Special screws called "pedicle screws" are placed through the pedicle bone on the back of the spinal column. The screw inserts
through the pedicle and into the vertebral body, one on each side. The
screws grab into the bone of the vertebral body, giving them a good
solid hold on the vertebra. Once the screws are placed they are attached
to metal rods that connect all the screws together. When everything is
bolted together and tightened, this creates a stiff metal frame that
holds the vertebrae still so that healing can occur. The bone graft is then placed around the back of the vertebrae.