Abstract

BackgroundAxial vertebral rotation (AVR) is one of the important parameters to evaluate the severity and predict the progression of scoliosis. However, the AVR measurements on radiographs may underestimate its actual value. This pilot study investigated a new three-dimensional (3D) ultrasound method to measure AVR.MethodsThree cadaveric vertebrae T7, L1, and L3 were scanned with a 3D medical ultrasound system. Nine sets of ultrasound data, the vertebral rotation from 0 to 40° with 5° increments, were recorded from each vertebra. An in-house program was developed to reconstruct and measure the 3D vertebral images. The rotation of each reconstructed vertebra was determined by the angle between the line going through the centres of either laminae (L-L) or transverse processes (TP-TP) and a reference vertical plane. Three raters measured the rotation in 3 sessions, in which they used the mouse pointer to select the L-L or TP-TP according to their knowledge of vertebral anatomy. The program detected the 3D coordinates of these points and calculated the AVR.The intra-class correlation coefficients (ICCs) were used to calculate the intra-reliability and inter-reliability. The mean absolute difference (MAD±SD) and the range of difference (RD) between the actual values and the average measurements of each rater were computed to evaluate the accuracy of methods.ResultsWhen rotation was greater than 30° for both L1 and L3, all raters found it difficult to determine one of the lamina areas due to the lack of ultrasound information in an area behind the spinous process. Therefore, the corresponding measurements were excluded. The ICC values of the intra-reliability (L-L, TP-TP) for the three raters were (0.987, 0.991), (0.989, 0.998) and (0.997, 1.000), respectively; meanwhile, the inter-reliability were 0.991 for (L-L) and 0.992 for (TP-TP). All ICC values were greater than 0.98 indicating both methods were highly reliable. The MAD±SD values (L-L, TP-TP) for the three raters were (1.5±0.3°, 1.2±0.2°), (1.6±0.3°, 1.3±0.3°), and (1.7±0.5°, 0.9±0.2°), respectively. The RD (L-L, TP-TP) were (0-4.5°, 0-3.5°), (0-5.1°, 0-4.3°), and (0-5.1°, 0-2.8°) for the three raters, respectively.ConclusionsThe (L-L) and (TP-TP) methods could be used to measure AVR reliability from the 3D ultrasound images.

Highlights

  • Axial vertebral rotation (AVR) is one of the important parameters to evaluate the severity and predict the progression of scoliosis

  • The Cobb angle and axial vertebral rotation are two major factors which can be used to measure the severity of scoliosis, estimate

  • The accuracy of the measurement method was determined based on the mean absolute difference (MAD ± SD) and the range of difference (RD) between the true values and the average measurements of each rater

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Summary

Methods

Materials and experimental setup The Ultrasonix SonixTablet (Ultrasonix Ltd., Canada), a 3D medical ultrasound system consisting of a magnetic position and orientation tracking system and a 3D Guidance device (driveBAY, Ascension Ltd., USA), was used in this study (Fig. 1). 2 shows a cadaveric vertebra attached to a protractor which is used to indicate the degree of vertebral rotation relative to the scanning wall of the container. To measure AVR, the raters used the computer mouse pointer to manually locate either the centres of laminae or the centres of transverse processes on the 3D reconstructed vertebral images according to their knowledge of vertebral anatomy. The program detected the 3D coordinates of these points and calculated the AVR based on either the centres of laminae or the centres of transverse processes. The accuracy of the measurement method was determined based on the mean absolute difference (MAD ± SD) and the range of difference (RD) between the true values and the average measurements of each rater

Results
Background
Discussion
Conclusions
Lonstein JE

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