Fusing vertebrae in the lumbar spine may help ease lower back and leg pain. Spinal fusion is fusing two or more vertebrae together so they heal into a single, solid bone. The goal of spinal fusion is to reduce or eliminate painful motion and restore the stability of the spine. Posterior lumbar fusion is done through an incision in your back. Spacers, a bone graft, or both are put between the vertebrae. Depending on how many vertebrae are fused, the surgery may take from 3 to 8 hours.