Sequential Magnetic Resonance Imaging Reveals Individual Level Deformities of Vertebrae and Discs in the Growing Scoliotic Spine.

STUDY DESIGN: The aim of this study was to measure contributions of individual vertebra and disc wedging to coronal Cobb angle in the growing scoliotic spine using sequential magnetic resonance imaging (MRI). Clinically, the Cobb angle measures the overall curve in the coronal plane but does not measure individual vertebra and disc wedging. It was hypothesized that patients whose deformity progresses will have different patterns of coronal wedging in vertebrae and discs to those of patients whose deformities remain stable.

METHODS: A group of adolescent idiopathic scoliosis (AIS) patients each received two to four MRI scans (spaced 3-12 months apart). The coronal plane wedge angles of each vertebra and disc in the major curve were measured for each scan, and the proportions and patterns of wedging in vertebrae and discs were analyzed for subgroups of patients whose spinal deformity did and did not progress during the study period.

RESULTS: Sixteen patients were included in the study; the mean patient age was 12.9 years (standard deviation 1.7 years). All patients were classified as right-sided major thoracic Lenke Type 1 curves (9 type 1A, 4 type 1B, and 3 type 1C). Cobb angle progression of ≥5° between scans was seen in 56% of patients. Although there were measurable changes in the wedging of individual vertebrae and discs in all patients, there was no consistent pattern of deformity progression between patients who progressed and those who did not. The patterns of progression found in this study did not support the hypothesis of wedging commencing in the discs and then transferring to the vertebrae.

CONCLUSION: Sequential MRI data showed complex patterns of deformity progression. Changes to the wedging of individual vertebrae and discs may occur in patients who have no increase in Cobb angle; therefore, the Cobb method alone may be insufficient to capture the complex mechanisms of deformity progression.