What is the optimal cutoff value of the axis-line-angle technique for evaluating trunk imbalance in coronal plane?

Accepted Manuscript Title: What is the optimal cut-off value of the axis-line-angle technique for evaluating trunk imbalance in coronal plane? Author: Rui-Fang Zhang, Yu-Chuan Fu, Yi Lu, Xiao-Xia Zhang, Yu-Min Hu, Yong-Jin Zhou, Nai-Feng Tian, Jia-Wei He, Zhi-Han Yan PII: DOI: Reference:

S1529-9430(16)30962-7 http://dx.doi.org/doi: 10.1016/j.spinee.2016.09.012 SPINEE 57161

To appear in:

The Spine Journal

Received date: Revised date: Accepted date:

30-3-2016 28-7-2016 14-9-2016

Please cite this article as: Rui-Fang Zhang, Yu-Chuan Fu, Yi Lu, Xiao-Xia Zhang, Yu-Min Hu, Yong-Jin Zhou, Nai-Feng Tian, Jia-Wei He, Zhi-Han Yan, What is the optimal cut-off value of the axis-line-angle technique for evaluating trunk imbalance in coronal plane?, The Spine Journal (2016), http://dx.doi.org/doi: 10.1016/j.spinee.2016.09.012. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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What is the optimal cut-off value of the axis-line-angle

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technique for evaluating trunk imbalance in coronal plane?

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Authors: Rui-Fang Zhang, MDa,c, Yu-Chuan Fu, MDb,c, Yi Lu, MDb, Xiao-Xia Zhang,

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MDb, Yu-Min Hu, MDb, Yong-Jin Zhou, MDb, Nai-Feng Tian, MDd, Jia-Wei He, MDb,

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Zhi-Han Yan, MDb

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c

Rui-Fang Zhang and Yu-Chuan Fu contributed equally to this study.

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Affiliations and Addresses:

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a

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Medicine, 3333 Binsheng Road, 310052, Hangzhou, China.

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b

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University, 109 Xueyuanxi Road, 325027, Wenzhou, China.

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d

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University, 109 Xueyuanxi Road, 325027, Wenzhou, China.

Departments of Radiology, Children’s Hospital of Zhejiang University School of

Departments of Radiology, The Second Affiliated Hospital of Wenzhou Medical

Departments of Spine Surgery, The Second Affiliated Hospital of Wenzhou Medical

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Corresponding Author:

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Zhi-Han Yan, MD

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Department of Radiology

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The Second Affiliated Hospital of Wenzhou Medical University

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109 Xueyuanxi Road

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325027 Wenzhou

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China

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Tel: 86-13567709801

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Fax: 86-577-88832693

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[email protected]

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Acknowledgment

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The authors contracted with SCINET Co., Ltd, Beijing, China, to edit our manuscript. We thank

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for their excellent services. We maintained complete control over the direction and content of the

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manuscript.

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Abstract

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BACKGROUND CONTEXT: Accurately evaluating the extent of trunk imbalance

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in the coronal plane is significant for patients before and after treatment. We

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preliminarily practiced a new method, axis-line-angle technique (ALAT), for

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evaluating coronal trunk imbalance with excellent intrao-bserver and inter-observer

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reliability. Radiologists and surgeons were encouraged to use this method in clinic.

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However, the optimal cut-off value of ALAT, determined the extent of coronal trunk

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imbalance, has not been calculated up to now.

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PURPOSE: The purpose of this study was to identify the cut-off value of ALAT that

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best predicts a positive measurement point to assess coronal balance/imbalance.

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STUDY DESIGN/SETTING: A retrospective study at a university affiliated hospital.

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PATIENT SAMPLE: A total of 130 patients with C7-CSVL > 0 mm and age 10–18

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years were recruited in this study from September 2013 to December 2014.

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OUTCOME MEASURES: Data were analyzed to determine the optimal cut-off

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value of ALAT measurement.

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METHODS: The C7-CSVL and ALAT measurement were conducted respectively

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twice on plain film within a two-week interval by two radiologists. The optimal

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cut-off value of ALAT was analyzed via receiver operator characteristic (ROC) curve.

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Comparison variables were performed with chi-square test between the C7-CSVL and

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ALAT measurement for evaluating trunk imbalance. Kappa (κ) agreement coefficient

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method was used to test the intra-observer and inter-observer agreement of C7-CSVL

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and ALAT. This study was funded by the Wenzhou Science and Technology Bureau in

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China (Y20070019; about $2,000), and the funder did not have any influence on the

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course of the study.

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RESULTS: The ROC curve area for the ALAT was 0.82 (95% confidence interval

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(CI): 0.753 – 0.894, P < 0.001). The maximum Youden index (YI) was 0.51 and the

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corresponding cut-off point was 2.59°. No statistical difference was found between

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C7-CSVL and ALAT measurement for evaluating trunk imbalance (P﹥0.05).

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Intra-observer agreement values for the C7-CSVL measurements by observers 1 and 2

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were 0.79 and 0.91 (P < 0.001), respectively. And intra-observer agreement values for

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the ALAT measurements were both 0.89 by observers 1 and 2 (P < 0.001). The

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inter-observer agreement values for the first and second measurements with C7-CSVL

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were 0.78 and 0.85 (P < 0.001), respectively. And the inter-observer agreement values

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for the first and second measurements with ALAT were 0.91 and 0.88 (P < 0.001),

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respectively.

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CONCLUSIONS: The newly developed ALAT provided an acceptable optimal

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cut-off value for evaluating trunk imbalance in the coronal plane with a high level of

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intra-observer and inter-observer agreement, which suggesting that the ALAT is

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suitable for clinical use.

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Keywords: coronal balance; inter-observer agreement; central sacral vertical line;

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radiography.

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Introduction

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Normally the trunk is straight when viewed from behind, a plumb line dropped from

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the C7 spinous process to the gluteal fold is perpendicular to the ground. Otherwise,

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trunk imbalance occured caused by spinal curvature, pelvic obliquity, leg length

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discrepancy and others. The Scoliosis Research Society (SRS) [1] defined trunk

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imbalance in terms of the distance from the cephalad endpoints (T1, C7 or the inion)

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to the vertical line passing through S1 in the coronal plane. King et al. [2] described

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the central sacral line (CSL), a line from the center of the sacrum perpendicular to the

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horizontal line connecting the bilateral iliac crests. However, the sacrum, which

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determines position of the CSL, is not always horizontal. Therefore, Lenke et al. [3]

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modified the CSL concept and proposed the central sacral vertical line (CSVL), a line

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from the midpoint of S1 parallel to the edge of the radiograph. Therefore, the most

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widely practice for evaluating trunk imbalance in the coronal plane is measurement of

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the distance from the C7 plumb line (C7PL) to the central sacral vertical line (CSVL)

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(C7-CSVL), for which the normal range is 0 mm – 20 mm [4-8].

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However, there was a significant intra-observer difference in experiments of

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evaluating repeated the drawing of the CSVL [9]. Also there was high intra-observer

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variability in surgeons regarding positioning of the CSVL in clinical settings [10]. In

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some conditions, the intestinal contents can obscure the sacral vertebra, especially the

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superior border of S1 inevitably [11-13]. Based on advancements in digital imaging

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technology and our accumulated clinical experience, we preliminarily developed the

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axis-line-angle technique (ALAT), a new method of evaluating trunk imbalance in the

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coronal plane [13]. We have demonstrated that the ALAT has precise measurement

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points, a simple measurement procedure, and good reliability. However, the cut-off

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value of ALAT, which is crucial for evaluating trunk imbalance accurately and

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effectively, has not been established. Therefore, in this study，we further identified the

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cut-off value of the ALAT measurement that best predicts a positive measurement

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point in the coronal plane.

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Materials and Methods

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Study Subjects

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Approval of the ethical review board was obtained prior to the study (approval

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number: 8657788002560).130 patients aged from 10 to 18 years and had a C7-CSVL

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measurement greater than 0 mm were recruited for this study, between September

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2013 and December 2014. Exclusion criteria included trunk imbalance secondary to

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spine surgery, pelvic rotation, tumors, neuromuscular diseases, full-leg length

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discrepancy and osteoarthritis.

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Imaging equipment

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Computed radiography for full spine anteroposterior radiographs was performed as

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previously described [12], with Siemens Multix TOP computed radiography system

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(Siemens, Shanghai, China) and Picture Archiving and Communication System

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(PACS) v. 3.0 (Infinitt, Shanghai, China).

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Radiographic evaluation

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Standing anteroposterior X-ray films were taken before treatment. C7-CSVL and

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ALAT were respectively used in the assessment of 130 whole-spine standing

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anteroposterior radiographs twice by two radiologists, with an interval of two weeks

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to minimize memory effects. C7-CSVL was measured as the deviation of the CSVL

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from the C7 plumb line (Fig. 1), whereas ALAT was measured as the angle between

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the line connecting the centroid of C7 to the midpoint of the superior margin of the

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symphysis pubis and the C7 plumb line [13] (Fig. 2). The vertebral centroid of C7 was

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defined as the center created by two oblique lines connecting the contralateral corners

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of C7 [14].

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Statistical Analysis

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The Kolmogorov-Smirnov (K-S) test for normality was applied for all variables.

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Descriptive statistics (mean and range) were used to report radiological measurements.

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The predictive strength was assessed by using the area under the receiver operating

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characteristic curve (AUC) values. The AUC coefficients ranged from 0 to 1, where 1

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indicated perfect sensitivity and specificity [15]. The result with the highest Youden

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index (YI) in the ROC curve analysis was defined as the optimal cut-off point.

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Comparison variables were performed using chi-square test between the C7-CSVL

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and ALAT measurement for evaluating trunk imbalance. Intra-observer and

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inter-observer agreement in the clinical evaluations were assessed via kappa (κ)

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agreement coefficient analysis, providing an index of observed agreement against that

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which was expected by chance. The results of the κ agreement analysis were

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classified as follows: less than 0.40, poor to fair agreement; 0.40 – 0.60, moderate

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agreement; 0.60 – 0.80, substantial agreement; more than 0.80, almost perfect

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agreement [16]. Statistical analyses were conducted using SPSS (version 18.0, IBM

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Inc., Armonk, NY, USA). P-values less than 0.05 indicated a statistical significance.

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Study funding

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This study was funded by the Wenzhou Science and Technology Bureau in China

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(Y20070019).

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Results

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This study included 130 patients with a mean age of 14.98 years (standard deviation,

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2.35 years) and a male:female ratio of 38:92. Two radiologists each assessed 130

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radiographs for a total of 1040 measurements. Descriptive statistics for the C7-CSVL

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and ALAT measurements are shown in Table 1. The average of the first and second

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measurement results, by observer 1 and 2 with the same method, is calculated as the

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final mean value. In total, the mean C7-CSVL measurement was 21.49 ± 9.69 mm,

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and the mean ALAT measurement was 2.51° ± 1.09°.

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In this study, C7-CSVL was considered as a “gold standard” measurement for

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evaluating trunk imbalance. The AUC for ALAT was 0.82 (95% confidence interval

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(CI): 0.753 – 0.894, P < 0.001) for the diagnosis of trunk imbalance (Fig. 3). The

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maximum YI was 0.51 and the corresponding cut-off point was 2.59° (YI = sensitivity

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+ specificity - 1). When we defined 2.59° as the optimal cut-off value of the ALAT

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measurement，57 of 130 cases were diagnosed as trunk imbalance, 73 cases were

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trunk balance. According to the normal range 0-20 mm, 67 cases were trunk

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imbalance with C7-CSVL measurement. No statistical difference was found between

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C7-CSVL and ALAT with chi-square test for evaluating trunk imbalance (P﹥0.05).

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The intra-observer agreement values by observer 1 and 2 for the C7-CSVL

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measurement were 0.79 and 0.91, respectively. And the intra-observer agreement

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values by observer 1 and 2 for the ALAT measurement were both equal to 0.89 (Table

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2). The inter-observer agreement values for the first and second measurements with

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the C7-CSVL method were 0.78 and 0.85, respectively, and those of the ALAT

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method were 0.91 and 0.88, respectively (Table 3).

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Discussion

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Trunk balance is the manifestation of a postural strategy conditioned by anatomic and

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functional characteristics. It’s of significant importance to the patient's self-perception.

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In normal conditions, when viewed from the front, the shoulders and pelvis are

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horizontal, and the chest is centered on top of the pelvis. In patients afflicted with

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trunk imbalance, the condition contributes to altered trunk morphology, loss of

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self-confidence, depression, impaired breathing and even suicide [17, 18]. The

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purpose of treatment, including conservative treatment and surgical treatment, is to

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maximize correction, achieve stability, and restore and maintain three-dimensional

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balance [19]. A successful treatment outcome for a patient with trunk imbalance is one

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that produces a balanced trunk in the three-dimensional (coronal, sagittal and

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transverse) plane. Demaru and Yaszay [7] demonstrated that the postoperative

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decompensation rate for patients with selective thoracic fusion (STF) at a 2-year

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follow-up assessment was 31% in the group with normal trunk balance (C7-CSVL ≤ 2

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cm) and 57% in the group with trunk imbalance (C7-CSVL > 2 cm). It has also been

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reported that postoperative C7-CSVL was significantly correlated with preoperative

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C7-CSVL in scoliosis patients [20]. That is, accurately evaluating the degree of trunk

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imbalance in the coronal plane is beneficial for planning treatments and predicting

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outcomes.

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In this study, we calculated the AUC for ALAT 0.82, indicating ALAT had a good

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accuracy. Chi-square test demonstrated that no statistical difference was found

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between C7-CSVL and ALAT for evaluating trunk imbalance. However, the

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intra-observer agreement value for C7-CSVL measurement by observer 1 was

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substantial, and for ALAT measurement was perfect. It indicated that the

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intra-observer reliability of the C7-CSVL measurement was markedly less than that of

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the ALAT measurement. The intra-observer agreement of the C7-CSVL and ALAT

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measurement were both almost perfect in observer 2, indicating that both methods had

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excellent reliability by observer 2. In the inter-observer comparison, the agreement

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values for the ALAT measurement were higher than those of the C7-CSVL

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measurement in the first (0.91 > 0.78) and second (0.88 > 0.85) measurements,

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indicating that the inter-observer reliability of the ALAT was better than that of the

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C7-CSVL. This is consistent with our finding [13] that the ALAT has excellent

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intra-observer and inter-observer reliability as a method of evaluating trunk imbalance

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in the coronal plane. Therefore, we can define 2.59°as a optimal cut-off value of

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ALAT for evaluating trunk imbalance in coronal plane.

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The ALAT has several advantages in the clinic. First, precise measurement points are

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necessary for radiological measurement. The symphysis pubic is in the front of the

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body and is not influenced by intestinal contents such as gas; moreover, it can be

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clearly marked on a PACS workstation. Second, a tool for accurately measuring the

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angle of interest on a PACS workstation has been demonstrated. Finally, the

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thoracolumbar spine was the center point in full-spine standing anteroposterior

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radiography, whereas the sacrum was irregular, which made the outline of most L5

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and S1 vertebra appear indistinct and difficult to locate; however, the ALAT is not

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affected by this factor. Therefore, we suggest that the ALAT should be implemented in

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clinical settings.

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This study was aimed at analyzing the cut-off value and intra-observer and

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inter-observer agreement of the ALAT as a method for evaluating trunk imbalance in

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coronal plane. It also has some limitations. First, although the ALAT cut-off value was

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identified, larger studies are needed to validate the ALAT sufficiently. Second, this

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study only assessed adolescent patients before treatment, adults and elderly subjects

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were not studied. Therefore, future studies should extend this study to a larger subject

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pool.

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Conclusions

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We have identified the optimal cut-off value of ALAT. On the basis of the optimal

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cut-off value, the excellent agreement of ALAT has been demonstrated. Also, ALAT

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has precise measuring points and simple measuring procedures, which make it quite

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convenient assess trunk imbalance. For these reasons, ALAT should be suggested

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practice in the clinic. As the ALAT is a new method, significant further examination

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of its characteristics in people of different ages before and after treatment should be

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performed.

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References

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[1]

SRS Terminology Committee and Working Group on Spinal Classification

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Revised Glossary of Terms: by the Working Group on 3-D Classification (Chair

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Larry Lenke, MD), and the Terminology Committee, March 2000 (available at

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www.srs.org/professionals/glossary/SRS_revised_glossary_of_terms.htm#note2;

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accessed July 19, 2016).

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[2] 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):1302-1313. [3] Lenke LG, Betz RR, Harms J, et al. Adolescent idiopathic scoliosis: a new

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classification to determine exent of spinal arthrodesis. J Bone Joint Surg Am 2001;

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83-A (8): 1169-1181.

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[4] Suk SI, Lee SM, Chung ER, et al. Determination of distal fusion level with

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segmental pedicle screw fixation in single thoracic idiopathic scoliosis. Spine

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(Phila Pa 1976) 2003; 28(5):484-491.

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[6] Chen RQ, Watanabe K, Hosogane N, et al. Spinal coronal profiles and proximal

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femur bone mineral density in adolescent idiopathic scoliosis. Eur Spine J 2013;

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22(11):2433-2437.

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[7] Demura S, Yaszay B, Bastrom TP, et al. Is decompensation preoperatively a risk in Lenke 1C curves? Spine (Phila Pa 1976) 2013; 38(11):E649-655.

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[8] Li J, Hwang SW, Shi Z, et al. Analysis of radiographic parameters relevant to the

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lowest instrumented vertebrae and postoperative coronal balance in Lenke 5C

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patients. Spine (Philia Pa 1976) 2011; 36(20):1673-1678.

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[9] Sangole A, Aubin CE, Labelle H, et al. The central hip vertical axis: a reference

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21(6):1075-1081.

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[12] He JW, Yan ZH, Liu J, et al. Accuracy and repeatability of a new method for

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measuring scoliosis curvature. Spine (Phila Pa 1976) 2009; 34(9):E323–329.

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[13] Zhang RF, Liu K, Wang X, et al. Reliability of a new method for measuring

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coronal trunk imbalance, the axis-line-angle technique. Spine J 2015; 15(12):

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2459-2465.

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[14] Hong YJ, Suh SW, Modi HN et al. Centroid method: an alternative method of

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determining coronal curvature in scoliosis. A comparative study versus Cobb

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method in the degenerative spine. Spine J 2013; 13(4):421–427.

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[15] Hajian-Tilaki K. Receiver operating characteristic (ROC) curve analysis for

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[16] Hanney WJ, George SZ, Kolber MJ, et al. Inter-rater reliability of select physical

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30(5):345-352.

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[17] Trobisch PD, Samdani AF, Pahys JM, et al. Postoperative trunk shift in Lenke 1

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20(7):1137-1140.

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[18] Kotwicki T, Chowanska J, Kinel E, et al. Optimal management of idiopathic

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scoliosis in adolescence. Adolesc Health Med Ther 2013; 4:59-73. [19] Samartzis D, Leung Y, Shigematsu H, et al. Selection of fusion levels using the

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[20] Liu Z, Guo J, Zhu Z, et al. Role of the upper and lowest instrumented vertebrae in

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posterior fusion. Eur Spine J 2013; 22(11):2392-2398.

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Figure legends

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Fig. 1.

Schematic diagram of the C7-CSVL. The line (ab) parallel to the image edge

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was drawn downward from the centroid of the seventh vertebra (a) to the other end.

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The other line (cd) was drawn upward from the middle of the S1 vertebra (c) to the

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other end. The horizontal distance (e) between the two lines determined the extent of

7

trunk imbalance.

8

Fig. 2.

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C7 plumb line (ab) was drawn. The axis line (a, c) was drawn from the vertebral

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centroid of C7 (a) to the middle of the superior border of the symphysis pubis (c). The

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angle (α) at the intersection of the two lines, ab and ac, determined the extent of trunk

12

imbalance.

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Fig. 3.

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The cut-off concentration of the ALAT was 2.59° with an AUC value of 0.82.

Schematic diagram of the ALAT. Using the same radiograph as in Fig. 1, the

ROC curve analysis for the optimal cut-off point of the ALAT.

15

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Table 1. Descriptive statistics for the C7-CSVL and ALAT measurements in the

2

coronal plane (mean value and standard deviation). First

Second

measurement

measurement

(mean, SD)

(mean, SD)

1

1

Radiolog In total

ist

2

Minim

Maxim

Mean(S

um

um

D)

0.14

64.31

2

21.79 21.19 C7-CSV

21.08

21.89

(10.13 L (mm)

(9.98)

(9.73

21.49

(9.83)

(9.69)

) ) 2.52 ALAT

2.49

2.52

2.51 (1.08

(°)

(1.12)

(1.12)

2.51 0.48

(1.10)

8.93 (1.09)

) 3 4

All data were normally distributed.

5

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Table 2. Intraobserver agreement of the C7-CSVL and ALAT measurements for

2

assessing trunk imbalance in coronal plane. Methods

Kappa test Observer 1 κ-valu e

Degree of agreement

0.79

substantial

C7-CSV

3

κ-val P value ue P<

L ALAT

Observer 2

0.91 0.001*

0.89

almost perfect

P< 0.89 0.001*

Degree of agreement almost perfect almost perfect

P value P< 0.001* P< 0.001*

* P < 0.05 statistically significant.

4 5 6

Table 3. Interobserver agreement of the C7-CSVL and ALAT measurements for

7

assessing trunk imbalance in coronal plane. Methods

Kappa test First measurement κ-valu e

Degree of agreement

0.78

substantial

C7-CSV

8 9

κ-val P value ue P<

L ALAT

Second measurement

0.85 0.001*

0.91

almost perfect

P< 0.88 0.001*

Degree of agreement almost perfect almost perfect

P value P< 0.001* P< 0.001*

* P < 0.05 statistically significant.

10 11

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