Posterior Lumbar (surgery from the back) fusion surgery is performed to promote the growth of separate bones into one solid unit of bone. Typically rods, held in place by screws are used in the procedure to act as a permanent cast. The procedure may involve the removal of the disc and some of the bone to make more room for the nerves, with the possible placement of an interbody (cage) fusion device. Fusion does not occur immediately with surgery, but happens over time as your body builds bone at the surgery site. Typically, this is the procedure of choice if there is significant degenerative disease (arthritis) at several levels. Because the goal of the procedure is to fuse the bones together, motion of the back may be limited in both up and down and side to side movements.