A surgical procedure performed to eliminate spinal pain or immobilize unstable joint segments. Can be used to treat degenerative disc disease and to immobilize injured vertebral segments. A bone graft is placed across a spinal segment which then grows together with the patient’s bone and the area is immobilized. There is a loss of motion between two vertebrae that are fused together. The graft can be an autograft (bone taken from the patient) or an allograft (cadaver bone).