, Tezer M, et al. Assessment of Curve Flexibility in Adolescent Idiopathic Scoliosis. Spine 2005;30(14):1637-42. 5. Clamp JA, Anderws JR, Grevitt MP. A study of the radiologic predictor of curve flexibility in adolescent idiopathic scoliosis. J Spinal Disord Tech 2008;21(3):213-5.  6. Hasler CC, Hefti F, Buchler P. Coronal plane segmental flexibility in thoracic adolescent idiopathic scoliosis assessed by fulcrum-bending radiographs. Eur Spine J 2010;19(5):732-8. 7. Lamarre ME, Parent S, Labelle H, et al. Assessment of Spinal Flexibility in Adolescent Idiopathic Scoliosis. Suspension versus Side-Bending Radiography. Spine 2009;34(6):591-7. 8. Davis BJ, Gadgil A, Trivedi J, et al. Traction Radiography Performed under General Anesthetic: A New Technique for Assessing Idiopathic Scoliosis Curves. Spine 2004;29(21):2466-70. 9. Watanabe K, Kawakami N, Nishiwaki Y, et al. Traction Versus Supine Side-bending Radiographs in Determining Flexibility, What Factors Influence These Techniques? Spine 2007;32(23):2604-9. 10. King HA, Moe JH, Bradford DS, et al. The selection of fusion levels in thoracic idiopathic scoliosis. J Bone Joint Surg Am 1983;65(9):1302-13. 11. Knapp DR Jr, Price CT, Jones ET, et al. Choosing fusion levels in progressive thoracic idiopathic scoliosis. Spine 1992;17(10):1159-65. 12. Aronsson DD, Stokes IA, Ronchetti PJ, et al. Surgical correction of vertebral axial rotation in adolescent idiopathic scoliosis: prediction by lateral bending films. J Spinal Disord 1996;9(3):214-9. 13. Luhmann SJ, Lenke LG, Kim YJ, et al. Thoracic Adolescent Idiopathic Scoliosis Curves Between 70 degrees and 100 degrees: Is Anterior Release Necessary? Spine 2005;30(18):2061-7. 14. Luk KD, Cheung WY, Wong Y, et al. The predictive value of the fulcrum bending radiograph in spontaneous apical vertebral derotation in adolescent idiopathic scoliosis. Spine 2012;37(15):E922-6. 15. Cheung WY, Lenke LG, Luk KD. Prediction of scoliosis correction with thoracic segmental pedicle screw constructs using fulcrum bending radiogeaphs. Spine 2010;35(5):557-61. 16. Li J, Dumonski ML, Samartzis D, et al. Coronal deformity correction in adolescent idiopathic scoliosis patients using the fulcrum – bending radiograph:a prospective comparative analysis of the proximal thoracic, main thoracic, and thoracolumbar/lumbar curves. Eur Spine J 2011;20(1):105-11. 17. Liu RW, Teng AL, Armstrong DG. Comparison of supine bending,Push-Prone, and traction under general anesthesia radiographs in correction in adolescent idiopathic scoliosis. Spine 2010;35(4):416-22. 18. Chen ZQ, Zhao YF, Bai YS, et al. Factors affecting curve flexibility skeletally immature and mature idiopathic scoliosis. J Orthop Sci 2011;16(2):133-8. 19. Ameri E, Behtash H, Mobini B, et al. Radiographic outcome of surgical treatment of adolescent idiopathic scoliosis in males versus females. Scoliosis 2008;3(1):12.  

Predictors of Curve Flexibility in Adolescent Idiopathic Scoliosis: a Retrospective Study of 100 Patients

eprints Iran University of Medical Sciences

 ORIGINAL ARTICLE   Corresponding Author: A. Daraie  Department of Spine Surgery, Shafa Yahyaeian Hospital, Iran University of Medical Sciences, Tehran, Iran  Tel: +98 21 33542000-8, Fax: +98 21 33542020, E-mail address: ariasb111@yahoo.com  Predictors of Curve Flexibility in Adolescent Idiopathic Scoliosis: a Retrospective Study of 100 Patients Ebrahim Ameri1, Hamid Behtash2, Bahram Mobini1,  and Ariasb Daraie1 1 Department of Spine Surgery, Shafa Yahyaeian Hospital, Iran University of Medical Sciences, Tehran, Iran 2 Department of Spine Surgery, Rasoole Akram Hospital, Iran University of Medical Sciences, Tehran, Iran 11 Received: 32 May. 2013; Accepted: 6 Jul. 2013  Abstract- Curve flexibility in adolescent idiopathic scoliosis (AIS) was one of the major concerns of spinal surgeons since the evolution of surgical correction techniques. In this respect, many tried to identify which criteria denote more rigid curve. In the present study, we aimed toward determining important factors influencing AIS curve flexibility on supine bending films. We assessed radiographs of 100 patients with AIS for direction of curves, number of involved vertebrae, apical vertebral translation and rotation, magnitude of main thoracic curve and T5-T12 kyphosis. Statistical analysis performed via stepwise linear regression model with these variables plus age and sex against flexibility index. According to regression analysis, there was a clear relationship between flexibility indexes (FI) and magnitude of main thoracic curve at all (P<0.001). When we consider flexible curves (FI>50%) against rigid curves, apical vertebral rotation was a major determinant of curve flexibility also (P<0.001). Adolescent idiopathic scoliosis curves with larger Cobb’s angle and apical vertebral rotation show less flexibility on supine bending films. © 2015 Tehran University of Medical Sciences. All rights reserved.  Acta Medica Iranica, 2015;53(3):182-185.   Keywords: Adolescent idiopathic scoliosis; Spinal flexibility; Supine bending films; Imaging   Introduction  Idiopathic scoliosis, a common entity has been the focus of attention since ancient times (1-2); there are many controversies to be elucidated. Since the past, one of major concerns for spine surgeons was determination of which curves could be considered flexible (3-9). These flexible curves have more opportunity to achieve full or near-full correction. But, with the advent of newer generations of spinal stabilization systems, this matter is of less importance but does not be pushed into a corner.                                                                                                              Radiographic analysis of scoliosis patients performs for multitude of reasons. Curve flexibility is one of the main determinants which surgeons take it into consideration for decision-making on which end-levels they could stop on (10,11). Despite availability of many imaging modalities to reveal the extent of flexibility of curves, none of them is completely flawless (6-9). Due to these reasons, many spine surgeons believe that no imaging modality could predict how much correction will be achieved during surgery (12). It is clear that more rigid curves need more intensive operations and may need inter-operative skeletal traction to achieve maximal correction, but in the presence of newer instruments, this is a matter of debate (13). We conduct this study in a retrospective fashion to establish which radiographic parameter could reliably predict curve flexibility.   Materials and Methods  We reviewed preoperative and postoperative radiographs of 100 patients (27 male, 73 female) with adolescent idiopathic scoliosis treated surgically by senior spinal surgeon of this article. Routine preoperative radiographs were standing anteroposteriorly and lateral views as well as supine bending views. Postoperative views were obtained standing AP and lateral projections. All patients underwent posterior segmented instrumented fusion some with and some without anterior release and fusion. Mean age of patients was 15.8 ± 2.3 years (from 12 to 24). Evaluated radiologic parameters are listed on E. Ameri, et al.     Acta Medica Iranica, Vol. 53, No. 3 (2015)    183 table1. Only single major curves included in this study. All parameters were analyzed by the same person. We assessed the magnitude of curves by Cobb’s method. Apical vertebral translation (AVT) defined as the distance from the center of apical vertebral body to center-sacral line (CSL) and expressed in centimeters. Apical vertebral rotation (AVR) evaluated by Perdriolle technique. Curve location defined according to the position of their apical vertebrae. We defined flexibility as a flexibility index (FI) of more than 50%. FI calculated through following equation:  (Cobb angle-bending Cobb angle)/Cobb angle  Subsequently, relationship of each parameter was analyzed with curve flexibility using stepwise linear regression model. Statistical analysis performed by SPSS-12 software.  Table 1. Radiologic parametersSD MEDIAN MODE MIN MAX MEAN VARIABLE 10.6 ٢٢ ٣٠ ١٠ ۵٣ 25.7 PT1 curve 22.7 ۶۵ ۵٠ ١٠ ١٣٢ 65.2 MT2 curve 13.7 ۴٠ ٣٠ ١٣ ٨٠ 39.5 TL/L3 curve 8.5 ۵/٢٩  ٣١ ١۵ ۵٢ 30.1 AVR4 5.8 ۶ ۶ ٢ ۵٩ 7.5 AVT5 1.4 ٢ ٢ ٠ ۵/۵  1.9 Displacement from CSL6 17.6 ۵/۴٢  ٢۵ ١١ ١٠٠ 43.8 FI7 19.5 ٣٠ ٣٠ ٠ ٨٠ 35.5 Kyphosis T5-T12 11.4 ۵/٧  ٠ ٠ ۵٠ 10.0 Postoperative PT curve 18.8 ٢٢ ٠ ٠ ٩٠ 25.4 Postoperative MT curve 12.3 ١٣ ٠ ٠ ۵٠ 14.1 Postoperative TL/L curve 11.2 ٣٠ ٣٠ ۵ ۶۵ 30.0 Postoperative kyphosis T5-T12  1. proximal thoracic   2. main thoracic   3. thoracolumbar/lumbar 4. apical vertebral rotation   5. apical vertebral translation 6. Center sacral line 7. flexibility index  Results  One hundred radiographs of adolescent idiopathic scoliosis patients were evaluated. Median age of patients at the time of surgery was 15.8 ± 2.3 (range: 12-24 years). Of these patients, 73 of them were female and remaining (27patients) were male. Ninety percent of curves (90 cases) faced toward right. With respect to radiologic parameters, the mean magnitude of main thoracic curves was 65.2 ± 22.7 degrees. Mean value for apical vertebral rotation (AVR) and apical vertebral translation (AVT) were 30.1 ± 8.5 and 7.5 ± 5.8 degrees, respectively. Coronal decompensation which defined as displacement from center-sacral line (CSL) was 1.9 cm on average (SD=1.4 cm). Average number of involved vertebrae was 7.9 ± 1.6 (ranged from 5 to 14). Mean flexibility index (FI) was 43.8% (SD=17.6). All patients underwent posterior instrumented spinal fusion using multi-segmented hook and rod systems. We entered some variables including age, sex, direction of main thoracic curve, coronal decompensation, AVR, AVT, magnitude of main thoracic curve, number of involved vertebrae and preoperative T5-T12 kyphosis in stepwise generalized linear regression analysis. Of these variables, no significant correlation was found between flexibility index and these variables except magnitude of main thoracic curve and (P<0.001). These results are summarized in table 2.   Table 2. Significance of main thoracic curve in flexibility  B SE of B Standardized β t P-value 95% CI for B Main thoracic curve -0.441 0.069 -0.556 -6.417 >0.001 (-0.578) - (-0.305) Constant  72.123 4.743 -- 15.205 >0.001 62.703 – 81.544  In the next step, we divide patients into two groups; patients with FI equal or more than 50% and patients with less than 50% flexibility and reassess above mentioned variables respect to this cut-off point and then compare these two groups. As shown on table 3, there is an inverse relationship between flexible curves (which is defined as FI more than 50%) and AVR (adjusted R2=0.201).     Also, in Pearson relation coefficient analysis, we found a strong linear relationship between magnitudes of preoperative proximal thoracic, main thoracic, thoracolumbar/lumbar curves and their postoperative values (P<0.001). These relationships are shown in the table 4.  Predictors of curve flexibility in AIS 184    Acta Medica Iranica, Vol. 53, No. 3 (2015)    Table 3. Relationship of AVR* with flexibility  B SE of B Standardized β t P-value 95% CI for B Apical vertebral rotation 0.025 0.005 0.458 4.935 >0.001 0.015-0.035 Constant  0.904 0.161 -- 5.599 >0.001 0.583-1.224 *AVR: apical vertebral rotation  Table 4. Pearson relation coefficients for preoperative and postoperative values r P-value  0.761 <0.001 Proximal thoracic curve 0.735 <0.001 Main thoracic curve 0.596 <0.001 Thoracolumbar / lumbar curve  Discussion  Since evolution of surgical techniques for correction of idiopathic scoliosis, flexibility of scoliotic curves was a major concern of spinal surgeons (3-9). Several studies were conducted to determine the threshold of structurality, determinants of curve flexibility, fusion levels and corrective strategy (3-19). Despite introduction of many ways to demonstrate maximal curve flexibility, supine bending radiographs are still the mainstay of preoperative planning (9,12,16,17). In this study, when considering all variables relative to flexibility index, we found a strong correlation between the magnitude of main thoracic curve and flexibility of them (adjusted R2=0.302, P<0.001). When we analyzed flexible curve against rigid ones with the same parameters, the most statistically significant factor was AVR (P<0.001). FI was inversely proportional to AVR (adjusted R2=0.201). Age is a known factor affecting curve flexibility in a relatively linear fashion. In the present study, age did not achieve significance, although we should remember that ages of our patients, at their extremes, were just slightly more than one decade different. Thus jumping into conclusion for age influence according to these results may be unwise. In the literature, gender is discussed under the topic of curve progression determinants and less as a factor influencing curve flexibility. In this analysis, gender did not meet statistical significance respect to FI. Translatory shift of the entire spine is more dependent on the presence of curves at extremes of the spine (i.e. cervicothoracic and lumbosacral regions), where there is no room for compensation. Therefore, a large AVT may be representative of a large curve below MT curve. So, inclusion of this parameter may lead to bias in our opinion. Therefore, we consider AVT rather than the total coronal decompensation. Although in this respect, AVT did not achieve significance. Adolescent idiopathic scoliotic curves are usually facing toward right. Leftward curves, especially if painful, raise the possibility of the presence of an intra-spinal pathology, but in our review, we did not encounter any evidence about relationship of direction and flexibility of curves. To disclose this relationship, we performed statistical analysis and did not find any correlation between the direction of MT curves and their flexibility. Curves with larger Cobb’s angle are expected to have more AVR and AVT. Despite gaining significance by MT curves, but AVR and AVT were not major determinants of FI in supine bending films.  In this study, there was no relationship between sagittal alignment (T5-T12 kyphosis) and FI. Analysis of the relationship between sagittal alignment and flexibility of scoliotic curves in the coronal plane is complicated. In lower Cobb angles, the difference between apparent sagittal alignments (as seen on routine lateral films) and true sagittal alignment (as seen on stagnant view) is negligible. But in larger ones, this difference gain significance. So, correlating such sagittal profile with flexibility in the coronal plane is somewhat difficult. In summary, the major determinant of curve flexibility in adolescent idiopathic scoliosis is magnitude of main thoracic curve at all, but when comparing flexible curves versus rigid ones AVR becomes more impressive in an inverse fashion.  References  1. Kim HJ, Blanco JS, Widmann RF. Update on the management of idiopathic scoliosis. Curr Opin Pediatr 2009;21(1):55-64. E. Ameri, et al.     Acta Medica Iranica, Vol. 53, No. 3 (2015)    185 2. Weinstein SL. Natural History. Spine 1999;24(24):2592-600. 3. Sun YQ, Samartizis D, Cheung KM, et al. The "X-Factor" index: a new parameter for the assessment of adolescent idiopathic scoliosis correction. Eur Spine J 2011;20(1):144-50. 4. Hamzaoglu A, Talu U, Tezer M, et al. Assessment of Curve Flexibility in Adolescent Idiopathic Scoliosis. Spine 2005;30(14):1637-42. 5. Clamp JA, Anderws JR, Grevitt MP. A study of the radiologic predictor of curve flexibility in adolescent idiopathic scoliosis. J Spinal Disord Tech 2008;21(3):213-5.  6. Hasler CC, Hefti F, Buchler P. Coronal plane segmental flexibility in thoracic adolescent idiopathic scoliosis assessed by fulcrum-bending radiographs. Eur Spine J 2010;19(5):732-8. 7. Lamarre ME, Parent S, Labelle H, et al. Assessment of Spinal Flexibility in Adolescent Idiopathic Scoliosis. Suspension versus Side-Bending Radiography. Spine 2009;34(6):591-7. 8. Davis BJ, Gadgil A, Trivedi J, et al. Traction Radiography Performed under General Anesthetic: A New Technique for Assessing Idiopathic Scoliosis Curves. Spine 2004;29(21):2466-70. 9. Watanabe K, Kawakami N, Nishiwaki Y, et al. Traction Versus Supine Side-bending Radiographs in Determining Flexibility, What Factors Influence These Techniques? Spine 2007;32(23):2604-9. 10. King HA, Moe JH, Bradford DS, et al. The selection of fusion levels in thoracic idiopathic scoliosis. J Bone Joint Surg Am 1983;65(9):1302-13. 11. Knapp DR Jr, Price CT, Jones ET, et al. Choosing fusion levels in progressive thoracic idiopathic scoliosis. Spine 1992;17(10):1159-65. 12. Aronsson DD, Stokes IA, Ronchetti PJ, et al. Surgical correction of vertebral axial rotation in adolescent idiopathic scoliosis: prediction by lateral bending films. J Spinal Disord 1996;9(3):214-9. 13. Luhmann SJ, Lenke LG, Kim YJ, et al. Thoracic Adolescent Idiopathic Scoliosis Curves Between 70 degrees and 100 degrees: Is Anterior Release Necessary? Spine 2005;30(18):2061-7. 14. Luk KD, Cheung WY, Wong Y, et al. The predictive value of the fulcrum bending radiograph in spontaneous apical vertebral derotation in adolescent idiopathic scoliosis. Spine 2012;37(15):E922-6. 15. Cheung WY, Lenke LG, Luk KD. Prediction of scoliosis correction with thoracic segmental pedicle screw constructs using fulcrum bending radiogeaphs. 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Predictors of curve flexibility in adolescent idiopathic scoliosis: A retrospective study of 100 patients

http://eprints.iums.ac.ir/5086/1/Predictors%20of%20curve%20flexibility%20in%20adolescent%20idiopathic%20scoliosis%20A%20retrospective%20study%20of%20100%20patients.pdf

Predictors of curve flexibility in adolescent idiopathic scoliosis: A retrospective study of 100 patients

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