Upright, prone, and supine spinal morphology and alignment in adolescent idiopathic scoliosis

Abstract

Background: Patients with adolescent idiopathic scoliosis (AIS) are usually investigated by serial imaging studies during the course of treatment, some imaging involves ionizing radiation, and the radiation doses are cumulative. Few studies have addressed the correlation of spinal deformity captured by these different imaging modalities, for which patient positioning are different. To the best of our knowledge, this is the first study to compare the coronal, axial, and sagittal morphology of the scoliotic spine in three different body positions (upright, prone, and supine) and between three different imaging modalities (X-ray, CT, and MRI).

Methods: Sixty-two AIS patients scheduled for scoliosis surgery, and having undergone standard pre-operative work-up, were included. This work-up included upright full-spine radiographs, supine bending radiographs, supine MRI, and prone CT as is the routine in one of our institutions. In all three positions, Cobb angles, thoracic kyphosis (TK), lumbar lordosis (LL), and vertebral rotation were determined. The relationship among three positions (upright X-ray, prone CT, and supine MRI) was investigated according to the Bland-Altman test, whereas the correlation was described by the intraclass correlation coefficient (ICC).

Results: Thoracic and lumbar Cobb angles correlated significantly between conventional radiographs (68° ± 15° and 44° ± 17°), prone CT (54° ± 15° and 33° ± 15°), and supine MRI (57° ± 14° and 35° ± 16°; ICC ≥0.96; P < 0.001). The thoracic and lumbar apical vertebral rotation showed a good correlation among three positions (upright, 22° ± 12° and 11° ± 13°; prone, 20° ± 9° and 8° ± 11°; supine, 16° ± 11° and 6° ± 14°; ICC ≥0.82; P < 0.001). The TK and LL correlated well among three different positions (TK 26° ± 11°, 22° ± 12°, and 17° ± 10°; P ≤ 0.004; LL 49° ± 12°, 45° ± 11°, and 44° ± 12°; P < 0.006; ICC 0.87 and 0.85).

Conclusions: Although there is a generalized underestimation of morphological parameters of the scoliotic deformity in the supine and prone positions as compared to the upright position, a significant correlation of these parameters is still evident among different body positions by different imaging modalities. Findings of this study suggest that severity of scoliotic deformity in AIS patients can be largely represented by different imaging modalities despite the difference in body positioning.

Keywords: Adolescent idiopathic scoliosis; Body positioning; Computed tomography; Magnetic resonance imaging; Three-dimensional morphology; Upright radiographs.

Fig. 1

On the MRI and CT images, the main thoracic and (thoraco)lumbar Cobb angle, thoracic kyphosis, and lumbar lordosis were measured using the same technique as for the conventional radiographs on the image where the curve and endplates were best visible by using the multiplanar reconstruction (MPR, a) for the MRI and the digitally reconstructed radiograph (b) for the CT scan. c The conventional X-ray

Fig. 2

The orientation of the upper and lower endplates of each individual vertebra of the computed tomography scans was determined by using the semi-automatic software, correcting for coronal and sagittal (a and b) tilt, to reconstruct the true transverse sections. The observer drew a contour around the vertebral body (yellow line in c) and spinal canal (blue line in c). The software calculated a center of gravity of the vertebral body (yellow dot in c) and spinal canal (blue dot in c). For each endplate, its longitudinal axis was calculated as the line between those two points (purple line in c). The rotation of this axis minus the rotation of the neutral sacral plate represents the rotation of the endplate

Fig. 3

In these scatterplots, the relation between thoracic Cobb angle in the upright, prone (red trend line), and supine (blue trend line) positions is shown. Although the upright Cobb angle was significantly larger, significant linear correlations were found (ICC 0.967; P < 0.001), indicating that with increasing Cobb angle, differences between the body positions increased simultaneously