Posterolateral gutter fusion surgery is the gold standard surgical approach to achieve spinal fusion. This surgical approach involves placing bone graft in the posterolateral portion of the spine (area just outside the spine). An incision is made at the midline of the back and bone graft is placed underneath the large back muscles that attach to the transverse processes of the affected vertebrae. The posterolateral vascular area is important to the fusion since it carries blood and nutrients to the site of fusion. The principal risk of this type of low back surgery is if a solid fusion is not obtained (nonunion) and further surgery to re-fuse the spine may be necessary.