Geometric Structure of 3D Spinal Curves: Plane Regions and Connecting Zones

Three-dimensional reconstructions of Lenke 1A curves

Background

Scoliosis is a 3D deformity that can be reconstructed through 2D antero-posterior and lateral radiographs, which provide an upper view of the deformed spine as well as regional planes matching all vertebrae of elective plane for each curve. The objective of this study is to explore whether all idiopathic scoliosis classified Lenke 1A have the same 3D representation made with regional planes.

Methods

All patients treated for idiopathic thoracic scoliosis during the growth period and classified Lenke 1A were included in this study conducted in the pediatric spinal orthopedic department of Centre des Massues. A photogrammetric technique was used to obtain a 3D reconstruction, from regional planes identified on radiographs made with the EOS system. Three regional planes are usually identified in asymptomatic spines: lumbar, dorsal, and cervical—none of them presenting rotation. In the studied group, the number of planes, the rotation, and the limit vertebrae of each plane were looked for.

Results

Sixty-three patients were included (47 girls and 16 boys, mean age 11.3 years). The Cobb angle was meanly 36.5°. The scoliosis was reconstructed with three regional planes (57%) or four ones (43%, with the thoracic plane divided into two planes). Maximal rotation was found in the thoracic plane, especially when scoliosis was represented with four regional planes. The transition between planes 2 and 3 was mainly located between the fourth and sixth dorsal vertebrae.

Conclusion

The use of an arbitrary regional plane representation of a 3D shape leads to conclude that there are two types of Lenke 1A scoliosis, which should be taken into account for designing the brace.

The use of a photogrammetric method for the three-dimensional evaluation of spinal correction in scoliosis

PURPOSE

Clinical parameters, characterizing the spinal deformations due to scoliosis, are still directly measured on the spinal curve plane projections.

METHODS

A 3D spinal curve has been reconstructed from its two projections, using photogrammetric techniques. Each spinal curve is a compound of several plane regions, where it is purely flexed, and short zones of connection, where abduction and axial rotation components are concentrated. All spinal curves are represented as linear chains of regional planes articulated together. The regional plane is represented by a triangle, where one summit corresponds to the point of maximum offset. The set of weight forces, representing pelvis and spine, forms a bundle of vertical forces. The dispersion of the bundle illustrates the postural stability of patients.

RESULTS AND CONCLUSIONS

The first objective was to numerically describe the changes of the 3D spinal feature, due to the correcting treatment. Changes are calculated from the comparison between 3D radiologic situations, between before and after treatment. The second objective was to determine the direction of the external force, which would be the most efficient for correcting the patient set spine/rib cage. A mild mechanical analysis is proposed, for representing the transit of the external force, from rib cage to thoracic regional plane.