Idiopathic scoliosis in children and adolescents: assessment with a biplanar X-ray device
Insights into Imaging volume 5, pages 571–583 (2014)
Idiopathic scoliosis is one of the most common conditions encountered in paediatric practice. It is a three-dimensional (3D) spinal deformity. Conventional radiography is still the modality of choice for evaluation of children and adolescents with idiopathic scoliosis, but it requires repeat radiographs until skeletal maturity is reached and does not provide information about spinal deformity in all three planes. A biplanar X-ray device is a new technique that enables standing frontal and lateral radiographs of the spine to be obtained at lowered radiation doses. With its specific software, this novel vertical biplanar X-ray unit provides 3D images of the spine and offers the opportunity of visualising the spinal deformity in all three planes. This pictorial review presents our experience with this new imaging system in children and adolescents with idiopathic scoliosis.
• The biplanar X-ray device produces two orthogonal spine X-ray images in a standing position.
• The biplanar X-ray device can assess idiopathic scoliosis with a lower radiation dose.
• The biplanar X-ray device provides 3D images of the spine.
Scoliosis is defined on radiographs by the presence of one or more lateral curvatures of the spine in the coronal plane, greater than 10° as measured by the Cobb method . There are no identifiable causes for this condition in about 80 % of cases and, in particular, no evidence of congenital, developmental or neuromuscular abnormalities . On the basis of patient’s age and clinical features, idiopathic scoliosis is categorised as infantile (0–3 years) scoliosis (male predominance, levoscoliosis more frequent), juvenile (4–10 years) scoliosis (female predominance, dextroscoliosis more frequent) and adolescent (11–18 years) scoliosis (female predominance, dextroscoliosis more frequent) .
Radiography is the mainstay to confirm the diagnosis of idiopathic scoliosis in excluding underlying causes (e.g. segmentation abnormalities), to characterise the type of spinal curvature(s), determine the flexibility of the curvature(s), follow disease progression and monitor treatment. Standard evaluation consists of standing frontal radiographs of the entire spine (either anteroposterior [AP] views in males or posteroanterior [PA] views in females in order to reduce the radiation dose to the breasts), sometimes completed by lateral radiographs. However, radiography has two main disadvantages. Firstly, repeated examinations (it is estimated that a typical scoliosis patient will have approximately 22 radiological examinations over a 3-year treatment period ) are responsible for an increased amount of radiation exposure and, particularly in young females, an increased risk of breast cancer or infertility [2–5]. Secondly, scoliosis corresponds in reality to a complex three-dimensional (3D) deformity of the spine that simple two-dimensional (2D) radiographs are unable to assess precisely.
During the past decade, a new imaging technique based on George Charpak’s gaseous particle detector technology (Nobel Prize in Physics, 1992) has developed in order to solve these issues . Also known as the EOS imaging system (Biospace Imaging, Paris, France), this digital, biplanar, X-ray imaging acquisition system allows a quick assessment of the entire skeleton in a standing, weight-bearing, position with a significant decrease in radiation dose compared with conventional or other digital radiography systems [7–10]. It also creates 3D images of the skeleton by using computer models [6, 8, 10–15]. The EOS system is therefore particularly well-suited for diagnosis and monitoring of idiopathic scoliosis in children and adolescents [14, 16, 17], as well as leg-length discrepancy and misalignment , and for diagnosis and monitoring of degenerative conditions affecting the spine, hips and knees in adults . This pictorial review aims to familiarise radiologists with the EOS imaging system in evaluation of children and adolescents with idiopathic scoliosis.
EOS 2D/3D system
EOS 2D system
Using two orthogonal sources of radiation and linear detectors that are coupled together, the EOS system simultaneously produces two orthogonal X-ray images of the skeleton in the weight-bearing position. The child or the adolescent is standing upright (or sitting) in the centre of the device (i.e. at the intersection of the two X-ray fan beams) (Fig. 1). Gonadal shielding is usually not applied. Before scanning, the radiology technician defines the limits of the region of interest, in height and width, utilising to two laser beams. The exploration width of the device is limited to 50 cm (corresponding to a lateral diaphragm being wide open). Vertical scanning from head to pelvis for full spine imaging takes about 5–10 s, whereas scanning from head to toe for full body imaging takes about 15–20 s. Only AP or lateral views may also be acquired. If only frontal radiographs are required, a PA projection is used to lessen the radiation dose to the breasts and gonads. Parameters of acquisition (kilovoltage [kV] values, milliampere [mA] values and scanning speed) are variable, depending on the child’s age and weight. The radiology technician can thus choose from three presets: morphotype 1 (slim); 2 (normal) or 3 (corpulent). Acquisition parameters are about 80–90 kV and 200–250 mA for AP views; 100 kV and 250–320 mA for lateral views; scanning speed is chosen between 2 and 4 on the vendor-specific scale (ranging from 1, fast, to 8, slow). In practice, presets 1 and 2 are used for children (age, 5–12 years; weight about 30–45 kg) and adolescents (age, 13–18 years; weight about 45–70 kg) respectively; preset 3 is used only for obese adolescents (weight superior to 75 kg). Like for conventional or other digital radiography systems, child positioning is important to obtain reproducible, comparable radiographs. Among EOS system users, arm positioning is still subject to debate on lateral views because of the superimposition of both humeri on the spine and possible shift in sagittal spinal alignment. The best positioning would be elbows flexed with fists or fingers resting on clavicles or on the cheeks [19, 20]. In our experience, however, this position is not always easy to maintain; at our hospital, when both AP and lateral views are needed, children and adolescents are positioned with the arms supported in front of them, on a bar or on the device wall.
EOS 3D system
Simultaneous production of two orthogonal X-ray images allows the system to generate 3D images of the skeleton (i.e. the spine, the lower limbs or both) on a dedicated workstation (sterEOS), using key anatomical bony landmarks identified by an operator on the AP and lateral X-ray images, a large statistical database, shape recognition techniques and edge-detection algorithms. The mean reconstruction time is about 20–30 min for 3D spine rendering, 35–45 min for 3D spine and lower limb rendering. It may be much longer (>1 h) for patients with severe idiopathic scoliosis.
EOS system versus conventional radiography, other digital radiography systems and computed tomography
The EOS system differs from conventional radiography, other digital radiography systems and computed tomography (CT) in several regards: firstly, it allows for imaging in a standing position (or a sitting position with disabled children); secondly, it enables whole-body imaging (if necessary); thirdly, it reduces the radiation dose; fourthly, it creates 3D images of the skeleton.
AP and lateral X-ray images of the spine are acquired in a single vertical scanning mode. Therefore, in contrast to conventional radiography and other digital radiography systems, the EOS system cannot be used in young children with idiopathic infantile scoliosis who cannot stand in the device. In these children, AP and lateral images of the spine have to be performed supine using conventional or, much more frequently, digital radiographic equipment. The latter is now equipped with software that allows automatic stitching of separate cervical, thoracic and lumbar spine radiographs into a single final image. However, some limitations may also be encountered with these techniques (i.e. geometric distortion and stitching errors in conventional and digital imaging respectively) .
The EOS system can acquire X-ray images of the entire skeleton. This may be very useful for assessing relationships between the spine, the pelvis and the lower extremities in standing functional position (Fig. 2). In fact, significant leg length discrepancy may be responsible for pelvic obliquity and lumbar scoliosis . However, scanning from the base of the skull to the toes requires longer acquisition times; specific artefacts due to patient’s movement therefore may occur in children unable to stay still while performing scanning, resulting in distorted images (Fig. 3).
The EOS system allows a significant reduction of radiation dose, by a factor of 2.5–10 compared with 2D conventional radiography and other digital radiography systems [6, 7, 9, 10, 23] and by a factor of up to 800–1,000 compared with 3D CT reconstructions . In our experience, we found a dose reduced by a factor of 4 when comparing our EOS system (average dose area product or DAP of 23.6 mGy·cm2/kg ± 4.32) with our digital radiography system (average DAP of 95.7 mGy·cm2/kg ± 30.39) in children with idiopathic scoliosis requiring both AP and lateral views.
With the EOS system, the dose depends on kV and mA values, the chosen preset (1, 2 or 3), the scanning speed and the region of interest. For simultaneous AP and lateral radiographs of the spine, the total DAP is around 860 mGy·cm2 for morphotype 1 (child), around 1,180 mGy·cm2 for morphotype 2 (adolescent) and around 1,780 mGy·cm2 for morphotype 3 (obese adolescent). The radiation dose decreases when the translational speed of the X-ray tubes increases (but the image quality decreases as well). It also decreases when the fan-shaped beam of photons is laterally collimated.
Three-dimensional images of the skeleton
Idiopathic scoliosis is characterised by a vertebral deviation in the coronal and sagittal planes but also by a vertebral rotation in the axial (or horizontal) plane. Axial vertebral rotation is difficult to assess on 2D radiographs but it may be explored with CT scans and 3D CT reconstructions [24, 25]. This technique is, however, performed in the supine position; it is limited to short spinal segments and requires a higher radiation dose than conventional or digital radiography, even at low CT doses. In contrast, the EOS system provides large size 3D images of the spine (Fig. 4) from the two lowered-dose X-rays, with no additional radiation and in standing functional position. Three-dimensional EOS images differ from CT reconstructions in that they correspond to surface reconstructions (that are not validated yet in congenital scoliosis) and not real reconstructions. These 3D images provide a better understanding of the spinal deformity from different perspectives (Fig. 4). They may be performed with and without bracing (Fig. 5) or before and after surgery (Fig. 6). Once 3D images are complete, the software automatically generates measurements related to spinal coronal (Cobb angle) and sagittal curves (thoracic kyphosis, lumbar lordosis), and to pelvic parameters. Since they have been computed from 3D space, these measurements have been shown to be more accurate, reliable and reproducible [15, 26]. In current practice, however, some difficulties may be encountered during the 3D reconstruction process. A severe curvature in the coronal plane is responsible for poor visibility of some vertebrae in the sagittal plane, making the adjustment of the model by the operator more difficult (Fig. 7). The presence of lumbosacral transitional vertebrae (i.e. sacralisation of L5 or lumbarisation of S1) is another cause of difficulty since the sterEOS 3D software is not validated yet for this type of anatomical variant (Fig. 8). In this case, the best solution for the operator is to exclude the transitional vertebra from the 3D reconstruction process.
EOS 2D/3D system in the assessment of idiopathic scoliosis
EOS 2D system
It can be used to determine the usual spinal and pelvic radiographic parameters in both the coronal and sagittal planes (Table 1), and to assess skeletal maturity [27–34]. According to the Lenke classification system (Table 2), different types of scoliosis may be encountered (Figs. 4, 6, 7, 9 and 10). This classification takes into account the curve type in the coronal plane (structural curve versus non-structural curve[s]), its location (thoracic, lumbar or thoraco-lumbar), its flexibility, and the curves in the sagittal plane to guide surgical treatment of scoliosis . Therefore, it requires standing frontal and lateral spinal radiographs as well as rightward- and leftward-bending radiographs. The latter are useful to make the distinction between the structural curve (also called the primary or the major curve) and the non-structural curves (also called secondary curves or minor curves) before surgery. The structural curve is the largest curve, the one exhibiting more vertebral rotation and the least flexible one (i.e. the one that is non-correctable or partially correctable on ipsilateral sideward-bending with a Cobb angle ≥25°) . It is usually included in operative fusion. In contrast, the non-structural curves are the smallest curves, those exhibiting less vertebral rotation and the most flexible ones (i.e. the ones that are non-correctable or partially correctable on ipsilateral sideward-bending views with a Cobb angle <25°) .They develop secondarily, and are usually not included in operative fusion. Rightward- and leftward-bending radiographs are not currently validated in the EOS device, but they may be performed in positioning the patient off-centre within the system (Fig. 11).
EOS 3D system
It can be used to measure the degree of axial vertebral rotation. This is usually assessed semi-quantitatively on frontal radiographs by different methods, in which the spinous process location (Cobb)  or the pedicle location [37–39] are used as indirect indicators of the severity of axial vertebral rotation. In our institution, we prefer the Nash-Moe method (Fig. 12) or each time if possible, the direct assessment of axial vertebral rotation with the EOS system and its top view method (Fig. 13). This method shows the position and rotation of the apical vertebra in the horizontal plane based on the interacetabular distance (Fig. 13). More recently, via the concept of “vertebral vectors”, Illés et al. [17, 40] found another way to visualise the position of all vertebrae, including the apical one, in the horizontal plane and, most importantly, to quantify the vertebral rotation in all three planes simultaneously (Fig. 13). This may be used to show the evolution of scoliosis before and after surgery (Fig. 14).
In conclusion, radiography plays a pivotal role in the evaluation of children and adolescents with idiopathic scoliosis. However, it is limited to 2D measurements of frontal and sagittal spinal curves, and regular follow-up until skeletal maturity requires repeated X-ray exposure. The EOS 2D/3D system is a biplanar X-ray system that appeared in 2005 to overcome these drawbacks. It allows imaging of the spine at lowered radiation levels. Another advantage is the possibility of obtaining 3D images of the spine in the standing functional position. This new imaging technique is therefore increasingly being used in paediatric imaging departments. In the present article we have provided an overview of the potential usefulness of the EOS 2D/3D system in children and adolescents with idiopathic scoliosis; however, it appears too early to assess precisely its 3D ability and its impact on therapeutic management.
Kim H, Kim HS, Moon ES, Yoon CS, Chung TS, Song HT et al (2010) Scoliosis imaging: what radiologists should know. Radiographics 30:1823–1842
Nash CL Jr, Gregg EC, Brown RH, Pillai K (1979) Risks of exposure to X-rays in patients undergoing long-term treatment for scoliosis. J Bone Joint Surg Am 61:371–374
Hoffman DA, Lonstein JE, Morin MM, Visscher W, Harris BS 3rd, Boice JD Jr (1989) Breast cancer in women with scoliosis exposed to multiple diagnostic x rays. J Natl Cancer Inst 81:1307–1312
Ronckers CM, Land CE, Miller JS, Stovall M, Lonstein JE, Doody MM (2010) Cancer mortality among women frequently exposed to radiographic examinations for spinal disorders. Radiat Res 174:83–90
Goldberg MS, Mayo NE, Levy AR, Scott SC, Poîtras B (1998) Adverse reproductive outcomes among women exposed to low levels of ionizing radiation from diagnostic radiography for adolescent idiopathic scoliosis. Epidemiology 9:271–278
Dubousset J, Charpak G, Dorion I, Skalli W, Lavaste F, Deguise J et al (2005) A new 2D and 3D imaging approach to musculoskeletal physiology and pathology with low-dose radiation and the standing position: the EOS system. Bull Acad Natl Med 189:287–297
Deschênes S, Charron G, Beaudoin G, Labelle H, Dubois J, Miron MC et al (2010) Diagnostic imaging of spinal deformities: reducing patients radiation dose with a new slot-scanning X-ray imager. Spine 35:989–994
McKenna C, Wade R, Faria R, Yang H, Stirk L, Gummerson N et al (2012) EOS 2D/3D X-ray imaging system: a systematic review and economic evaluation. Health Technol Assess 16:1–188
Gheno R, Nectoux E, Herbaux B, Baldisserotto M, Glock L, Cotten A et al (2012) Three-dimensional measurements of the lower extremity in children and adolescents using a LDBX-ray device. Eur Radiol 22:765–771
Dubousset J, Charpak G, Skalli W, Kalifa G, Lazennec JY (2007) EOS stereo-radiography system: whole-body simultaneous anteroposterior and lateral radiographs with very low radiation dose. Rev Chir Orthop Reparatrice Appar Mot 93:141–143
Aubin CE, Dansereau J, Parent F, Labelle H, de Guise JA (1997) Morphometric evaluations of personalised 3D reconstructions and geometric models of the human spine. Med Biol Eng Comput 35:611–618
Dumas R, Aissaoui R, Mitton D, Skalli W, de Guise JA (2005) Personalized body segment parameters from biplanar low-dose radiography. IEEE Trans Biomed Eng 52:1756–1763
Baudoin A, Skalli W, de Guise JA, Mitton D (2008) Parametric subject-specific model for in vivo 3D reconstruction using bi-planar X-rays: application to the upper femoral extremity. Med Biol Eng Comput 46:799–805
Humbert L, De Guise JA, Aubert B, Godbout B, Skalli W (2009) 3D reconstruction of the spine from biplanar X-rays using parametric models based on transversal and longitudinal inferences. Med Eng Phys 31:681–687
Glaser DA, Doan J, Newton PO (2012) Comparison of 3D spinal reconstruction accuracy: biplanar radiographs with EOS versus computed tomography. Spine 37:1391–1397
Ilharreborde B, Steffen JS, Nectoux E, Vital JM, Mazda K, Skalli W et al (2011) Angle measurement reproducibility using EOS three-dimensional reconstructions in adolescent idiopathic scoliosis treated by posterior instrumentation. Spine 36:1306–1313
Illés T, Tunyogi-Csapó M, Somoskeöy S (2011) Breakthrough in three-dimensional scoliosis diagnosis: significance of horizontal plane view and vertebra vectors. Eur Spine J 20:135–143
Than P, Szuper K, Somoskeöy S, Warta V, Illlés T (2012) Geometrical values of the normal and arthritic hip and knee detected with the EOS imaging system. Int Orthop 36:1291–1297
Faro FD, Marks MC, Pawelek J, Newton PO (2004) Evaluation of a functional position for lateral radiograph acquisition in adolescent idiopathic scoliosis. Spine 29:2284–2289
Morvan G, Mathieu P, Vuillemin V, Guerini H, Bossard P, Zeitoun F et al (2011) Standardized way for imaging of the sagittal spinal balance. Eur Spine J 20(Suppl 5):602
Supakul N, Newbrough K, Cohen MD, Jennings SG (2012) Diagnostic errors from digital stitching of scoliosis images—the importance of evaluating the source images prior to making a final diagnosis. Pediatr Radiol 42:584–598
Raczkowski JW, Daniszewska B, Zolynski K (2010) Functional scoliosis caused by leg length discrepancy. Arch Med Sci 6:393–398
Dietrich TJ, Pfirrmann CW, Schwab A, Pankalla K, Buck FM (2013) Comparison of radiation dose, workflow, patient comfort and financial break-even of standard digital radiography and a novel biplanar low-dose X-ray system for upright full-length lower limb and whole spine radiography. Skelet Radiol 42:959–967
Aaro S, Dahlborn M (1981) Estimation of vertebral rotation and the spinal and rib cage deformity in scoliosis by computer tomography. Spine 6:460–467
Ho EK, Upadhyay SS, Ferris L, Chan FL, Bacon-Shone J, Hsu LC et al (1992) A comparative study of computed tomographic and plain radiographic methods to measure vertebral rotation in adolescent idiopathic scoliosis. Spine 17:771–774
Somoskeöy S, Tunyogi-Csapo M, Bogyo C, Illés T (2012) Accuracy and reliability of coronal and sagittal spinal curvature data based on patient-specific three-dimensional models created by the EOS 2D/3D imaging system. Spine J 12:1052–1059
Mac-Thiong JM, Labelle H, Berthonnaud E, Betz RR, Roussouly P (2007) Sagittal spinopelvic balance in normal children and adolescents. Eur Spine J 16:227–234
Vidal C, Ilharreborde B, Azoulay R, Sebag G, Mazda K (2013) Reliability of cervical lordosis and global sagittal spinal balance measurements in adolescent idiopathic scoliosis. Eur Spine J 22:1362–1367
Roussouly P, Nnadi C (2010) Sagittal plane deformity: an overview of interpretation and management. Eur Spine J 19:1824–1836
Legaye J, Duval-Beaupère G, Hecquet J, Marty C (1998) Pelvic incidence: a fundamental pelvic parameter for three-dimensional regulation of spinal sagittal curves. Eur Spine J 7:99–103
Legaye J (2007) The femoro-sacral posterior angle: an anatomical sagittal pelvic parameter usable with dome-shaped sacrum. Eur Spine J 16:219–225
Stagnara P, De Mauroy JC, Dran G, Gonon GP, Costanzo G, Dimnet J et al (1982) Reciprocal angulation of vertebral bodies in a sagittal plane: approach to references for the evaluation of kyphosis and lordosis. Spine 7:335–342
Roussouly P, Berthonnaud E, Dimnet J (2003) Geometrical and mechanical analysis of lumbar lordosis in an asymptomatic population: proposed classification. Rev Chir Orthop Reparatrice Appar Mot 89:632–639
Tan KJ, Moe MM, Vaithinathan R, Wong HK (2009) Curve progression in idiopathic scoliosis: follow-up study to skeletal maturity. Spine 34:697–700
Lenke LG, Betz RR, Harms J, Bridwell KH, Clements DH, Lowe TG et al (2001) Adolescent idiopathic scoliosis: a new classification to determine extent of spinal arthrodesis. J Bone Joint Surg Am 83:1169–1181
Cobb JR (1948) Outline for the study of scoliosis. Instructional Course Lectures. Am Acad Orthop Surg 5:261–275
Perdriolle R, Vidal J (1985) Thoracic idiopathic scoliosis curve evaluation and prognosis. Spine 20:546–553
Nash C, Moe JH (1969) A study of vertebral rotation. J Bone Joint Surg 51:223–229
Drerup B (1984) Principles of measurement of vertebral rotation from frontal projection of the pedicles. J Biomech 17:923–935
Illés T, Somoskeöy S (2013) Comparison of scoliosis measurements based on three-dimensional vertebra vectors and conventional two-dimensional measurements: advantages in evaluation of prognosis and surgical results. Eur Spine J 22:1255–1263
The authors would like to thank Aymeric FREMEAUX for the surface 3D reconstructions of the spine.
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Amzallag-Bellenger, E., Uyttenhove, F., Nectoux, É. et al. Idiopathic scoliosis in children and adolescents: assessment with a biplanar X-ray device. Insights Imaging 5, 571–583 (2014). https://doi.org/10.1007/s13244-014-0354-0