Date Published: February 2, 2017
Publisher: Public Library of Science
Author(s): Johannes Rehm, Thomas Germann, Michael Akbar, Wojciech Pepke, Hans-Ulrich Kauczor, Marc-André Weber, Daniel Spira, Chun Kee Chung.
To retrospectively assess the interreader reproducibility and reliability of EOS 3D full spine reconstructions in patients with adolescent idiopathic scoliosis (AIS).
73 patients with mean age of 17 years and a moderate AIS (median Cobb Angle 18.2°) obtained low-dose standing biplanar radiographs with EOS. Two independent readers performed “full spine” 3D reconstructions of the spine with the “full-spine” method adjusting the bone contour of every thoracic and lumbar vertebra (Th1-L5). Interreader reproducibility was assessed regarding rotation of every single vertebra in the coronal (i.e. frontal), sagittal (i.e. lateral), and axial plane, T1/T12 kyphosis, T4/T12 kyphosis, L1/L5 lordosis, L1/S1 lordosis and pelvic parameters. Radiation exposure, scan-time and 3D reconstruction time were recorded.
Interclass correlation (ICC) ranged between 0.83 and 0.98 for frontal vertebral rotation, between 0.94 and 0.99 for lateral vertebral rotation and between 0.51 and 0.88 for axial vertebral rotation. ICC was 0.92 for T1/T12 kyphosis, 0.95 for T4/T12 kyphosis, 0.90 for L1/L5 lordosis, 0.85 for L1/S1 lordosis, 0.97 for pelvic incidence, 0.96 for sacral slope, 0.98 for sagittal pelvic tilt and 0.94 for lateral pelvic tilt. The mean time for reconstruction was 14.9 minutes (reader 1: 14.6 minutes, reader 2: 15.2 minutes, p<0.0001). The mean total absorbed dose was 593.4μGy ±212.3 per patient. EOS “full spine” 3D angle measurement of vertebral rotation proved to be reliable and was performed in an acceptable reconstruction time. Interreader reproducibility of axial rotation was limited to some degree in the upper and middle thoracic spine due the obtuse angulation of the pedicles and the processi spinosi in the frontal view somewhat complicating their delineation.
The advantages of three-dimensionally analyzing and quantifying adolescent idiopathic scoliosis (AIS) for follow-up and therapy planning are well known [1–2]. Apart from the clinical examination, regular roentgenologic monitoring with two plane radiographs are the gold standard and are fundamental to detect progress and estimate the prognosis. In addition X-rays serve as pre- and postoperative assessment tools in case of spondylodesis. Although modern techniques have been able to reduce radiation exposure, ionizing radiation of conventional plane radiographs was extrapolated to increase the lifetime risk of developing breast and thyroid cancer by 1–2%, especially in young patients with AIS [3–4]. Two-dimensional images are limited in their ability to assess vertebral rotation and pelvic parameters, which is why an additional CT is sometimes needed to increase accuracy of measurements. Besides radiation exposure the main disadvantage of the CT is the supine positioning of the patient during the examination, which can lead to considerable differences in vertebral rotation and extent of scoliosis when compared to upright posture. The new EOS-technology (EOS imaging, Paris, France) based on a low-dose X-ray system allows 3D modeling of the spine based on 2-dimensional X-rays acquired in an upright position providing information about scoliosis and sagittal balance. In addition, it provides information about pelvic parameters. The core of the EOS system is a multiwire proportional chamber with two independent two independent X-ray tubes producing a 45-cm-wide X-ray beam and image acquisition plates complete the system . The X-ray system surrounds the chamber the patient stands within and scans the patient longitudinally in a weight-bearing position over a preset area. The sterEOS (EOS imaging, Paris, France) software enables 3D modeling of the bone envelope based on anatomic references defined by the reader and providing specific clinical parameters [6–7]. Although EOS is sometimes equated with CT due to its ability to provide 3D reconstructions, it does not provide information on soft tissues. In recent studies the validity of EOS imaging in a preoperative and postoperative setting as well as in the follow up of patients with AIS has been investigated. The EOS images were found to be superior or equivalent to conventional radiographs in terms of global image quality and structure visibility with up to nine times lower radiation [8–10].
The limitations of 2D measurements based on two-plane X-rays and the advantages of measurements obtained from 3D reconstructions have been emphasized in former studies [14–16]. Apart from the Cobb-angle, the vertebral rotation is an important clinical parameter in the follow-up and the preoperative planning in patients with AIS. One disadvantage of CT which is able to provide accurate 3D measurements is its higher radiation exposure. The results of the radiation exposure analysis in this study show that the absorbed dose is 26 times lower with EOS compared to a full-spine CT and about 8 times lower than full-spine low-dose CT (Table 7).