[Effect of morphological changes in the sagittal plane of vertebrae and discs on degenerative kyphodeformity]

To explore the effects of morphological changes such as vertebral wedge deformation and disc degeneration (collapse) on adult thoracolumbar/lumbar degenerative kyphosis(TL/LDK) deformity.

A retrospective analysis of 32 patients with spinal TL/LDK deformity admitted from August 2015 to December 2020, including 8 males and 24 females, aged 48 to 75(60.3±12.4) years old. On the long-cassette standing upright lateral radiographs, the coronal Cobb angle, sagittal thoracic lumbar/lumbar kyphosis angle(KA) of spine were measured, and the height and wedge parameters of apex vertebral(AV) and two vertebrae(AV-1, AV-2, AV+1, AV+2) above and below AV and the intervertebrae and the intervertebral disc(AV-1D, AV-2D, AV+1D, AV+2D) were evaluated, involving anterior vertebral body height(AVH), posterior vertebral body height(PVH), vertebral wedge angle(VWA), ratio of vertebral wedging(RVW), anterior disc height(ADH), posterior disc height(PDH), disc wedge angle(DWA), ratio of disc wedging(RDW), and DWA/KA.

The average angle of kyphosis was (44.2±19.1)°. A significant decrease in anterior height of vertebral was observed compared to the posterior height of vertebral(P<0.005). There was no significant difference in anterior and posterior height of discs. The vertebral wedging ratio/contribution ratio:AV-2(14.98±10.95)%/(14.21±8.08)%, AV-1(21.08±12.39)%/(18.09±7.38)%, AV(26.94±11.94)%/(25.52±8.64)%, AV+1(24.19±8.42)%/(20.82±8.69)%, AV+2(20.56±7.80)%/(15.60±9.71)%, total contribution(94.23±22.25)%, the disc wedging ratio/contribution ratio:AV-2D(2.88±2.57)%/(5.27±4.11)%, AV-1D(1.98±1.41)%/(2.29±2.16)%, AV+1D(-5.54±3.75)%/(-0.57±0.46)%, AV+2D(-8.27±4.62)%/(-1.22±1.11)%, total contribution (5.77±4.79)%. And the contribution rate of AV was significantly higher than that of adjacent vertebral(P<0.05).

The vertebral body and intervertebral disc shape both have influence on thoracolumbar kyphosis. However, the contribution of vertebral morphometry to the angle of TL/LDK deformity is relatively more important than the disc. The contribution of the wedge change of the AV to the TL/LDK deformity is particularly significant.