S1 Dual Outer Diameter Screws Accelerate Early Fusion Compared with Conventional Pedicle Screws in Posterior Lumbosacral Interbody Fusion

Introduction: Achieving successful lumbosacral interbody fusion is challenging due to the unique anatomical characteristics of the sacrum. The predominantly cancellous bone and short pedicles limit screw purchase, which frequently leads to S1 screw loosening and pseudarthrosis, resulting in persistent pain and poor outcomes. Therefore, the S1 Dual Outer Diameter (DOD) screw, featuring a dual-zone thread design with greater thread depth and sharper edges proximally and reduced thread depth with blunter edges distally, was developed to maximize screw purchase in cancellous and cortical bones. This study aimed to compare the clinical and radiological outcomes of DOD and conventional pedicle screws in posterior lumbosacral interbody fusion.