Contribution of coronal vertebral and IVD wedging to Cobb angle changes in adolescent idiopathic scoliosis during growth

Abstract

Study design: Prospective study BACKGROUND: Vertebral and intervertebral disc (IVD) wedging are often seen in patients with adolescent idiopathic scoliosis (AIS). However, the relationship between wedging and curve progression, and the change of wedging before bracing to final weaning is unknown. The aim of this study was to investigate the pattern and sequence of vertebral and IVD wedging development, and to determine the relationship between the change of wedging and curve progression in AIS during growth.

Methods: This was a prospective study of 32 AIS females with right-sided thoracic curves and/or left-sided lumbar curves who completed brace treatment. They were classified into progression and non-progression groups. Vertebral and IVD wedging were calculated for each spinal segment. The wedging pattern was first identified and then used to determine the sequence of wedging development. Percentage change in the sum of wedging during growth was calculated and compared.

Results: The sum of vertebral wedging for both groups was 2.4° to 8.7° more than that of IVD wedging in the thoracic spine but 8.7° to 17.7° less in the lumbar spine. Out of the 20 curves assessed, 5 thoracic curves and 1 lumbar curve developed vertebral wedging before IVD wedging, and 3 thoracic curves and 4 lumbar curves had the opposite pattern. The progression group had larger increases in sum of vertebral (40%) and IVD (28.6%) wedging as compared to the non-progression group (both 16.7%). A significant difference in wedging between the first and the latest visits was found in the progression group only (p < 0.05).

Conclusion: Pattern and sequence of vertebral and IVD wedging were related to the location of the curve rather than the presence of curve progression. Progressed curves were associated with increased wedging during growth.

Level of evidence: II.

Keywords: Adolescent idiopathic scoliosis; Deformity; Disc; Wedging.

Fig. 1

Steps in the measurement process. a Original X-ray. b After the X-ray was imported into MATLAB, a filter was used to enhance image contrast. c Lines across the superior and inferior endplates of each vertebra were drawn. d The lines passing through the superior and inferior endplate of the vertebra (red line) were used to calculate vertebral wedging while lines passing through the inferior endplate of the cranial vertebra and superior endplate of the caudal vertebra (green line) were used to calculate IVD wedging. e Vertebral and f IVD wedging were presented in a line graph to observe the change of wedging along the spine

Fig. 2

Pattern detection. If the wedging was maximum at the apex and decreased to the upper and lower vertebrae, this indicated the presence of a wedging pattern

Fig. 3

Curve classification. If the maximum sum of wedging was found at the first clinical visit, the percentage decrease from the first visit to the latest visit was calculated. If the maximum sum of wedging was found at the latest visit, the percentage increase from the first visit to the latest visit was calculated. If the maximum sum of wedging was found after the first visit and before the latest visit, the percentage increase from the first visit to the maximum sum and the percentage decrease from the maximum sum to the latest were calculated

Fig. 4

Recruitment flowchart

Fig. 5

Relatively more vertebral wedging in the thoracic curve and more IVD wedging in the lumbar curve. a In the thoracic curve (T1-T6), a pattern of wedging was observed in the vertebral wedging for all visits but not in IVD wedging. The average sum of vertebral wedging was 14.1° while that of IVD wedging was 6.0°. b In the lumbar curve (T12-L4), a pattern of wedging was observed in IVD wedging for all visits but not in vertebral wedging. The average sum of vertebral wedging was 9.2° while that of IVD wedging was 16.4°

Fig. 6

When vertebral wedging developed before IVD wedging. a The wedging pattern was presented at the first clinical visit. b At the first clinical visit, IVD wedging at the apex did not differ from others. It increased with time and was maximum at the fourth visit. Thus, vertebral wedging developed before IVD wedging

Fig. 7

When IVD wedging developed before vertebral wedging. a Vertebral wedging at the apex did not differ from other vertebrae at the first clinical visit. It increased with time and was maximum at the third visit. b The wedging pattern already developed at the first clinical visit. Thus, IVD wedging developed before vertebral wedging

Fig. 8

Curves were excluded from the Progression group when assessing the relationship between change in wedging and curve progression. 6 minor curves were excluded as the Cobb angle was increased less than 10°

Fig. 9

Progressed curves. a X-ray at the first clinical visit. T7/L1 = 24.3°. L1/L4 = 16.7°. b X-ray of the latest clinical visit. T7/L1 = 60°. L1/L5 = 37.6°. c Vertebral wedging of the thoracic curve. At the early stage of scoliosis, the wedging increased from T9 to T10 and then decreased to T11. The wedging increased from T8 to T10 and then decreased to T12. The wedging at the apex (T10) increased from 4.4° at the first clinical visit to 17.0° at the latest visit. d IVD wedging of the lumbar curve. The wedging at the apex (L2/L3) increased gradually from 5.4° at the first clinical visit to 10.0° at the latest visit. e Summation of the wedging value of the thoracic curve. Given that a gradual increase in wedging was found in vertebral wedging, the sum of the vertebral wedging was from 13.1° to 44.4°. f Summation of the wedging value of the lumbar curve. Given that a gradual increase in wedging was found in IVD wedging, the sum of the IVD wedging was from 17.3° to 28.4°

Fig. 10

Non-progressed curves. a X-ray at the first clinical visit. T4/T11 = 25.2°. T11/L4 = 45.7°. b X-ray of the latest clinical visit. T4/T11 = 26°. T11/L4 = 35°. c Vertebral wedging of the curve T11/L4. The wedging at the apex (L2) increased by 0.5° at the 3rd clinical visit. d IVD wedging of the curve T11/L4. The wedging at the apex (L1/L2) was maintained at around 10°. e Summation of the wedging value of the lumbar curve. The sum of vertebral wedging decreased from 13.9° to 12.9° and that of IVD wedging decreased from 35.8° to 28.8°