Radiographic predictors of lateral translation in patients with residual adolescent idiopathic scoliosis and thoracolumbar/lumbar curves: A focus on L3 lateral translation.

Background: Patients with residual adolescent idiopathic scoliosis (AIS) and thoracolumbar/lumbar (TL/L) curves may present with progression after cessation of growth, with lateral translation as a major risk factor. Nonetheless, radiographic predictors and underlying mechanisms remain indefinite. This study aimed to determine these radiographic predictors and structural mechanisms in patients with residual AIS.

Methods: Radiographic and clinical data were collected from 45 consecutive patients with preoperative residual AIS and TL/L Cobb angle >40° who subsequently underwent corrective surgery at our institution. Lateral translation was defined as intervertebral slippage ≥6 mm on computed tomography. Statistical analyses included Student's t-test, Pearson's correlation coefficients, receiver operating characteristic (ROC) curve analysis, and multivariate logistic regression analysis.

Results: Out of 45 patients, 3 were male, whereas 42 were female, with a mean age of 40.6±17.4 years. L3 slippage was observed in 21 patients, resulting in the categorization into the slippage and non-slippage cohorts. Multivariate logistic regression analysis revealed statistically significant disparities in the bilateral facet angles, facet joint opening, and facet joint vacuum phenomenon between the two cohorts. The ROC analysis determined a 20.5° cut-off value for predicting L3 slippage. In the non-slippage cohort, a strong correlation was particularly observed between L3 slippage and L2-L3 bridging.

Conclusion: Facet joint instability, L4 tilt ≥20.5°, and L3 cranial vertebral bridging are predictive radiographic factors for L3 lateral translation in patients with residual AIS. Thus, patients exhibiting these characteristics require consistent follow-up or early surgical intervention before lateral translation occurs.