Imaging findings following spinal fusion surgery in which rhBMP is used include heterotopic bone formation, bone resorption/osteolysis, cage migration, and soft tissue inflammation. A history of spinal surgery in which rhBMP has been utilized and comparison with preoperative imaging studies are most helpful in assessing the presence of these findings and determining if findings warrant further investigation or are part of the expected postoperative course. The differential diagnosis for rhBMP-induced osteolysis includes Schmorl’s node, interbody spacer subsidence, fracture, postoperative discitis/osteomyelitis, and lytic tumor (Fig. 52.2). On the other hand, the differential diagnosis for heterotopic bone formation with rhBMP includes graft migration or extrusion, adjacent level degenerative changes, calcified disc herniation, myositis ossificans, and osteoblastic tumor (Fig. 52.3).