Assessing progressive changes in axial plane vertebral deformity in adolescent idiopathic scoliosis using sequential magnetic resonance imaging.

Abstract

To understand how the axial plane deformity contributes to progression of the three-dimensional spinal deformity of Adolescent Idiopathic Scoliosis (AIS), with a main thoracic curve type, using a series of sequential magnetic resonance images (MRI). Twenty-seven AIS patients (at scan 1: mean 12.4 years (± 1.5), mean Cobb angle 29.1°(± 8.8°)) had 3 MRI scans (T4-L1) performed at intervals of mean 0.7 years (± 0.4). The outer profile of the superior and inferior endplates were traced on a reformatted axial image using ImageJ (NIH). Endplate AVR, and intravertebral rotation (IVR), defined as the difference between superior and inferior endplate AVR, was calculated for each vertebral level. For all patients and scans, the mean AVR was greatest at the curve apex, with AVR diminishing in a caudal and cephalic direction from the apex. At scan 3 the mean apical AVR was 15.1°(± 4.6°) with a mean change in apical AVR between MRI 1 and 3 of 2.7°(± 2.9°). The increase in standing height between MRI 1 and 3 was mean 7.4 cm (± 4.6). Linear regression showed a positive correlation between apical AVR and Cobb angle (R² = 0.57, P < 0.001), and a positive correlation between apical AVR and rib hump (R² = 0.54, p < 0.001). The mean change in IVR was greater 3 vertebral levels cephalic and caudal to the apex (1.4°(± 4.1°) and 1.2°(± 2.0°), respectively), compared to the apex (0.4°(± 3.1°)). AVR increased, during curve progression, most markedly at the curve apex. The greatest IVR was observed at the periapical levels, with the apex by contrast having only a modest degree of rotation, suggesting the periapical vertebral levels of the scoliosis deformity may be a significant driver in the progression of AIS.