The SRS–Lenke–Aubin 3D classification of adolescent idiopathic scoliosis

PURPOSE: Adolescent idiopathic scoliosis (AIS) is a complex three-dimensional (3D) spinal deformity, with transverse plane rotational components increasingly targeted by modern surgical techniques. Yet, clinical evaluation remains predominantly based on 2D radiographic parameters, including the widely used Lenke classification. In response, the 3D Classification Task Force of the Scoliosis Research Society (SRS) developed a comprehensive, clinically relevant classification system that remains intuitive, reproducible, and readily applicable by spine surgeons. This manuscript introduces the proposed SRS-Lenke-Aubin 3D classification and evaluates its ability to provide a structured and clinically meaningful 3D characterization of spinal deformities in AIS. METHODS: To maintain continuity with standard clinical practices, the system builds upon the established Lenke classification and introduces two complementary 3D descriptors: the orientation of the regional plane of deformation (ORPD) and the apical vertebral rotation (AVR). These indices capture transverse plane deformities at the regional and local levels, respectively. Each was independently assessed for the proximal thoracic (PT), main thoracic (MT), and thoracolumbar/lumbar (TL/L) regions using calibrated 3D reconstructions from biplanar radiographs. A population-representative cohort of 285 AIS surgical cases was used to evaluate the system. ORPD and AVR values were translated into categorical modifiers using predefined clinical thresholds. RESULTS: The new SRS-Lenke-Aubin 3D AIS classification adds two transverse plane modifiers per spinal region-the ORPD and AVR-yielding a modular 3-tiered, 4-modifier system: Curve type (1-6), Lumbar spine modifier (A, B, C), Thoracic sagittal profile modifier (-, N, +), Transverse plane regional modifier (ORPD: 1-3) and Transverse plane local modifier (AVR: s, m, l). A broad range of ORPD × AVR combinations was observed across the cohort, reflecting the system's ability to capture transverse plane heterogeneity. Notably, similar coronal curve types often exhibited divergent transverse morphologies, underscoring the added value of these 3D descriptors in identifying clinically relevant variation. CONCLUSIONS: The SRS-Lenke-Aubin 3D classification enriches the existing Lenke framework by incorporating practical transverse plane descriptors compatible with standard imaging workflows. This system offers a clinically meaningful step toward more complete 3D characterization of AIS, with potential applications in improving surgical planning, assessing outcomes, and supporting future integration with automated 3D tools.