Relationship between the different torsion-related thoracic deformity parameters of adolescent idiopathic scoliosis.

INTRODUCTION: Torsion has recently become essential in curve evaluation, not only to assess the degree of clinical deformity that can influence decision making, but also to predict curve progression. Since torsion cannot be currently measured using plain X-rays, our aim was to study the relationships between the different torsion-related parameters measured on 2D radiographs that can indirectly guide the clinician about the torsion of a given curve.

METHODS: This is a cross-sectional study analyzing prospectively registered data of a consecutive cohort of 113 AIS patients with progressive main thoracic deformity. Demographic data, the Adams test and eight radiographic torsion-related coronal and sagittal deformity parameters [apical vertebral rotation (AVR)-Stokes method, Mehta angle (RVAD), main thoracic Cobb side-bending, T5-T12 kyphosis, T5-T8 kyphosis, T9-T12 kyphosis, kyphotic change and double rib contour sign (rib index)] were correlated between each other and with the main thoracic Cobb angle (MTCobb). Univariate linear regression and multiple linear stepwise regression analyses were performed as well.

RESULTS: The radiographically measurable deformity parameters that best correlated with the MTCobb angle in idiopathic curves were: side-bending, RVAD, AVR and the Adams test. Sagittal variables were correlated the least with MTCobb. Coronal parameters as AVR, RVAD, side-bending and Adam test are highly intercorrelated. Sagittal variables are related between each other but are not directly related to coronal parameters.

CONCLUSIONS: There is a strong relationship between the Cobb angle, curve bending, the Mehta angle and the apical vertebral rotation. Together with the clinical Adams test, these are the most important radiographic torsion-related parameters to measure when assessing scoliosis in 2D.

LEVEL OF EVIDENCE: 3.