Spine Deformity 2 (2014) 81e88www.spine-deformity.org

Basic Science

Computer-Generated, Three-Dimensional Spine Model From BiplanarRadiographs: A Validity Study in Idiopathic Scoliosis Curves Greater

Than 50 DegreesJoseph H. Carreau, MDa, Tracey Bastrom, MAb, Maty Petcharaporn, BSb, Caitlin Schulte, BSb,

Michelle Marks, PT, MAb, Tam�as Ill�es, MD, DScc, Szabolcs Somoske€oy, MDd,Peter O. Newton, MDb,*

aDepartment of Orthopaedics, University of California, San Diego, 9500 Gilman Drive, San Diego, CA 92093, USAbRady Children’s Hospital and Health Center, San Diego, 3020 Children’s Way, San Diego, CA 92123, USAcOrthopedic and Trauma department in CHU - Brugmann, Universit�e Libre de Bruxelles, Brussels, Belgium

dDepartment of Orthopedic Surgery Institute of Musculoskeletal Surgery, University of P�ecs, 1 Ak�ac utca, P�ecs H-7632, Hungary

Received 2 October 2012; revised 30 September 2013; accepted 8 October 2013

Abstract

Study Design: Reproducibility study of SterEOS 3-dimensional (3D) software in large, idiopathic scoliosis (IS) spinal curves.Objective: To determine the accuracy and reproducibility of various 3D, software-generated radiographic measurements acquired from a2-dimensional (2D) imaging system.Summary of Background Data: SterEOS software allows a user to reconstruct a 3D spinal model from an upright, biplanar, low-dose,X-ray system. The validity and internal consistency of this system have not been tested in large IS curves.Methods: EOS images from 30 IS patients with curves greater than 50� were collected for analysis. Three observers blinded to the studyprotocol conducted repeated, randomized, manual 2D measurements, and 3D software generated measurements from biplanar imagesacquired from an EOS Imaging system. Three-dimensional measurements were repeated using both the Full 3D and Fast 3D guidedprocesses. A total of 180 (120 3D and 60 2D) sets of measurements were obtained of coronal (Cobb angle) and sagittal (T1eT12 andT4eT12 kyphosis; L1eS1 and L1eL5; and pelvic tilt, pelvic incidence, and sacral slope) parameters. Intra-class correlation coefficientswere compared, as were the calculated differences in values generated by SterEOS 3D software and manual 2D measurements. The 95%confidence intervals of the mean differences in measures were calculated as an estimate of reproducibility.Results: Average intra-class correlation coefficients were excellent: 0.97, 0.97, and 0.93 for Full 3D, Fast 3D, and 2D measures,respectively (p 5 .11). Measurement errors for some sagittal measures were significantly lower with the 3D techniques. Both the Full 3Dand Fast 3D techniques provided consistent measurements of axial plane vertebral rotation.Conclusions: SterEOS 3D reconstruction spine software creates reproducible measurements in all 3 planes of deformity in curves greaterthan 50�. Advancements in 3D scoliosis imaging are expected to improve our understanding and treatment of idiopathic scoliosis.� 2014 Scoliosis Research Society.

Keywords: Scoliosis; Idiopathic scoliosis; SterEOS 3D Spine Software; Upright biplanar scanning X-ray; EOS

Author disclosures: JHC (grant from EOS Imaging); TB (grant from EOS Imaging); MP (grant from EOS Imaging); CS (grant from EOS Imaging);MM (grant

fromEOS Imaging; boardmembershipwith Setting Scoliosis Straight Foundation; consultancy for DePuy Synthes Spine); TI (none); SS (none); PON (boardmem-

bership with POSNA, Harms Study Group Foundation, Scoliosis Research Society, Children’s Specialist Foundation; consultancy for DePuy Spine, Stanford Uni-

versity; employment with Children’s Specialists of San Diego; expert testimony for NorCal, law firm Carroll, Kelly, Trotter, Franzen, &McKenna, law firm Smith,

Haughey, Rice & Roegge; grants from NIH, OREF, POSNA, SRS, Harms Study Group Foundation, DePuy Synthes Spine, Axial Biotech, Biospace/Med/EOS

Imaging; payment for lectures including service on speakers bureaus from DePuy Spine; patents from DePuy Synthes Spine; royalties from DePuy Synthes Spine,

Thieme Publishing; payment for development of educational presentations from DePuy Synthes Spine; stock/stock options from Nuvasive).

This work was supported by a grant from EOS Imaging to the Setting Scoliosis Straight Foundation (FKA Harms Study Group Foundation) and by the

Rady Children’s Hospital Orthopedic Research and Education Fund. No direct financial benefits were received in support of this work.

*Corresponding author. Rady Children’s Hospital, 3020 Children’s Way, San Diego, CA 92123, USA. Tel.: (858) 966-6789; fax: (858) 966-8519.

E-mail address: pnewton@rchsd.org (P.O. Newton).

2212-134X/$ - see front matter � 2014 Scoliosis Research Society.

http://dx.doi.org/10.1016/j.jspd.2013.10.003

82 J.H. Carreau et al. / Spine Deformity 2 (2014) 81e88

Introduction Materials and Methods

Advancements in imaging technology have improvedthe understanding and treatment algorithm of many pedi-atric orthopedic conditions. Specifically, improvements in3-dimensional (3D) imaging technology, such as 3Dcomputed tomography (CT), have the potential to improvethe methods with which patients with scoliosis are analyzedand treated [1]. Unfortunately, the benefits of CT imagingcome with risks because radiation exposure may be asso-ciated with increased lifetime cancer risk in the pediatricpopulation [2,3]. This concern has led to the interest in anddevelopment of advanced imaging techniques with reducedradiation load to the patient.

The EOS System (EOS Imaging, Paris, France) is aUnited States Food and Drug Administrationecleared,upright, biplanar scanning imaging system that acquiresboth posterior-anterior (PA) and a lateral (Lat) imagessimultaneously. This system is equipped with a slot-scanner and novel X-ray particle detector that use only10% of the radiation that conventional radiographs use [3].Recently, a patented software system was released, Ste-rEOS (EOS Imaging), which allows the user to reconstructa 3D model of a spine from the PA and Lat images ac-quired from the EOS Imaging System (Fig. 1). The aim ofthis study was to test the reliability of this spinal softwarein surgical range idiopathic scoliosis (IS) curves. There-fore, curves greater than 50� were selected for study.Furthermore, an expedited and simplified Fast 3D tech-nique has become available, but the reliability has yet to bescrutinized. If the software produces valid and reproducible3D information about a spinal curve, it may be a valuableclinical tool for evaluation of and surgical planning forpatients with IS.

Fig. 1. Example of a typical 3-dimensional, T1eL5 spine model

After institutional review board approval was obtained,30 IS patients were retrospectively enrolled from 2 sites(P�ecs, Hungary, and San Diego, CA). With b 5 0.1 anda 5 0.05, a power analysis was conducted; N 5 30 wasjustified as the number needed to find clinically significantdifferences between 2-dimensional (2D) and 3D tech-niques. Patients were included in the study if they had adiagnosis of IS and a major thoracic curve greater than 50�,if they were of age 7e16 years, and if they had acquired PAand Lat EOS images as part of their clinical care. Patientswere then subdivided into 3 groups based on curve size(50� to 59�, 60� to 69�, and 70� or more), with 10 patientsin each group.

One orthopedic research resident in training, who wasspending a year dedicated to scoliosis research, and 2research specialists with experience in 2D spine measure-ments for data collection conducted repeated, randomized,2D manual measurements and 3D reconstructions on eachset of films. After uploading a patient’s PA and Lat EOSimages into the 2D SterEOS workstation, coronal (Cobbangle) and sagittal (T1e12 kyphosis, T4e12 kyphosis,L1eS1 lordosis, L1eL5 lordosis, pelvic tilt, pelvic inci-dence, and sacral slope) measurements were conductedmanually in 2D. These measurements were conducteddigitally in the 2D mode of the SterEOS software work-station and were repeated at separate intervals to assessreproducibility. The measurements were repeated at 2separate intervals to lessen the likelihood that recall wouldinfluence the measurements performed. With some vari-ability, the second interval was performed on average 5e7days later. The methods by which these measurements wereconducted were as they would be in clinical practice.

(right) generated from biplanar, 2-dimensional images (left).

Fig. 2. The sacral slope is defined in the sagittal plane (line), and the cen-

ter of the right and left femoral heads (circles) in both frontal and sagittal

planes.

83J.H. Carreau et al. / Spine Deformity 2 (2014) 81e88

Three-dimensional reconstructions were performed andrepeated in both the traditional, Full 3D method and the new,Fast 3D method. In both techniques, this was performed byfirst defining the pelvic parameters. As guided by the soft-ware, the sacral slope was defined sagittally, and thereafterthe circumferences of the acetabulae were traced in both 2Dimages (Fig. 2). Next, a digital spline was drawn down thecenter of the patient’s spine in both the PA and Lat 2D imagesfrom the superior end plate of T1 to the inferior end plate ofL5. The computerized contour was manually adjusted to bestfit the native spinal curve. A computer-estimated width of thevertebral bodies was also generated andmanually adjusted tobest approximate the native spine dimensions (Fig. 3). After aclose estimation of spinal contour, height, and width wasachieved, a computer-generated best-fit template of a spinewas created to overlap the patient’s native spinal image inboth planes. From this template, the curves could be auto-matically or manually selected and end plates and apicalvertebrae defined (Fig. 4). From here, stepwise coarse andfine adjustments of the overlapped digital vertebral bonyanatomy were performed to match the native spine anatomy.This was first done by adjusting the size and orientation (tiltand rotation) of every vertebral bodymodel to obtain the best

Fig. 3. The upper and lower end plates of the spine are defined (horizontal lines

line). A manual adjustment of vertebral column width (dashed vertical lines) is p

digital template to the contour and size of the patient’s anatomy.

match to the native image anatomy. Then, a fine adjustmentof the shape of the vertebrae was performed by adjusting themodel until its contours perfectly overlap the vertebral

) and the center of the spine column is drawn with a spline (solid vertical

erformed in the postero-anterior and lateral planes to best approximate the

Fig. 4. After defining column dimensions, a computer-generated model of the patient’s spine is generated. The end and apical vertebra(e) of the major spinal

curve(s) can be selected (green).

Fig. 5. Manual adjustments of various landmarks are performed to match the size, shape, slope, and rotation of the digital template to the radiographic bony

anatomy. Images before (top) and after (bottom) fine adjustments were performed in the postero-anterior and lateral planes (left and right, respectively).

84 J.H. Carreau et al. / Spine Deformity 2 (2014) 81e88

Fig. 6. Three-dimensional model generated after reconstruction, with end

vertebra (blue) and apices (yellow) highlighted in the spinal curves.

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radiographic contours. In the Full 3D technique, this fineshape adjustmentwas done in a stepwise fashion beginning atL5 and working proximally to end at T1 (Fig. 5). In theFast3D technique, this detailed shape adjustment was doneonly at the end and apical vertebrae of defined curves, whichexpedited the reconstruction process. When the user wassatisfied with the adjustments made, the 3D model recon-struction was considered complete (Fig. 6). The softwaregenerated the 8 2D coronal and sagittal measurements

Fig. 7. Schematic of the machine (left) and patient (right)

mentioned earlier. In addition, 3D data of axial rotation (indegrees) about the apex of the selected curves were gener-ated. In the Full 3D reconstruction process, the axial rotationof all other vertebrae was also calculated, as every vertebralmodel was accurately adjusted.

Because the 3D radiographic data were softwaregenerated, the procedure was done according to a plane ofreference. The reference was defined by the axis of thepatient’s acetabulae as they relate to the parallel axis of themachine (Fig. 7). Because EOS image acquisition is con-ducted with the patient upright, the radiographic parametersmay vary slightly; therefore, measurements may be gener-ated according to the ‘‘patient’’ or ‘‘machine’’ frame ofreference. If the patient is standing in plane with the ma-chine, both machine and patient reference values will be thesame. Clinical parameters calculated in the patient frameare thus not affected by patient position during acquisition,unlike clinical parameters calculated in the machine frame,which may be more comparable to conventional, 2D mea-surements in which adjustments for slight patient rotationare not possible. Measurements in both of these planes werecollected for comparison.

Statistical analysis

The 2D manual measurements were compared with theSterEOS Full 3D reconstruction measures using repeated-measures analysis of variance (RMANOVA) in themachine reference plane. Similarly, the SterEOS 3D mea-surements calculated in the patient reference frame afterFull 3D reconstruction were compared with the SterEOSmeasurements calculated in the patient frame after Fast 3Dreconstruction using RMANOVA.

Reproducibility of the measures was assessed bycalculating the mean difference for each patient, and theoverall mean difference for all the patients. Using standarderror of the mean difference � 1.96, ranges for calculatingthe 95% confidence intervals were obtained. The upper

planes of reference as related to the imaging system.

Table 1

Repeated-measures analysis of variance comparing 2-dimensional and

3-dimensional radiographic measurements.

Radiographic parameter ( �) Mean Standard

deviation

N p value

3D Cobb angle 67.1 12.8 90 .874

2D Cobb angle 67.2 12.5 90

3D kyphosis T1eT12 28.9 19.7 90 !.001

2D kyphosis T1eT12 33.9 17.5 90

3D kyphosis T4eT12 21.0 19.4 90 !.001

2D kyphosis T4eT12 26.5 16.8 90

3D lordosis L1eL5 45.5 12.2 90 .075

2D lordosis L1eL5 43.9 13.8 90

3D lordosis L1eS1 54.3 15.7 90 .546

2D lordosis L1eS1 53.8 14.8 90

3D pelvic incidence 48.7 13.9 90 .497

2D pelvic incidence 48.3 13.7 90

3D sagittal pelvic tilt 6.9 7.6 90 .630

2D sagittal pelvic tilt 6.7 7.4 90

3D sacral slope 41.8 10.1 90 .785

2D sacral slope 41.7 10.2 90

2D, 2-dimensional; 3D, 3-dimensional.

Manual 2D versus Full 3D reconstruction values in machine frame of

reference. Two-dimensional measurements of thoracic kyphosis were

larger on average, and were statistically significant from 3D-generated

values.

86 J.H. Carreau et al. / Spine Deformity 2 (2014) 81e88

bound of the 95% confidence interval was identified as themaximum standard error of measurement.

The average difference in inter-rater measurement (mea-surement error) for the 2D manual measurements versus themachine frame Full 3D SterEOS 3D reconstruction wascompared with RMANOVA. Similarly, the average differ-ence in measurements for SterEOSmeasurements calculatedin patient frame after Full 3D reconstruction were comparedwith the SterEOS measurements calculated in patient frameafter Fast 3D reconstruction using RMANOVA. In addition,the patient and machine frame of reference values werecompared using RMANOVA.

Intra-rater and Inter-rater reliability of the 2D radio-graphic measures, SterEOS measurements calculated afterFull 3D reconstruction, and SterEOS measurementscalculated after Fast 3D reconstruction were assessed usingthe intra-class correlation coefficient (ICC). For the Ste-rEOS measurements, these were calculated for both thepatient and machine frame values. To assess overall reli-ability, the average ICCs were compared between 2D, Full3D, and Fast 3D measures using analysis of variance.

All analysis of varianceedependent variables werechecked for normality and homogeneity of variances.Alpha was set at p ! .05 to declare significance.

Table 2

Repeated-measures analysis of variance comparing measurement error of

2-dimensional and 3-dimensional techniques.

Radiographic parameter ( �) Mean Standard

deviation

N p Value

3D Cobb angle 2.64 2.66 90 .975

2D Cobb angle 2.63 2.86 90

Results

Three observers conducted a total of 540 sets of mea-surements (60 2D, 60 Full 3D, and 60 Fast 3D reconstructionseach). Overall, the average time spent performing a Full 3Dreconstruction was 21 � 10 minutes, compared with 12 � 2minutes for Fast 3D reconstruction. The time spent per-forming a 3D reconstruction decreased with increasingexperience; thus, by study completion, time spent recon-structing decreased to 13� 3 and 11� 2 minutes in the Full3D and Fast 3D methods, respectively (Fig. 8).

When comparing 2D manual measurements with Full 3Dreconstruction measurements in the machine frame ofreference, statistically significant differences (p ! .001) in

Fig. 8. Average time (in minutes) spent performing a 3-dimensional (3D)

reconstruction between observers over time. Each set of reconstructions

(1e6) includes 10 reconstructions. The time spent reconstructing each

spine decreased significantly as experience increased.

the mean of sagittal measurements of thoracic kyphosis werenoted. Interestingly, all average 2D values of kyphosis werelarger than 3D-generated values (Table 1). Furthermore,when averaging the difference in repeated measurementswithin observers, measurement error in 2D was significantlyhigher (p ! .001) than 3D in all measures of kyphosis andlordosis (Table 2). To compare the two 3D reconstruction

3D kyphosis T1eT12 4.44 3.11 90 !.001

2D kyphosis T1eT12 10.40 8.61 90

3D kyphosis T4eT12 4.26 4.12 90 !.001

2D kyphosis T4eT12 7.06 6.55 90

3D lordosis L1eL5 3.82 2.62 90 !.001

2D lordosis L1eL5 6.33 5.32 90

3D lordosis L1eS1 3.28 2.49 90 !.001

2D lordosis L1eS1 5.98 6.28 90

3D pelvic incidence 3.22 3.05 90 .2

2D pelvic incidence 2.78 2.72 90

3D sagittal pelvic tilt 1.12 1.10 90 .355

2D sagittal pelvic tilt 0.99 0.95 90

3D sacral slope 2.84 2.85 90 .483

2D sacral slope 2.60 2.43 90

2D, 2-dimensional; 3D, 3-dimensional.

Average measurement error of repeated 2D measurements compared

with 3D reconstructions in machine frame of reference. Overall, mea-

surement error was higher in manual 2D sagittal measurements of kyphosis

and lordosis.

Table 3

Repeated-measures analysis of variance comparing Full and Fast methods

of 3-dimensional reconstruction.

Radiographic parameter ( �) Mean Standard

deviation

N p value

Full Cobb angle 66.2 12.4 90 .553

Fast Cobb angle 66.0 12.1 90

Full rotation 22.2 11.2 90 .784

Fast rotation 22.3 10.9 90

Full kyphosis T1eT12 27.6 20.1 90 .788

Fast kyphosis T1eT12 27.8 20.4 90

Full kyphosis T4eT12 19.4 20.3 90 .179

Fast kyphosis T4eT12 19.9 20.6 90

Full lordosis L1eL5 44.7 12.6 90 .397

Fast lordosis L1eL5 45.0 13.0 90

Full lordosis L1eS1 53.4 16.3 90 .620

Fast lordosis L1eS1 53.2 16.5 90

Full pelvic incidence 48.6 13.8 90 .752

Fast pelvic incidence 48.7 14.1 90

Full sagittal pelvic tilt 6.9 7.6 90 .340

Fast sagittal pelvic tilt 7.0 7.7 90

Full sacral slope 41.7 10.0 90 .935

Fast sacral slope 41.7 10.2 90

Comparison of the traditional Full versus the new Fast methods of

3-dimensional reconstruction. There were no significant differences be-

tween the 2 techniques.

87J.H. Carreau et al. / Spine Deformity 2 (2014) 81e88

methods, measurements were averaged in the patient refer-ence frame after Full 3D and Fast 3D reconstructions. Nosignificant differences in mean measurement were revealedbetween the 2 methods (Table 3). A comparison of machineversus patient plane of reference was also conducted withRMANOVA for each radiographic parameter. Small but

Table 4

Repeated-measures analysis of variance of machine versus patient plane of

reference.

Radiographic parameter ( �) Mean Standard

deviation

N p value

Machine Cobb angle 67.1 12.8 90 !.001

Patient Cobb angle 66.2 12.4 90

Machine rotation 22.6 10.9 90 .309

Patient rotation 22.2 11.2 90

Machine kyphosis T1eT12 28.9 19.7 90 !.001

Patient kyphosis T1eT12 27.6 20.1 90

Machine kyphosis T4eT12 21.0 19.4 90 !.001

Patient kyphosis T4eT12 19.4 20.3 90

Machine lordosis L1eL5 45.5 12.2 90 .01

Patient lordosis L1eL5 44.7 12.6 90

Machine lordosis L1eS1 54.3 15.7 90 !.001

Patient lordosis L1eS1 53.4 16.3 90

Machine pelvic incidence 48.7 13.9 90 .198

Patient pelvic incidence 48.6 13.8 90

Machine pelvic tilt 6.9 7.6 90 .832

Patient pelvic tilt 6.9 7.6 90

Machine sacral slope 41.8 10.1 90 .297

Patient sacral slope 41.7 10.0 90

Comparison of radiographic values generated in the patient versus the

machine plane of reference. Overall, patient frame of reference values

tended to be smaller, and were statistically significant in several measures

(bold). However, the differences were small and likely of little clinical

significance.

statistically significant differences were noted in severalvalues (Table 4). As an assessment of reproducibility, ICCswere calculated to measure consistency within and betweenobservers. For reference, as an ICC value approaches 1.0, itdemonstrates less variability, and thus better consistency.The intra-rater ranges of ICCs in 2D measures and 3D Full3D and Fast 3D reconstructions were all above 0.95. Theinter-rater ICCswere also in similar ranges in 2D and both 3Dmethods (Table 5). Overall, the ICC data suggested excellentmeasurement consistency with 2D and both 3D techniques.

Discussion

Understanding scoliosis as a 3D deformity is of greatimportance, and using 3D data via CT in corrective surgeryhas been suggested to improve clinical outcomes [4].Although the perception of the progressive deformity islargely 3D, the evaluation and classification is based on 2Dradiographic assessments [5]. The Scoliosis Research Soci-ety established a committee to propose a new 3D classifica-tion for scoliosis. After reviewing data from 409 3D spines, atop-down or da Vinci view of end-apex-end planes of cur-vature was found to be both valid and clinically useful [1].Various methods to characterize the spine in 3D have beenproposed, and thus imply a cumulative interest in redefiningspinal deformity in 3D [6]. However, for this to be donesuccessfully, the acquisition of 3Ddatamust be both practicaland without significant radiation exposure to the patient.

The EOS Imaging system is a biplanar, upright scanningimaging modality that is equipped with a slotted scannerand a novel, Nobel prizeewinning, multiwire, proportionalX-ray detection chamber. These combined attributes reduceX-ray particle scatter, improve image quality, and signifi-cantly reduce the radiation load to the patient [3].Furthermore, using SterEOS 3D software, a 3D spinemodel can be acquired from biplanar radiographs, andstandard radiographic data can be generated. The methodby which the computer software generates a 3D model wasinitially tested against 3D CT and was found to be bothprecise and accurate [7]. This study tested the validity ofthe software to produce reliable 3D measurements in curvesgreater than 50�, and demonstrated reproducible results.However, assessing the software’s accuracy is lessstraightforward. To do so, the authors compared manual 2Dmeasurements with 3D-generated measurements and foundstatistically significant differences in lateral measurementsof kyphosis. The data also revealed significantly highermeasurement error within these same regions in the manual2D measurements. High 2D sagittal measurement error asseen in the thoracic spine is not a novel finding and isconsistent with prior published data [8]. The higher 2Dmeasurement error noted is likely an effect of shadowing ofnative anatomy by ribs, lung fields, and the chest wall,which can make bony anatomy such as end plates difficultto define and integrate into a measurement. The ability ofSterEOS to track the spinal contour in these regions may

Table 5

Reproducibility of each radiographic parameter.

Radiographic parameter ( �) Intra-rater reliability Inter-rater reliability

Full 3D range Fast 3D range 2D range Full 3D Fast 3D 2D

Minimum Maximum Minimum Maximum Minimum Maximum

Cobb angle 0.983 0.989 0.982 0.991 0.991 0.996 0.975 0.975 0.984

Rotation 0.978 0.994 0.974 0.989 n/a n/a 0.986 0.985 n/a

Kyphosis T1eT12 0.973 0.991 0.980 0.988 0.974 0.993 0.987 0.967 0.962

Kyphosis T4eT12 0.982 0.994 0.973 0.986 0.982 0.994 0.982 0.979 0.959

Lordosis L1eL5 0.955 0.969 0.972 0.988 0.970 0.994 0.966 0.944 0.95

Lordosis L1eS1 0.976 0.985 0.969 0.991 0.953 0.993 0.906 0.941 0.953

Pelvic incidence 0.980 0.991 0.979 0.991 0.992 0.995 0.984 0.991 0.841

Sagittal pelvic tilt 0.994 0.997 0.994 0.999 0.997 0.998 0.993 0.997 0.945

Sacral slope 0.957 0.989 0.966 0.985 0.983 0.993 0.976 0.972 0.862

2D, 2-dimensional; 3D, 3-dimensional; n/a, not available.

Range of intra-class and inter-class correlation coefficients for repeated measurements within and between observers, respectively. Overall, the intra-class

correlations were within an excellent range in 2D and each 3D technique, suggesting excellent reproducibility and internal consistency.

88 J.H. Carreau et al. / Spine Deformity 2 (2014) 81e88

provide it with an advantage over 2D manual measure-ments, and thus produce more consistent data. It isimportant to recognize, though, that a lower measurementerror found in the 3D techniques in sagittal measurementsdoes not necessarily equate to improved accuracy. Thisstudy evaluated the ability of a 3D spine model to generatevarious clinical measurements that may not in fact bestcharacterize a 3D deformity. In 2009, a study compared 2vertebral levels above and below the thoracic apex (5vertebrae) in both 2D and 3D in 66 patients [9]. The 3Dreconstructions were then rotated to achieve a true lateralview of the apical thoracic vertebra, and the sagittal apicalcurvature was re-measured. The true apical sagittal profilewas found to be overestimated by an average of 10�

compared with the perceived alignment from standardlateral radiographs. These findings suggest a limitation inthe accuracy of 2D measurements as a means to charac-terize a 3D deformity. The results of the current data par-allel this and emphasize the importance of improving theway surgeons define a 3D deformity such as scoliosis.

This study showed that SterEOS provides reproduciblemeasurements of Cobb angle, T1eT12 kyphosis, T4eT12kyphosis, L1eS1 lordosis, L1eL5 lordosis, pelvic tilt,pelvic incidence, sacral slope, and apical vertebral rotation.The software also generated sagittal measurements ofkyphosis and lordosis with less measurement error than themanual, 2D technique. Furthermore, there were no signif-icant differences in the new, Fast 3D method of 3Dreconstruction compared with the Full 3D method in any2D measurements or 3D axial rotation. The time spentperforming a 3D reconstruction decreased significantlywith experience, and may be an efficient system for clin-ical practice.

These findings suggest that SterEOS 3D software mayprovide the spinal deformity surgeon with a useful adjunctwhen characterizing and planning the surgical treatmentof patients with adolescent idiopathic scoliosis. Furtherstudy into characterizing 3D spinal deformity is essentialfor improving the understanding of scoliosis and opti-mizing treatment.

References

[1] Labelle H, Aubin CE, Jackson R, et al. Seeing the spine in 3D: how

will it change what we do? J Pediatr Orthop 2011;31(1 Suppl):

S37e45.[2] Brenner DJ. Should we be concerned about the rapid increase in CT

usage? Rev Environ Health 2010;25:63e8.

[3] Deschenes S, Charron G, Beaudoin G, et al. Diagnostic imaging

of spinal deformities: reducing patients radiation dose with a new

slot-scanning X-ray imager. Spine (Phila Pa 1976) 2010;35:989e94.

[4] Hong JY, Suh SW, Easwar TR, et al. Evaluation of the three dimen-

sional deformities in scoliosis surgery with computed tomography:

efficacy and relationship with clinical cutcomes. Spine (Phila Pa

1976) 2011;36:E1259e65.

[5] Negrini S, Negrini A, Atanasio S, Santambrogio GC. Three-dimen-

sional easy morphological (3-DEMO) classification of scoliosis,

part I. Scoliosis 2006;1:20.

[6] Illes T, Tunyogi-Csapo M, Somoske€oy S. Breakthrough in three-

dimensional scoliosis diagnosis: significance of horizontal plane view

and vertebra vectors. Eur Spine J 2011;20:135e43.[7] Humbert L, de Guise JA, Aubert B, et al. 3D reconstruction of the

spine from biplanar X-rays using parametric models based on trans-

verse and longitudinal inferences. Med Eng Physics 2009;31:

681e7.

[8] Kuklo TR, Potter BK, O’Brien MF, et al. Reliability analysis for dig-

ital adolescent idiopathic scoliosis measurements. J Spinal Disord

Tech 2005;18:152e9.

[9] Hayashi K, Upasani VV, Pawelek JB, et al. Three-dimensional anal-

ysis of thoracic apical sagittal alignment in adolescent idiopathic

scoliosis. Spine (Phila Pa 1976) 2009;34:792e7.