In the spinal fusion surgery what we do is we put screws in the pedicles. Pedicles are the bones which concept the posterior or back elements with the front body. So through that we put screws, suppose ne level, two level. If it is one level we have to put 4 screws, 2 above and 2 below. On each side one screw each. After putting the screws we have to decompress the spine, after w e decompress the spine we remove al the disc and in that space we put bone grafts and we put a cage, cage is like a brick. It is a metal brick. So we have to put bone graft in the metal brick and keep it inside the intervertebral disc. So that means the disc height is maintained. So after that we put rod is either part of the spine and put nuts and tighten it. So that means that segment becomes stable. So two bones still behave as one bone. So this is usually necessary for a patient with chronic back pain which is having instability of the spine.
