Comparative effectiveness of different pedicle screw density patterns in spinal deformity correction of small and flexible operative adolescent idiopathic scoliosis: inverse probability of treatment weighting analysis

Abstract

Purposes: An optimal pedicle screw density for spinal deformity correction in adolescent idiopathic scoliosis (AIS) remains poorly defined. We compared radiographic correction, operative time, estimated blood loss, and implant cost among different screw density patterns in operatively treated AIS patients. Methods: A retrospective observational cohort study of AIS patients who underwent posterior spinal fusion using all-pedicle screw instrumentation was conducted from January 2012 to December 2018. All patients were categorized into three different pedicle screw density groups: the very low density (VLD), the low density (LD), and the high density (HD) group. The comparative effectiveness between each pairwise comparison was performed under the inverse probability of the treatment weighting method to minimize the possible confounders imbalance among treatment groups. The primary endpoints in this study were the degrees of correction and deformity progression at 2 years postoperatively. Results: A total of 174 AIS patients were included in this study. The adjusted treatment effects demonstrated similar degrees of deformity correction after 2 years in the three treatment groups. However, the VLD and LD group slightly increased the curve progression at 2 years compared to the HD group by 3.9° (p = 0.005) and 3.2° (p = 0.044), respectively. Nevertheless, the limited screw density patterns (VLD and LD) significantly reduced the operative time, estimated blood loss, and implant cost per operated level. Conclusion: The limited pedicle screw pattern (VLD and LD) in relatively flexible AIS spinal deformity correction results in similar coronal and sagittal radiological outcomes while reducing operative time, estimated blood loss, and implant cost compared to the high-density pedicle screw instrumentation.