The Height-Width-Depth Ratios of the Intervertebral Discs and Vertebral Bodies in Adolescent Idiopathic Scoliosis vs Controls in a Chinese Population

Abstract

Adolescent idiopathic scoliosis (AIS) patients have been reported to be taller and more slender than normal controls, suggesting less mechanical stiffness of their trunk and spine. For assessment of mechanical stiffness, to our best knowledge this is the first to study height-width-depth relations at the level of the individual vertebra and disc in 3-D and to evaluate its relation with the Cobb angle severity. A unique series of high-resolution pre-operative computed tomographic (CT) scans of a total of 105 Chinese patients with moderate to severe AIS and 11 age-matched non-scoliotic controls were used for this study. It was found that some geometric relations differed between primary thoracic curves, secondary curves and normal controls at the individual affected vertebra and disc level. The scoliotic discs in the primary curves were relatively more slender (taller and thinner) than in secondary curves and as compared to controls. In the lumbar spinal area, the vertebral bodies were more slender in the primary as well as secondary AIS curves as compared to the controls. Therefore, if all material properties remain the same, our finding indicates that scoliotic spines may be mechanically less stiff than normal spines. No significant correlation between any of the measures and Cobb angle severity was found.

3D Deformation Patterns of S Shaped Elastic Rods as a Pathogenesis Model for Spinal Deformity in Adolescent Idiopathic Scoliosis

“…shear and make the spine less stable 22 . The current analysis showed, in an elastic rod, without considering the differences in the spinal components (discs, vertebrae) 36,38 and without generalizing the vertebral alignment 37 , and under the same external loadings, some sagittal subtypes do not twist and deform in only one plane (Fig. 6A) whereas other sagittal curve types are prone to scoliotic-like 3D deformation with one or two twists in the spine (Fig.…”

“…Several biomechanical factors have been related to the mechanism of the spinal deformity development in AIS. Slender vertebrae and discs in AIS patients, compared to the non-scoliotic age-matched adolescents, is believed to increase the spinal flexibility and lead to spinal deformity in AIS 36 . The sagittal profile in AIS patients was reported to be more posteriorly inclined which increases the posteriorly directed shear force in AIS compared to the age-matched non-scoliotic adolescents contributing to the spinal instbility 37 .…”

“…The fundamentals of these deformations are explained analytically using Kirchhoff’s theory of elastic rods 44,45 . In analytical examination of the spinal deformity in AIS, mechanical phenomenon such as 2D buckling of the rods have been used to explain the mechanics of spinal deformation previously 36,38,46–53 . However, considering the 3D deformation of the spine in AIS, the mechanics of 2D buckling fails to explain essential aspects of the curve progression.…”

Idiopathic Scoliosis as a Rotatory Decompensation of the Spine

“…1. the fast longitudinal bone growth at the onset of curve development and the reported slenderness of the spine in adolescent idiopathic scoliosis (AIS) patients, with a natural sagittal curvature, which satisfy the requirement of the equations for a thin rod where the rod diameter is orders of magnitude smaller than the length of the rod; (59) 2. a decrease in axial support of the spine due to rapid changes in the height, weight, and moment arm, and additional laxity due to hormonal changes around puberty that add to flexibility; (60,61) 3. the loading patterns of the spine that can be considered as bending resulting from gravity and an axial torsion representing a shift in the position of the center of mass around puberty. (22) Relying on these assumptions, in a recent study, Pasha developed finite element (FE) models of the curved elastic rods with different geometries of their sagittal curvature.…”

Difference of Sagittal Alignment between Adolescents with Symptomatic Lumbar Isthmic Spondylolisthesis and the General Population

“…In adults, several studies have investigated the sagittal alignment in different populations 9 . Sagittal spine alignment was associated with Health-related quality of life (HRQoL) 10 , especially in elderly individuals 11 , 12 .…”