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 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 thoracolumbar/lumbar 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 curve analysis, and multivariate logistic regression analysis.

Results: 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 nonslippage cohorts. Multivariate logistic regression analysis revealed statistically significant disparities in the bilateral facet angles, facet joint opening, and facet joint vacuum phenomenon between the 2 cohorts. The receiver operating characteristic analysis determined a 20.5° cut-off value for predicting L3 slippage. In the nonslippage cohort, a strong correlation was particularly observed between L3 slippage and L2-L3 bridging.

Conclusions: 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.