Three-dimensional vertebral wedging in mild and moderate adolescent idiopathic scoliosis

Abstract

Background: Vertebral wedging is associated with spinal deformity progression in adolescent idiopathic scoliosis. Reporting frontal and sagittal wedging separately could be misleading since these are projected values of a single three-dimensional deformation of the vertebral body. The objectives of this study were to determine if three-dimensional vertebral body wedging is present in mild scoliosis and if there are a preferential vertebral level, position and plane of deformation with increasing scoliotic severity.

Methodology: Twenty-seven adolescent idiopathic scoliotic girls with mild to moderate Cobb angles (10° to 50°) participated in this study. All subjects had at least one set of bi-planar radiographs taken with the EOS® X-ray imaging system prior to any treatment. Subjects were divided into two groups, separating the mild (under 20°) from the moderate (20° and over) spinal scoliotic deformities. Wedging was calculated in three different geometric planes with respect to the smallest edge of the vertebral body.

Results: Factorial analyses of variance revealed a main effect for the scoliosis severity but no main effect of vertebral Levels (apex and each of the three vertebrae above and below it) (F = 1.78, p = 0.101). Main effects of vertebral Positions (apex and above or below it) (F = 4.20, p = 0.015) and wedging Planes (F = 34.36, p<0.001) were also noted. Post-hoc analysis demonstrated a greater wedging in the inferior group of vertebrae (3.6°) than the superior group (2.9°, p = 0.019) and a significantly greater wedging (p≤0.03) along the sagittal plane (4.3°).

Conclusions: Vertebral wedging was present in mild scoliosis and increased as the scoliosis progressed. The greater wedging of the inferior group of vertebrae could be important in estimating the most distal vertebral segment to be restrained by bracing or to be fused in surgery. Largest vertebral body wedging values obtained in the sagittal plane support the claim that scoliosis could be initiated through a hypokyphosis.

Figure 1. Selected landmarks and measured angles on each thoracic and lumbar vertebrae.

Points represent the eight vertebral body corners as seen on the radiographs. The spatial angles were measured with respect to the smallest edge (SE) representing the frontal, sagittal and diagonal planes wedging. Ψ, φ and θ represent respectively the postero-frontal, sagittal and diagonal angles with 1 and 2 indicating the superior and inferior angles. Each superior and inferior angles of a plane were summated to characterize vertebral wedging.

Figure 2. Thoracic and lumbar vertebrae digitization.

Firstly a bony landmark was identified on the postero-anterior radiograph. A horizontal line drawn from this point was projected on the lateral radiograph. The intersection between the horizontal line and the edge of the vertebral body ensured that the same bony landmark was identified in each pair of radiographs.

Figure 3. Extent of wedging at the apex and at each of three vertebrae above and below.

Circles represent the average wedging and bars represent the 95% confidence interval. The mild scoliosis group is in blue and the moderate scoliosis group is in green.

Figure 4. Combined effect of three superior and three inferior vertebrae wedging compared to the apex vertebra.

Circles represent the average wedging and bars represent the 95% confidence interval. The mild scoliosis group is in blue and the moderate scoliosis group is in green.

Figure 5. Vertebral wedging values obtained for the frontal, sagittal and diagonal edges.

Circles represent the average wedging and bars represent the 95% confidence interval. The mild scoliosis group is in blue and the moderate scoliosis group is in green.