Quantification of chest deformity correction in anterior and posterior spinal fusion for adolescent idiopathic scoliosis

Introduction: Chest deformation is the main factor influencing cosmesis and pulmonary function in patients with severe thoracic adolescent idiopathic scoliosis (AIS). This study examined changes in thoracic and spinal deformity in patients with primary thoracic AIS undergoing anterior (ASF) and posterior spinal fusion (PSF). Methods: Pre- and postoperative radiographs and low-dose CT-scans of 54 AIS patients who underwent either ASF (n = 24) or PSF (n = 30) for primary thoracic curves were collected. Chest deformity parameters were measured at the apex and included hemithoracic-width ratio (HWr), rib-hump index (RHi), thoracic rotation (TR), endo-thoracic hump ratio (EHr) and spinal penetration index (SPi). Results: In the PSF group, HWr (0.6 to 0.7, p < 0.001) and TR (25° to 19°, p < 0.001) improved while RHi (p = 0.714) and EHr (p = 0.665) remained unchanged. SPi (12.1% to 12.9%, p = 0.004) worsened. In the ASF group, HWr (0.5 to 0.7, p < 0.001), TR (32° to 20°, p < 0.001) and RHi (28% to 20%, p = 0.020) improved while EHr (p = 0.108) and SPi (p = 0.754) remained unchanged. On average, neither technique decreased the spinal penetration into the chest. Moderate correlation was observed between increased postoperative thoracic kyphosis and decreased SPi. Conclusion: While ASF and PSF both correct the coronal and axial chest deformation in AIS, and an increase in kyphosis correlates to a reduction of spinal intrusion. Neither approach alters the sagittal intrusion of the spine into the chest directly postoperatively. However, comparisons should be interpreted as descriptive given baseline differences.