Axial plane characteristics of thoracic scoliosis and their usefulness for determining the fusion levels and the correction technique.

PURPOSE: There is insufficient information regarding axial plane characteristics of scoliosis despite its 3D nature. The posterior-anterior vertebral vector (VV) has been proposed to characterize the axial plane appearances of the thoracic scoliosis. This study aimed to highlight the importance of knowledge of axial plane features when determining fusion levels and correction techniques of thoracic curves. METHODS: Altogether, 233 thoracic curves were analyzed using the VV after proving its usability instead of 3D angles to determine axial plane parameters such as apical vertebral (APV) axial rotations, APV lateral displacement, and intervertebral rotations (IVR). K-means clustering and regression analysis were used to identify axial plane curve patterns and determine the relationship between the coronal angles and axial plane characteristics, respectively. RESULTS: A close correlation was found between 3D angles and VV projected angles. Eight axial plane clusters were distinct, exhibiting different lateral APV displacement toward the interacetabular axis with relatively small axial rotations and a simultaneous decrease in sagittal curves. The regression analysis showed that the correlation of coronal curve magnitude was significantly stronger (r = 0.78) with APV lateral translation than with APV axial rotation (r = 0.65). CONCLUSION: Based on these findings, the primary goal of scoliosis correction should focus on minimizing lateral translation rather than eliminating axial rotation. Knowing the IVR in the axial plane helps accurately determine the limits of the structural curves. VV-based axial views can facilitate the accurate determination of the end vertebrae and selection of the appropriate correction technique of the curve. These slides can be retrieved under Electronic Supplementary Material.

Axial plane dissimilarities of two identical Lenke-type 6C scoliosis cases visualized and analyzed by vertebral vectors.

PURPOSE: The global appearance of scoliosis in the horizontal plane is not really known. Therefore, the aims of this study were to analyze scoliosis in the horizontal plane using vertebral vectors in two patients classified with the same Lenke group, and to highlight the importance of the information obtained from these vertebral vector-based top-view images in clinical practice. METHODS: Two identical cases of scoliosis were selected, based on preoperative full-body standing anteroposterior and lateral radiographs obtained by the EOS™ 2D/3D system. Three-dimensional (3D) surface reconstructions of the spinal curves were performed by using sterEOS™ 3D software before and after surgery. In both patients, we also determined the vertebral vectors and horizontal plane coordinates for analyzing the curves mathematically before and after surgery. RESULTS: Despite the identical appearance of spinal curves in the frontal and sagittal planes, the horizontal views seemed to be significantly different. The vertebral vectors in the horizontal plane provided different types of parameters regarding scoliosis and the impact of surgical treatment: reducing lateral deviations, achieving harmony of the curves in the sagittal plane, and reducing rotations in the horizontal plane. CONCLUSIONS: Vertebral vectors allow the evolution of scoliosis curve projections in the horizontal plane before and after surgical treatment, along with representation of the entire spine. The top view in the horizontal plane is essential to completely evaluate the scoliosis curves, because, despite the similar representations in the frontal and sagittal planes, the occurrence of scoliosis in the horizontal plane can be completely different. These slides can be retrieved under Electronic Supplementary Material.

The horizontal plane appearances of scoliosis: what information can be obtained from top-view images?

PURPOSE: A posterior-anterior vertebral vector is proposed to facilitate visualization and understanding of scoliosis. The aim of this study was to highlight the interest of using vertebral vectors, especially in the horizontal plane, in clinical practice. METHODS: We used an EOS two-/three-dimensional (2D/3D) system and its sterEOS 3D software for 3D reconstruction of 139 normal and 814 scoliotic spines-of which 95 cases were analyzed pre-operatively and post-operatively, as well. Vertebral vectors were generated for each case. Vertebral vectors have starting points in the middle of the interpedicular segment, while they are parallel to the upper plate, ending in the middle of the segment joining the anterior end plates points, thus defining the posterior-anterior axis of vertebrae. To illustrate what information could be obtained from vertebral vector-based top-view images, representative cases of a normal spine and a thoracic scoliosis are presented. RESULTS: For a normal spine, vector projections in the transverse plane are aligned with the posterior-anterior anatomical axis. For a scoliotic spine, vector projections in the horizontal plane provide information on the lateral decompensation of the spine and the lateral displacement of vertebrae. In the horizontal plane view, vertebral rotation and projections of the sagittal curves can also be analyzed simultaneously. CONCLUSIONS: The use of posterior-anterior vertebral vector facilitates the understanding of the 3D nature of scoliosis. The approach used is simple. These results are sufficient for a first visual analysis furnishing significant clinical information in all three anatomical planes. This visualization represents a reasonable compromise between mathematical purity and practical use.

The third dimension of scoliosis: The forgotten axial plane.

Idiopathic scoliosis is a three-dimensional (3D) deformity of the spine. In clinical practice, however, the diagnosis and treatment of scoliosis consider only two dimensions (2D) as they rely solely on postero-anterior (PA) and lateral radiographs. Thus, the projections of the deformity are evaluated in only the coronal and sagittal planes, whereas those in the axial plane are disregarded, precluding an accurate assessment of the 3D deformity. A universal dogma in engineering is that designing a 3D object requires drawing projections of the object in all three planes. Similarly, when dealing with a 3D deformity, knowledge of the abnormalities in all three planes is crucial, as each plane is as important as the other two planes. This article reviews the chronological development of axial plane imaging and spinal deformity measurement.

Sagittal plane correction in idiopathic scoliosis.

STUDY DESIGN: Patients with idiopathic scoliosis who had undergone posterior fusion by means of posterior multisegmented hook instrumentation were studied retrospectively. OBJECTIVES: To present the changes in projected thoracic hypokyphosis and the behavior of lumbar lordosis within and below the fusion. SUMMARY OF BACKGROUND DATA: Scoliosis is a three-dimensional deformity of the spine. The idiopathic cases usually exhibit a flattening of the sagittal curves, which had further deteriorated when the Harrington technique was used. The consequences included the flat back, angular increase of the lumbar lordosis below the fusion, and low back pain. Previous studies showed no or only moderate correction of thoracic hypokyphosis when using Cotrel-Dubousset instrumentation or its modifications were used. Harrington rod systems resulted in decreased lumbar lordosis in the fusion area and increased lordosis below the fusion. No background data were found concerning the effects of multisegmented hook instrumentation on the lumbar spine within and below the fusion. METHODS: For this study, 306 patients with idiopathic scoliosis who had undergone posterior spinal fusion with multisegmented hook systems using the derotation maneuver were analyzed after a mean follow-up period of 5 years and 4 months. The coronal plane curvature, the sagittal plane projection of the thoracic kyphosis, and the lumbar lordosis within and below the fusion were evaluated. RESULTS: The average coronal plane correction was 67.1%. Analysis of the sagittal contours demonstrated that the preoperative thoracic hypokyphosis (less than 20 degrees between T4 and T12) increased by an average of 12 degrees, and that 55.1% of hypokyphotic backs were corrected to the normal range (20 degrees to 40 degrees ). In patients with frank lordosis (kyphosis less than 10 degrees ), the degree of correction was higher (average, 16 degrees ), but complete correction was achieved in only 38.5% of the cases. In patients with mild lordosis (kyphosis between 10 degrees and 20 degrees ), the average correction was 8 degrees, and 71.3% of the patients were in the normal range after surgery. The normal preoperative thoracic kyphosis was preserved in 81.3% of the cases. In the lumbar area, the Cotrel-Dubousset instrumentation was capable of correcting the preoperative hypolordosis (less than -20 degrees between L1 and L5) in 94.4% of the cases. The normal preoperative lordosis (-20 degrees to -60 degrees ) was preserved in 97.9% of the cases. The hyperlordosis was corrected in all cases. Analysis of the data in terms of lower fusion limit showed that the lower the caudal hook, the greater the increase in the segmental lordosis within the fusion, without any increase distal to the fusion. No segmental hyperlordosis was observed below the fusion. CONCLUSIONS: The Cotrel-Dubousset technique ensures considerable sagittal correction of the spine. In the course of scoliosis correction, it is possible to preserve the normal preoperative sagittal profile of the spine, to correct the slightly flattened thoracic kyphosis, to increase materially the kyphosis of the frankly hypokyphotic spine, to preserve or restore normal lumbar lordosis in a considerable percentage of the cases, to avoid angular segmental hyperlordosis at the level of the first disc below the fusion, and to avoid retrolisthesis of the last fused vertebra.

Hyperrotatory paradoxic kyphosis.

STUDY DESIGN: A retrospective radiographic evaluation of 32 patients with hyperrotatory scoliosis accompanied by paradoxic hyperkyphosis, who were treated with posterior multilevel hook instrumentation. OBJECTIVES: To give a three-dimensional analysis of this particular deformity and to evaluate the coronal, sagittal, and horizontal plane corrections in these specific curves. SUMMARY OF BACKGROUND DATA: Lordoscoliosis with a severe rotational component produces paradoxic kyphosis in the sagittal plane. A vertebral derotational maneuver is essential to restore the normal sagittal alignment. METHODS: Thirty-two patients were treated with posterior multilevel hook instrumentation. Nine patients had previously undergone anterior release and fusion. The derotational maneuver could be accomplished in 21 cases. The coronal Cobb angle and the extents of apical vertebral rotation, sagittal hyperkyphosis, upper and lower compensatory lordosis, and sagittal trunk balance were measured after an average follow-up period of 5 years and 9 months. RESULTS: The mean coronal deformity decreased from 89.9 degrees before surgery to 40.7 degrees. The mean preoperative hyperkyphosis was 70.9 degrees in the thoracic spine, 45.9 degrees in the thoracolumbar spine, and 55 degrees in the lumbar region. These values were reduced to 39.7 degrees, 6.8 degrees, and -15 degrees, respectively. The lateral spinal balance changed from -21.3 mm to -8.5 mm. The average rotational correction measured by the method of Jackson was 51% before surgery and 39% after surgery (correction: 23.5%). There was a positive correlation between the preoperative kyphosis angle and the apical rotation (r = 0.58) and between the decrease of kyphosis and the correction of the rotation (r = 0.67) in cases when the derotational maneuver could be accomplished. CONCLUSIONS: If the apex of the scoliosis and the kyphosis are on the same level, the vertebral hyperrotation is responsible for the sagittal malalignment. Satisfactory results can be achieved with posterior multilevel hook instrumentation.