Comment faut-il cintrer les tiges pour restaurer l'alignement sagittal tout en garantissant une correction 3D efficace de la scoliose idiopathique adolescente ? Une étude biomécanique personnalisée au patient

Aims:In adolescent idiopathic scoliosis (AIS) surgery, rod contouring influences 3D correction and sagittal alignment. Rod flattening during insertion may alter the intended sagittal profile, prompting surgeons to empirically overcontour rods, typically by approximately 20°. However, flattening varies with spinal stiffness, preoperative curvature, and initial rod contour. This study evaluated five rod-contouring strategies considering preoperative thoracic kyphosis (TK), a patient-specific TK target derived from pelvic incidence (PI), and rod flattening measured and reported in published biomechanical studies. Material and methods:Patient-specific physics-based spine models were created for 32 thoracic AIS patients. Five rod-contouring strategies were tested: a calculated contour incorporating preoperative TK, patient-specific target TK [TK = 2(PT + LL - PI)], and reported rod flattening (22°/48%); two variants accounting for ±15% variation in flattening; 20° overcontouring; and a standardized contour identical across patients. Primary correction maneuvers were simulated using 5.5-mm cobalt-chromium (CoCr) rods and bilateral uniaxial screws. Correction was assessed in the coronal, sagittal, and axial planes. Results:The standardized contour produced significantly worse coronal (MT Cobb: 27±5°) and sagittal correction (deviation from target TK: 13±10°) than the other strategies (24±5° and 9±7° respectively, p<0.05), with similar axial correction (AVR: 15±7° vs 17±7°). MT Cobb, TK target deviation and AVR values for the other strategies were similar, including: calculated contour (25±5°/9±6°/16±7), the two ±15% variants in flattening (25±5°/9±6°/17±8°, and 24±5°/9±7°/17±7°) and the 20° overcontouring (24±5°/10±7°/17±7°). Conclusion:A standardized rod contour appears suboptimal for coronal and sagittal correction. Accounting for preoperative sagittal alignment, a patient-specific TK target, and rod flattening may better guide rod contour while maintaining 3D correction. Significance:These findings are a first step toward biomechanically informed, patient-specific rod-contouring strategies and future optimization integrating patient, deformity, and construct characteristics.