Vascularized bone flaps for thoracolumbar and lumbosacral spine fusion were developed in dissections on 52 cadavers, using iliac wing bone based on (1) the quadratus lumborum muscle and (2) the deep circumflex iliac artery. Fifteen clinical fusions were performed using these procedures. It was demonstrated roentgenologically that these vascularized bone flaps do not undergo resorption but maintain bone density 1.5 to 2 times that of nonvascularized bone. Bone flaps with a dual blood supply demonstrated increased strength of bony fusion.