In fusion surgery (also called arthrodesis) two bones are fused together to form a single piece of bone tissue. When fusion surgery is done with vertebrae in the spine, the bones are fused together and the disc space between them no longer exists. Thus, two vertebrae are fused together to form a single, solid bone.
A bone grafting material is used to stimulate the fusion process. The bone graft will be placed in the space between the two vertebrae (i.e., intervertebral disc space). There are a range of bone grafting materials that a surgeon can use.