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

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.