Transforaminal Lumbar Interbody Fusion or TLIF (pronounced T-lif) is a type of spinal fusion surgery designed to permanently fuse, or unite, bones of the lower spine. TLIF involves approaching the spine from the back, completely removing a disc between two vertebrae, placing a bone graft where the disc used to be, and locking the two vertebrae using hardware. TLIF is considered only after non-surgical treatments have failed.