As with all spinal fusion surgery, a posterior lumbar interbody fusion (PLIF) 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 cage made of either allograft bone or synthetic material (PEEK or titanium) 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 cage made of allograft bone, or posterior lumbar interbody cages with bone graft, is then inserted into the disc space and the bone grows from vertebral body to vertebral body.
PLIF Potential Advantages and Disadvantages
Doing a pure PLIF 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 (an ALIF, 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 larger spinal implant can be inserted from an anterior approach, which provides for superior stabilization.
- 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 cage posteriorly will allow it to retro pulse back into the canal and create neural compression.
PLIF surgery has a higher potential for a solid fusion rates 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.
PLIF Potential Risks and Complications
The principal risk of a PLIF is that a solid fusion will not be obtained (nonunion), and further back surgery to re-fuse the spine may be necessary. Fusion rates for a PLIF should be as high as 90-95%.
Nonunion rates are higher for patients who have had prior spine surgery, patients who smoke or are obese, patients who have had a multiple level fusion surgery, and for patients who have been treated with radiation for cancer. Not all patients who have a nonunion will need to have another spine fusion procedure. As long as the joint is stable, and the patient's symptoms are better, more back surgery is not necessary.
Other than nonunion, the risks of a spinal fusion surgery include infection or bleeding. These complications are fairly uncommon (approximately 1% to 3% occurrence). In addition, there is a risk of achieving a successful spine fusion, but the patient's pain does not subside.