Posterior Lumbar Interbody Fusion (PLIF)

As with all spinal fusion surgery, a posterior lumbar interbody fusion (PLIF) surgery involves adding bone graft to an area of the spine to set up a biological response that causes the bone to grow between the two vertebral elements and thereby stop the motion at that segment. Unlike the posterolateral gutter fusion, the PLIF achieves spinal fusion in the low back by inserting a bone graft and/or spinal implant (e.g. cage) directly into the disc space. When the surgical approach for this type of procedure is from the back it is called a posterior lumbar interbody fusion (PLIF). A PLIF fusion is often supplemented by a simultaneous posterolateral spine fusion surgery.

Posterior lumbar interbody fusion surgery description
First, the spine is approached through a three-inch to six-inch long incision in the midline of the back and the left and right lower back muscles (erector spinae) are stripped off the lamina on both sides and at multiple levels. After the spine is approached, the lamina is removed (laminectomy) which allows visualization of the nerve roots. The facet joints, which are directly over the nerve roots, may then be undercut (trimmed) to give the nerve roots more room. The nerve roots are then retracted to one side and the disc space is cleaned of the disc material. A bone graft, or anterior interbody cages with bone, is then inserted into the disc space and the bone grows from vertebral body to vertebral body. Doing a pure PLIF spine surgery has the advantage that it can provide anterior fusion of the disc space without having a second incision as would be necessary with an anterior/posterior spine fusion surgery. However, it has some disadvantages:

Not as much of the disc space can be removed with a posterior approach (from the back).
An anterior approach (from the front) provides for a much more comprehensive evacuation of the disc space and this leads to increase surface area available for a fusion.
A much larger bone graft and/or spinal implant can be inserted from an anterior approach
In cases of spinal deformity (e.g. isthmic spondylolisthesis) a posterior approach alone is more difficult to reduce the deformity
There is a small but finite risk that inserting a bone graft or cage posteriorly will allow it to retropulse back into the canal and create neural compression

PLIF surgery rates are higher than posterolateral fusion rates because the bone is inserted into the anterior portion (front) of the spine. Bone in the anterior portion fuses better because there is more surface area than in the posterolateral gutter, and also because the bone is under compression. Bone in compression heals better because bone responds to stress (Wolff's law), whereas bone under tension (posterolateral fusions) does not see as much stress.