Demands on Posterior Fusion Hardware During Lordosis Restoration Procedures

Lower lumbar lordosis plays a critical role in sagittal alignment. It has been shown that restoration of lumbar lordosis in patients with preoperative sagittal imbalance is necessary to prevent postoperative sagittal decompensation [1]. Further, restoration of lower lumbar lordosis in patients with degenerative flatback syndrome has been shown clinically to result in additional correction of the thoracic curve and sacral slope [2]. Currently, there are three commonly used intraoperative techniques to restore lumbar lordosis: (1) cantilever bending, (2) in situ bending, and (3) compression and/or distraction of screws along posterior fusion rods. Although powerful, all three techniques require the surgeon to impart large forces to the accompanying posterior fusion hardware, often causing failure of hardware and inconsistency to achieve pre-operatively planned lordosis. To date, there has been no clinical or biomechanical study to address the comparative performance of these three techniques. In efforts to determine a standard of care for sagittal alignment via lumbar lordosis restoration, the goal of this study is to establish a relation between the three techniques, and the resulting demands on posterior fusion hardware. It is hypothesized that greater loads will be observed in the hardware during in situ bending, increasing the risk of pedicle screw pullout.