Reliability of a new method for measuring coronal trunk imbalance, the axis-line-angle technique.
BACKGROUND
Accurate determination of the extent of trunk imbalance in the coronal plane plays a key role in an evaluation of patients with trunk imbalance, such as patients with adolescent idiopathic scoliosis. An established, widely used practice in evaluating trunk imbalance is to drop a plumb line from the C7 vertebra to a key reference axis, the central sacral vertical line (CSVL) in full-spine standing anterioposterior radiographs, and measuring the distance between them, the C7-CSVL. However, measuring the CSVL is subject to intraobserver differences, is error-prone, and is of poor reliability. Therefore, the development of a different way to measure trunk imbalance is needed.


OBJECTIVE
This study aimed to describe a new method to measure coronal trunk imbalance, the axis-line-angle technique (ALAT), which measures the angle at the intersection between the C7 plumb line and an axis line drawn from the vertebral centroid of the C7 to the middle of the superior border of the symphysis pubis, and to compare the reliability of the ALAT with that of the C7-CSVL.


METHODS
A prospective study at a university hospital was used.


METHODS
The patient sample consisted of sixty-nine consecutively enrolled men and women patients, aged 10-18 years, who had trunk imbalance defined as C7-CSVL longer than 20 mm on computed full-spine standing anterioposterior radiographs.


METHODS
Data were analyzed to determine the correlation between C7-CSVL and ALAT measurements and to determine intraobserver and interobserver reliabilities.


METHODS
Using a picture archiving and communication system, three radiologists independently evaluated trunk imbalance on the 69 computed radiographs by measuring the C7-CSVL and by measuring the angle determined by the ALAT. Data were analyzed to determine the correlations between the two measures of trunk imbalance, and to determine intraobserver and interobserver reliabilities of each of them.


RESULTS
Overall results from the measurements by the C7-CSVL and the ALAT were significantly moderately correlated. Intraobserver assessments by measuring the C7-CSVL and by doing the ALAT failed to find any significant differences between the findings from the first and second assessments by the same radiologist. Interobserver assessments significantly differed between radiologists 1 and 2 for the first assessment measuring the C7-CSVL, and between radiologists 2 and 3 for the second assessment measuring the C7-CSVL. Interobserver assessments by doing the ALAT failed to find any significant differences among the three radiologists for either of the two assessments.


CONCLUSIONS
Our results indicated that using the ALAT, which is simple and convenient, is of great value in measuring trunk imbalance. For measuring trunk imbalance, the ALAT has essential advantages compared with measuring the C7-CSVL. We encourage spine surgeons to consider using the ALAT in evaluating trunk imbalance.
Department of Radiology, The Second Affiliated Hospital of Wenzhou Medical University, 109 Xueyuanxi Rd, 325027 Wenzhou, China.
Rui-Fang
RF
Zhang
Department of Radiology, The Second Affiliated Hospital of Wenzhou Medical University, 109 Xueyuanxi Rd, 325027 Wenzhou, China.
Kun
K
Liu
Department of Radiology, The Second Affiliated Hospital of Wenzhou Medical University, 109 Xueyuanxi Rd, 325027 Wenzhou, China.
Xue
X
Wang
Department of Radiology, The Second Affiliated Hospital of Wenzhou Medical University, 109 Xueyuanxi Rd, 325027 Wenzhou, China.
Qian
Q
Liu
Department of Radiology, The Second Affiliated Hospital of Wenzhou Medical University, 109 Xueyuanxi Rd, 325027 Wenzhou, China. Electronic address: hejw505@163.com.
Jia-Wei
JW
He
Department of Spinal Surgery, The Second Affiliated Hospital of Wenzhou Medical University, 109 Xueyuanxi Rd, 325027 Wenzhou, China.
Xiang-Yang
XY
Wang
Department of Radiology, The Second Affiliated Hospital of Wenzhou Medical University, 109 Xueyuanxi Rd, 325027 Wenzhou, China. Electronic address: yanzhihanwz@163.com.
Zhi-Han
ZH
Yan
D000293:Adolescent; D000465:Algorithms; D002648:Child; D005260:Female; D006801:Humans; D008297:Male; D015588:Observer Variation; D004856:Postural Balance; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012600:Scoliosis / Q000000981:diagnostic imaging*; D060726:Torso / Q000000981:diagnostic imaging
C7–CSVL; Central sacral vertical line; Coronal trunk imbalance; Interobserver reliability; Intraobserver reliability; Radiology