A Narrative Review of Implant Density and Surgical Outcomes in Adolescent Idiopathic Scoliosis

Abstract

Pedicle screw instrumentation is the standard of care for posterior spinal fusion in adolescent idiopathic scoliosis (AIS) because of its superior biomechanical stability and ability to facilitate 3D deformity correction, but despite widespread adoption, the optimal pedicle screw density required to achieve durable correction while minimizing complications and cost remains controversial. The purpose of this study is to synthesize available evidence evaluating the relationship between pedicle screw density and radiographic, functional, perioperative, and economic outcomes in AIS surgery. A narrative review of the literature was conducted using PubMed and Google Scholar, including English-language studies examining the association between implant density and surgical outcomes in AIS and young adult idiopathic scoliosis. Thirty studies were ultimately included, with the majority demonstrating no consistent association between higher implant density (ID) and improved radiographic correction or functional outcomes, as low-density constructs achieved comparable coronal and sagittal correction, health-related quality-of-life scores, and maintenance of correction. Conversely, higher ID was consistently associated with increased operative time, blood loss, and implant-related cost, and while select studies suggested improved correction with higher-density fixation in specific curve types or patterns, these effects diminished when curve flexibility and surgical strategy were considered. Ultimately, current evidence suggests that higher pedicle screw density does not reliably confer superior radiographic or functional outcomes in AIS, while conversely increasing operative demand and cost, meaning that low-density constructs represent a safe and effective alternative in appropriately selected patients.