MRI in early stages of adolescent idiopathic scoliosis indicates a neuro-osseous growth mismatch associated with curve progression.

Abstract

Purpose: To investigate the relationship between spinal cord anatomy and the risk of curve progression in mild to moderate adolescent idiopathic scoliosis (AIS).

Methods: We prospectively included patients presenting with mild or moderate AIS (< 40 degrees). Irrespective of curve severity, patients underwent 3-dimensional MRI and were followed until skeletal maturity or surgery. Retrospectively, we measured the true lateral cord space (LCS) ratio on transverse cuts of the curve apex. This is a measure of the lateral displacement of the medulla in the spinal canal. The primary outcome measure was curve progression defined as a Cobb angle increase ≥ 10 degrees at follow-up.

Results: Of the 64 included patients, 18 (28%) progressed more than 10 degrees during follow-up. At baseline, mean age in the progression and non-progression group was 13.1 ± 1.6 vs. 15.8 ± 1.5 years (p < 0.001), and mean Cobb angle was 32 ± 7 vs. 26 ± 9 degrees (p < 0.001). The time from baseline x-ray to MRI was 1.3 ± 3 months vs. 1.7 ± 3.6 months (p = 0.738). LCS ratio was 1.5 (IQR: 1.1-1.7) in the progression group and 1.0 (IQR:0.8-1.3) in the non-progression group (p < 0.001). When matched according to baseline Cobb angle and age, median LCS ratio was 1.5 [1.1, 1.7] and 0.9 [0.7-1.2] in the progression and non-progression group, respectively (p < 0.001).

Conclusions: We found significant displacement of the medulla towards the concavity of the curve in progressive AIS. This finding supports the theory of a neuro-osseous growth mismatch as a part of the etiopathophysiology of AIS and may play a predictive role in prognosis of milder cases of AIS.