Radiographic characterization and predictive modeling of functional scoliosis secondary to leg length discrepancy in adolescents.

BACKGROUND

Leg length discrepancy (LLD) frequently induces reversible functional scoliosis, but clinically distinguishing it from progressive structural scoliosis remains challenging. Moreover, clear imaging diagnostic criteria for functional scoliosis have not yet been established. This study aims to characterize functional scoliosis caused by LLD, differentiate it from structural scoliosis concomitant with LLD, and develop a diagnostic model to guide clinical decision-making.

METHODS

A retrospective study of 236 patients with LLD was conducted. Full-spine and lower-limb radiographs were analyzed. Radiological parameters [LLD, structural LLD (SLLD), pelvic obliquity angle (POA), femoral head height difference (FHHD), lumbar Cobb angle, sacral obliquity angle (SOA), coronal balance distance (CBD)] and clinical outcomes post-limb elevation were measured. Statistical comparisons and correlation analyses were performed. And a least absolute shrinkage and selection operator (LASSO)-based prediction model was developed using lumbar Cobb, FHHD, SOA, femoral length inequality (FLI), and CBD.

RESULTS

Functional scoliosis showed ipsilateral pelvic tilt and contralateral lumbar curvature, with L3 as the most frequent apical vertebra. Functional scoliosis exhibited lower SLLD (P<0.001), lumbar Cobb (P<0.001), and CBD (P=0.003). LLD and SLLD correlated with POA and lumbar Cobb (P<0.001) but not CBD. The prediction model achieved areas under the curve (AUCs) of 0.938 (training set) and 0.866 (test set), with key predictors including lumbar Cobb, FHHD, and CBD.

CONCLUSIONS

Functional scoliosis due to LLD predominantly involves the lumbar spine, correlates with pelvic tilt, and improves with limb elevation. Structural scoliosis is associated with greater Cobb angles and coronal imbalance. The diagnostic model reduces reliance on repeated radiographs, aiding targeted management. Lumbar Cobb angle, FHHD, and CBD are critical discriminators, enhancing clinical decision-making for surgical or non-surgical interventions.