Bone void fillers for spine fusion The FDA has approved several bone graft substitutes as bone void fillers. This is a broad approval based on a product’s ability to supplement or replace autograft (patient’s own bone) in various orthopedic applications. It is not specifically a “bone graft substitute” approval. Most of the bone void filler products contain a porous type of calcium in various configurations (subh as hydroxyapatite, tricalcium phosphate, or calcium sulfate). These substances create a porous environment (a scaffolding) for bone growth. Bone void fillers do not contain bone morphogenic proteins (BMP), although osteogenic factors may be added using techniques such as platelet-rich autologous growth factors derived from the patient’s own blood. Many bone graft substitutes seem to work well combined with a structural spacer in the anterior intervertebral space for an anterior fusion (in the front of the spine). This makes sense since the intervertebral space is exposed (through endplate preparation) to a variety of the patient’s own bone morphogenic protein and osteoblasts, and a scaffolding for the bone to grow into seems to be all that is needed. Bone void fillers may also be used posteriorly (in the back of the spine) to extend or add bulk to autograft. More research is needed before it is known whether any of these fillers can function as effective bone graft substitutes posteriorly without supplemental autograft.