As with all spinal fusion surgeries, the PLIF and TLIF procedures involve adding bone graft or bone graft substitute 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.

The success rate for posterior fusion in the treatment of refractory discogenic back pain is only 60-70%. The selection of the appropriate patient for this surgery has been blamed for the relatively poor results. Other possible causes of poor results are that the actual pain-causer, the disc, is not addressed. Studies have shown continued significant movement of the disc despite solid posterior fusion. One study showed that patients with continued back pain after solid posterior fusion were improved after anterior fusion of the disc space.

This image shows a side view of an instrumented spine. The arrow shows the force of gravity which is diverted from the disc to the posterior instrumentation. One can imagine how the disc space could continue to have motion despite solid posterior fusion.

In an attempt to improve the results of fusion surgery, fusion of the disc has been performed to directly address the most common source of pain. Unlike the posterolateral gutter fusion, the PLIF achieves spinal fusion by inserting bone graft and possibly instrumentation directly into the disc space. The disc excision and fusion can be performed anteriorly, or through a posterior approach. When the posterior approach is used to remove and fuse the disc, this is called a PLIF, Posterior Lumbar Interbody Fusion.

An alternative approach is used to minimize retraction of the dura. By resecting the facet joint, a farther lateral approach can be used to remove the disc. This approach, with removal of the facet, is called a TLIF - Transforaminal Lumbar Interbody Fusion.

General Procedure

1. 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 back muscles (erector spinae) are stripped off the lamina on both sides and at multiple levels.
   
   
2. After the spine is approached, to perform the PLIF procedure (shown below), the lamina is removed (laminectomy) which allows visualization of the nerve roots. The facet joints, which are directly over the nerve roots, are usually undercut to give the nerve roots more room and more room for performing the fusion and/or instrumentation. For the TLIF procedure (shwon below), the entire facet joint is removed.
   
   
3. The nerve roots are then retracted to one side and the disc space is cleaned of the disc material. Bone graft is then inserted into the disc space with or without interbody cages. For a standard PLIF procedure, the bone graft and/or instrumentation is performed on both sides. For the TLIF procedure, the disc space is accessed from one side, reaching over to remove and replace the disc on the other side.

The TLIF approach is shown below, with removal of the disc. Bone graft, bone from the bone bank, or instrumentation in the form of a cage can be placed through this approach.