Posterior Lumbar Interbody Fusion (PLIF)

Introduction

The technique of posterior lumbar interbody fusion (PLIF) is an important technique in the current spine surgeon’s armamentarium. That being said, the surgery is still defined by its level of technical difficulty and controversy exists regarding the safety of PLIF compared with other approaches to the intervertebral space.

The first in-depth description of a PLIF was described by Cloward, as an operation where the disk space is exposed from a posterior approach and a fusion is performed by directly grafting the intervertebral space. Classically, PLIF is performed via bilateral MEDIAL facet resection and exposure of the disk space; with retraction of the dura, the disk is visualized. Initially, some advocated that the procedure be maintained at the height of the neural foramen after diskectomy, preventing collapse and keeping the nerve root free of bony compression. The procedure also has the advantage of potentially increasing the fusion rate by direct graft-to-bone contact with compressive force (i.e., by placing the bone graft in the intervertebral space).

Posterior lumbar interbody fusion added extensively to the procedure of lumbar fusion, but it is not without its downsides. The procedure (see below) requires resection of the medial facet and retraction of the dura and traversing nerve root to visualize the disk space in order to perform the interbody fusion. At times, this retraction may be significant. As compared with transforaminal lumbar interbody fusion and posterior lateral fusion, there has been greater reports of dural tear, epidural fibrosis, nerve root injury, and chronic arachnoiditis.

Although more recent advances, such as transforaminal and direct lateral approaches to the disk space, have decreased the frequency in which PLIF is performed, PLIF remains an important staple for spine surgeons.

Surgical Indications

The literature still supports surgeon preference in regard to interbody fusion and its indication whenever a lumbar fusion is performed. The argument that the intervertebral space is biologically and mechanically superior for fusion compared with the intertransverse space because of its larger surface area of highly vascular bony endplate and because the interbody bone graft is subject to compressive forces, is a controversial one. Despite those theoretic advantages and the avoidance of large amounts of muscle damage that occur from exposure for posterolateral fusion, it has been difficult to show clinical superiority of interbody fusions over posterolateral fusions for most lumbar degenerative pathology. Most published studies comparing the techniques reveal similar outcomes regardless of what fusion technique is performed. That being said however, there are certain circumstances when interbody fusion offers definite advantages, such as adding an interbody fusion to a posterolateral fusion which has been shown to increase the rate of achieving successful arthrodesis. Additionally, placement of an interbody graft at the anterior column allows for restoration of optimal disk height and therefore maintenance or improvement of segmental lordosis and optimal sagittal balance.

Some authors have argued that interbody fusion should be combined with posterolateral fusion in patients at high risk for failed fusion, such as smokers. For patients with pseudoarthrosis after failed posterolateral fusion, an interbody technique is a good salvage operation to augment revision procedures. In patients with isthmic spondylolisthesis who undergo deformity reduction, it has been well documented that an interbody graft offers a biomechanical advantage, which protects pedicle screw instrumentation with an anterior load sharing graft and aiding in maintenance of alignment. Controversially, the procedure may be used in augmenting the ablation of the disk space in patients with discogenic pain with the thought process being only interbody fusion can completely remove motion at a painful disk and the nuclear material resection may eliminate the anatomic source of pain. It is known that the outer annulus is richly innervated with nociceptive fibers and that mechanical deformation or inflammation caused by a damaged nucleus can stimulate these nociceptors. One thought is that although posterolateral fusion can increase axial stiffness by 40%, interbody fusion can increase axial stiffness by 80% to minimize any micromotion even further and reduce any nociceptive stimulation of sensitized painful disks. Lastly, interbody fusion by technique allows for removal of much disk tissue along with any nociceptors involved in the generation of pain.