The major difference between a posterolateral lumbar fusion (PLF) and a PLIF procedure is whether or not an interbody spacer is placed. In a PLF, the nerve roots are decompressed directly in the same way they are during a PLIF. In a PLF, the disc spaces are kept intact, and the vertebra are fused across the transverse processes purely with rods and screws. In a PLIF, the disc is removed and an interbody spacer is placed, allowing for fusion to be obtained both in the disc space and across the transverse processes.