Predictive factors for greater than 15° thoracic kyphosis gain following surgery for adolescent idiopathic scoliosis: a retrospective comparative study in Japan.

Abstract

Retrospective cohort study. To identify factors predictive of a postoperative gain in thoracic kyphosis (TK) of at least 15° after deformity correction surgery for adolescent idiopathic scoliosis (AIS). Conventional treatment strategies for AIS have historically emphasized the correction of coronal deformity despite the higher prevalence of sagittal imbalance in AIS compared to those without spinal deformity. However, recent research has brought attention to the importance of sagittal alignment as a significant determinant of quality of life. We retrospectively reviewed 54 patients (aged ≤20 years) who underwent deformity correction surgery for AIS between 2018 and 2024. Patients were stratified into two cohorts based on the degree of postoperative TK gain: ≥15° or <15°. Both patient groups were comparable in terms of demographic characteristics, including age, sex distribution, height; body mass index, Risser's grade, or follow-up duration (p >0.05). However, those with ≥15° TK gain demonstrated significantly lower preoperative TK (17.7°±9.8° vs. 23.6°±9.9°), greater postoperative change in TK (21.2°±5.4° vs. 6.9°±4.9°, p <0.000), lower preoperative pelvic tilt (10.0°±8.4° vs. 15.6°±7.7°, p =0.014), and significantly higher screw density (74.5%±6.2% vs. 70.3%±5.2%, p =0.006). Other radiological (Cobb angle, apex level, main thoracic curve flexibility, main thoracic curve correction, sagittal vertical axis, lumbar lordosis, and pelvic incidence) and surgical parameters (fusion levels, blood loss, and surgical time) were comparable between groups. Our findings suggest that higher screw density and preoperative sagittal morphology (hypokyphotic thoracic alignment and lower pelvic tilt) influence the degree of TK correction attainable after AIS surgery.