Indices of torso asymmetry related to spinal deformity in scoliosis

doi:10.1016/S0268-0033(02)00099-2

Clinical Biomechanics

Volume 17, Issue 8, October 2002, Pages 559-568

https://doi.org/10.1016/S0268-0033(02)00099-2 Get rights and content

Abstract

Objective. To develop indices that quantify 360° torso surface asymmetry sufficiently well to estimate the Cobb angle of scoliotic spinal deformity within the clinically important 5–10° range.

Design. Prospective study in 48 consecutive adolescent scoliosis patients (Cobb angles 10–71°).

Background. Scoliotic surface asymmetry has been quantified on the back surface by indices such as back surface rotation (BSR) and curvature of the spinous process line and torso centroid line, though with limited success in spinal deformity estimation. Quantification of 360° torso shape may enhance surface–spine correlation and permit reduced use of harmful X-rays in scoliosis.

Methods. For each patient a 3D torso surface model was generated concurrently with postero-anterior X-rays. We computed indices describing principal axis orientation, back surface rotation, and asymmetry of the torso centroid line, left and right half-areas and the spinous process line. We calculated correlations of each index to the Cobb angle and used stepwise regression to estimate the Cobb angle.

Results. Several torso asymmetry indices correlated well to the Cobb angle (r up to 0.8). The Cobb angle was best estimated by age, rib hump and left–right variation in torso width in unbraced patients and by centroid lateral deviation in braced patients. A regression model estimated the Cobb angle from torso indices within 5° in 65% of patients and 10° in 88% (r=0.91, $standard error =6.1$ °).

Conclusion. Consideration of 360° torso surface data yielded indices that correlated well to the Cobb angle and estimated the Cobb angle within 10° in 88% of cases.
Relevance

The torso asymmetry indices developed here show a strong surface–spine relation in scoliosis, encouraging development of a model to detect scoliosis magnitude and progression from the surface shape with minimal X-ray radiation.

Introduction

With successful relation of torso surface asymmetry to scoliotic spinal deformity, scoliotic children could be monitored with fewer X-rays, reducing the attendant cancer risks [1]. While spinal curves have different locations and patterns (thoracic, thoracolumbar, lumbar) in each patient and the exact 3D spine shape would be difficult to infer from surface data alone, it is plausible that the general magnitude of spinal deformity would translate to torso asymmetry in a relatively consistent way. While clinicians have diagnosed scoliosis from visible surface asymmetry for centuries, recently surface asymmetry has been quantified using devices including the handheld “scoliometer” [2], Moire-fringe mapping [3], [4], [5], the raster-based ISIS [6], [7] and Quantec scanners [8], [9], and devices that scan 360° torso profiles [10], [11], [12], [13]. A commonly measured index of surface asymmetry is BSR [2], [14], [15], [16], [17], [18], while the palpable line of spinous processes is the most direct surface evidence of vertebral location. Correlation of indices based on these measurements to the Cobb angle (the standard radiologic measure of scoliosis) have varied by patient group and measurement method, ranging from r=0.29–0.88 for BSR [19], [20], and r=0.66–0.94 for spinous process line curvature [8], [16]. Surface deformity in scoliosis has been quantified in other ways including by asymmetry of back surface landmarks (“posterior trunk sum index”, POTSI [21]), and by the “torso Cobb angle” from the line of torso centroids, which correlated to the Cobb angle with r=0.69 [10]. No single surface-asymmetry index has been consistently well related to the Cobb angle or to other aspects of spinal deformity. We seek to estimate the magnitude of spinal deformity from a novel set of indices of 360° torso surface asymmetry, ultimately hoping to determine without use of X-rays whether spinal curvature has progressed between clinic visits. Since significant curve progression is generally defined to be an increase of 5–10° in the Cobb angle [8], [22], our goal in this study was to develop indices of torso cross-sectional asymmetry useful in estimating the Cobb angle within that range.

Section snippets

Data acquisition

Our 3D torso laser scan and X-ray system (Fig. 1) has been described previously [12]. A 360° torso surface model was generated in Matlab (The Mathworks Inc., Natick, MA, USA, v. 6.0, 2000) from data acquired by four laser topographic scanners to an accuracy of 4.2 mm [23]. The spine was reconstructed in 3D from landmarks digitized on two X-rays taken at 20° to each other while the patient remained in the same position as for the torso scan [24]. Contours were cut through the torso model at a 10

Index evaluation

Most torso asymmetry indices were best computed at levels below T7, since above this the outstretched arms confounded correlations to the Cobb angle (Table 1). Several indices predicted the Cobb angle with r≈0.75–0.8 (Table 1), including the ranges of centroid lateral deviation, principal axis rotation (“paxrotrange”) and rib hump, the left–right difference in half-centroid AP locations (“halfcenAPrange”), and the range of left–right differences in rear quarter-areas (“quarterareadiffrange”).

Technique

The four-camera scan system used here, described in detail previously [12], appeared suitable for routine clinical use. While it was somewhat more laborious to collect the entire 360° trunk surface shape than simply the back surface as most groups have done recently [8], [29], most of the indices of deformity tested here required the full torso shape for their calculation. Direct comparison of the back-surface and full-torso methods of spinal deformity estimation may become the subject of a

Conclusion

In 48 scoliosis patients, indices of torso asymmetry related to centroid lateral deviation, principal axis rotation, rib hump and differences between left and right halves of the torso correlated well with the Cobb angle (r up to 0.80), and a linear regression model using five of these indices estimated the Cobb angle within 10° in 88% of curves (r=0.91, standard error: 6.1°). This level of accuracy neared clinical usefulness in detection of a 5–10° difference in curvature and also approached

Acknowledgements

The authors thank Dr. C.-E. Aubin (Ecole Polytechnique, Montreal), Dr. N.G. Shrive (Civil Engineering, University of Calgary), Dr. C. Frank (Surgery, University of Calgary), and R. Dudley (University of Calgary) for aid in development of surface-asymmetry indices, Dr. G. Clynch (Clynch Technologies Inc., Calgary) for supporting our use of the laser scan system, N. Tardif (Ecole Polytechnique, Montreal) for evaluation of torso scanner accuracy, Dr. R. Dewar and Dr. E. Joughin (Alberta Children’s

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Our objective was to establish a corridor of normality for the external shape 3D parameters and then to assess these variables in adolescent idiopathic scoliosis (AIS).
Adolescent with mild and severe AIS were included prospectively, as well as a control group of asymptomatic subjects. A quasi‐automatic 3D reconstruction of the spine and manual 3D reconstruction of the external envelope was performed from biplanar radiography. The center of mass position, the axial intersegmental moment resulting at the apex and junctional vertebrae, and the coronal trunk balance were automatically computed. A normality corridor of asymptomatic subjects was calculated as the range [5^th-95^th percentiles] for external shape parameters at each vertebral level.
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Les études montrent que ces systèmes ont des reproductibilités de mesure tout à fait satisfaisantes tant pour les relectures d’un examen que pour la réalisation répétée d’examens [12,16,25,26]. En revanche, en raison d’un manque d’études évaluant leur capacité de dépistage des changements de l’angle de Cobb [20,24,27,28], les systèmes optiques demeurent peu utilisés [29] et de nombreuses radiographies sont effectuées pour constater une absence d’évolution. Une question se pose donc : est-il possible de réduire le nombre de radiographies dans le suivi de la scoliose idiopathique en période de croissance, en particulier chez le grand enfant et l’adolescent ?
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An increase of more than 2 degrees in any one gibbosity or in the sum of the gibbosities (in either of the two examination positions) enabled the detection of a five-degree increase in the Cobb angle with a sensitivity of 86% and a specificity of 50%.
If the present results are confirmed by other studies, analysis with back surface topography parameters may reduce the number of X-ray examinations required to detect increases in the Cobb angle.
L’évolution de la scoliose idiopathique de l’adolescent est classiquement contrôlée par un suivi radiographique régulier. L’angle de Cobb, mesuré sur des radiographies de rachis entier, est considéré comme le gold standard de ce suivi.
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Cent patients âgés de 13,3 ans en moyenne et présentant des angles de Cobb de plus de 10 degrés ont été inclus. Les mesures des paramètres topographiques étaient réalisées dans une position standard et dans une position permettant de dégager les omoplates. Les paramètres topographiques testés étaient les gibbosités et les courbures rachidiennes.
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These systems have been built highly parameterized for a specific type of analysis. Most of these systems only treat specific areas of the body, primarily the spinal deformities [23,24,32,30,31]. The solution more frequently applied to measure body posture consists of the installation and alignment of multiple cameras, applying stereo vision methodologies [3,4].
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Anthropometric tables are not applicable to calculate the scoliotic trunk mass and center of mass (COM). The purposes of this study were: (1) to estimate the head and trunk mass and COM in able-bodied and scoliotic girls using a force plate method, (2) to estimate head and trunk COM offset compared to those of the body, and (3) the use of mean ratios to estimate the head and trunk COM calculated in this study and that calculated according to a conventional three-dimensional (3D) method compared to the measured values. Twenty-one scoliotic and twenty able-bodied girls participated. The subjects stood upright with arms beside the trunk on a force plate that collected data at 60 Hz for a period of 5 s. The anteroposterior and mediolateral positions of the body COM were obtained from the mean center of pressure values. The height of the body COM was estimated by the reaction board method. Afterwards a body segment was displaced and changes in force plate readings were recorded and applied to estimate the head and trunk mass and COM. Trunk offset was defined as the difference between the COM of the body and head and trunk. The measured head and trunk COM was compared to values obtained by the mean ratios calculated from this study and given by the conventional 3D method. The relative head and trunk mass and the anteroposterior trunk offset were larger in scoliotic girls. The force plate method gave similar results to measured COM values for both groups underlying its capability to provide a more accurate estimation of COM related values. Thus, the use of mean ratios of 0.5538 and 0.6438 obtained in this study to estimate the head and trunk mass and COM position in scoliotic girls can overcome the main drawbacks of current anthropometric methods, if direct measurements cannot be taken.
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Scoliosis is characterized by a lateral curvature of spine in the coronal plane of at least 10°, showing three-dimensional deformities of the torso. Recently, a 3D body scanner was proposed as an ionizing radiation-free method, supplementary to clinical examinations and X-rays, for assessing scoliosis and its progression. Here we present an automatic method of analysis of the 3D images of the body torso delivered by the scanner, with the objective of capturing and characterizing deformities in the torso due to scoliosis. The method quantifies asymmetries in each of the torso contours, extracted from 2D cross sections of the 3D torso images, transverse to the vertical axis of the body. Three parameters were calculated: (1) circularity, (2) difference between the areas to left and right of the spinous process (LRAsm), and (3) difference between the ratios width/depth to the left and right of the centroid of the contour (ASR). The method was verified by analyzing twenty-six computed tomography images of patients with different types of scoliosis. In patients with thoracic scoliosis both LRAsm and ASR were larger, that is the asymmetry was stronger, in the thoracic than in the lumbar region, whilst in patients with lumbar scoliosis the inverse was obtained. Furthermore, larger values of LRAsm coincided with the apex position of scoliosis. The circularity factor did not capture scoliosis-related asymmetries. It may, however, be useful in localizing the vertebral level during analysis of 3D scanner data. The method can have the potential to use it for follow-up examinations of scoliosis, in addition to clinical examinations. Further validation of the method requires its application to 3D body scanner data, particularly for more cases of severe scoliosis, which have more irregular transverse contours and thus potential for improvement.

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Indices of torso asymmetry related to spinal deformity in scoliosis

Abstract

Introduction

Section snippets

Data acquisition

Index evaluation

Technique

Conclusion

Acknowledgements

J. Biomech.

Clin. Biomech.

Reducing the lifetime risk of cancer from spinal radiographs among people with adolescent idiopathic scoliosis

Spine

An objective criterion for scoliosis screening

J. Bone Joint Surg. [Am]

Moire fringe topography of the human body

Med. Instrum.

The role of Moire photography in evaluating minor scoliotic curves

Int. Orthop.

Ten-year follow-up evaluation of a school screening program for scoliosis. Is the forward-bending test an accurate diagnostic criterion for the screening of scoliosis?

Spine

ISIS scanning: a useful assessment technique in the management of scoliosis

Spine

Early detection of progression in adolescent idiopathic scoliosis by measurement of changes in back shape with the integrated shape imaging system scanner

Spine

Surface topography, Cobb angles and cosmetic change in scoliosis

Spine

Relationship between Quantec measurement and Cobb angle in patients with idiopathic scoliosis

J. Pediatr. Orthop.

Optoelectronic evaluation of trunk deformity in scoliosis

Spine

Automated 360° profilometry of human trunk for spinal deformity analysis

Reconstruction of laser-scanned 3D torso topography and stereo-radiographical spine and rib-cage geometry in scoliosis

Comp. Meth. Biomech. Biomed. Eng.

Accurate and fast non-contact 3D acquisition of the whole trunk

Prediction of scoliotic cobb angle with the use of the scoliometer

Spine