Patient Selection

As with any operation, patient selection is a critical factor in lumbar spine surgery where preexisting pain syndromes and dependence on medication may complicate the pre- and postoperative care of patients. The rationale for performing a PLIF is that fusion of the vertebral segments eliminates any instability that may be causing recurrent or persistent pain. Unless a focal neurologic deficit is identified, aggressive nonoperative therapy, including but not limited to the use of muscle relaxants, steroid injections, and pain medications, should be tried prior to committing the patient to an operation. Contraindications to performing PLIF include osteoporosis, discitis, subchondral sclerosis, and adhesive arachnoiditis. Once a patient has been selected for surgery, standard preoperative imaging and laboratory tests, including electrocardiography and chest x-rays, should be obtained, and the patient should be cleared by anesthesia for operative intervention. In most cases, supine and standing radiographs and computed tomography of the spine may be useful.

Open PLIF

The classic PLIF technique consists of three surgical steps: (1) laminectomy or laminotomy with partial or complete facetectomy, (2) removal of the intervertebral disc, and (3) fusion. The classic PLIF technique is performed with the patient in the prone position, using a midline incision and subperiosteal dissection. Although the approach is relatively straightforward, the posterior spinal musculature is likely to be damaged. With the advent of minimally invasive spinal approaches (described later), many surgeons now use muscle-splitting approaches to minimize such damage to the paraspinal muscles.

After the patient is placed in the prone position, pressure points are padded to minimize pressure sores (Fig. 169-1). A Jackson table can be used to avoid compression and venous congestion, which may cause excessive bleeding during posterior approaches. Fluoroscopy should be used to identify the spinal level of interest. As in any posterior approach, the landmarks are the spinous processes, iliac crest, and posterior superior iliac spine.

FIGURE 169-1 Setup of the operative theater with the patient positioned prone, the fluoroscope and microscope in place, and the position of the anesthesia team and scrub staff relative to the surgeon.

(Used with permission from Barrow Neurological Institute.)

The skin is incised (Fig. 169-2A) in the midline above the spinous process, and the subcutaneous tissue is dissected. The thoracolumbar fascia is incised and dissection proceeds in a subperiosteal fashion, detaching the paraspinal muscles from the spinous process and lamina (Fig. 169-2B). For each level that is to be treated, the cranial lamina and ligamentum flavum are removed completely (Fig. 169-2C). The cranial aspect of the caudal lamina should also be removed to gain adequate access to the interbody space. To prevent traction on the spinal cord or nerve roots during placement of the interbody graft, a wide window is created by resecting the lower third of the inferior facet and the medial two thirds of the superior facet. Next, the nerve root and dural sac are retracted medially, creating maximal exposure of the interbody space for removal of any bony or disc material (Fig. 169-3A).

FIGURE 169-2 A, Incision used in the open PLIF centered over the thoracolumbar spine. B, The incision exposes the anatomy, revealing the lamina, facet joints, and dura. C, Next, the lamina and facets are removed and the exposure of the annulus and dura is increased to perform the necessary discectomy without placing undue traction on the spinal cord and thereby damaging it.

(Used with permission from Barrow Neurological Institute.)

FIGURE 169-3 A, The nerve root and dural sac are retracted medially, creating maximal exposure of the interbody space. B, The interbody device is inserted bilaterally and packed with bone for maximal fusion. C, A pedicle screw is used to distract the disc space. The trajectory and depth of the screw are important for successful fusion. D, Next, using either a screw or a rod construct, the final arthrodesis is reinforced until biologic fusion is achieved.

(Used with permission from Barrow Neurological Institute.)

Following adequate decompression of the neural structures and removal of the disc material, the disc space is distracted using pedicle screws or disc space distractors. We prefer to use pedicle screws as distractors (Fig. 169-3B). Next, the end plates are prepared, using curettes to remove any remaining disc material while preserving the bony end plates to prevent graft subsidence. Adequate preparation of the graft site and preparation of the end plates are important steps for ensuring a proper fusion.

In young patients, the lumbar cortical end plates are thinner; therefore, when a PLIF is performed on a young patient, appropriate exposure of the cortical bone is sufficient to ensure adequate surface for fusion. In older patients, the surface of the bone should be roughened to the cancellous bone to provide adequate blood supply for fusion.

Next, a graft spacer or cage is placed into the interbody space under direct visualization of the cranial and caudal nerve roots (Fig. 169-3C). Bone graft packing is used to augment the fusion. The graft choice is highly surgeon dependent, with options such as threaded cages, titanium mesh cages, and auto- and allograft with or without the use of bone morphogenetic protein. The graft-filled interspace is stabilized with internal fixation using screws and rods or a plate construct to aid in fusion and immobilization (Fig. 169-3D).

PLIF is an effective procedure and results in excellent fusion (Fig. 169-4) with rates in the range of 80% to 98%.^13,14 PLIF also has been shown to be effective for reducing pain and disability.¹³

FIGURE 169-4 (A) Posterior and (B) anteroposterior computed tomography scan of the final construct after an open PLIF.

(Used with permission from Barrow Neurological Institute.)

Minimally Invasive Spine PLIF

Minimally invasive PLIF is an alternative to the open technique described earlier. As is the case for open PLIF, the patient is positioned prone (see Fig. 169-1). Using fluoroscopic guidance, the correct level is identified. At the Barrow Neurological Institute, we use the METRx microdiscectomy system of endoscopic and microscopic tubular dilators, retractors, and a bed-mounted flexible arm. Once the correct level is identified, a small 2- to 4-cm incision is placed off midline (Fig. 169-5) at the appropriate level and a Steinmann pin is passed until it reaches the medial border of the facet joint. Next, the skin incision is extended 2 to 3 cm above and below the Steinmann pin, and serial dilators are used for muscle splitting (Fig. 169-6). Once adequate muscle splitting and visualization are achieved, the final channel is fixed to the flexible-arm retractor mounted to the table side rail and the sequential dilators are removed. Exposure, laminotomy, ligamentum flavum removal, and discectomy are then performed as described previously.

FIGURE 169-5 Incision used in the minimally invasive PLIF centered over the thoracolumbar spine.

(Used with permission from Barrow Neurological Institute.)

FIGURE 169-6 Dilator setup used for the muscle-splitting technique.

(Used with permission from Barrow Neurological Institute.)

After full decompression, attention is directed toward preparation of the end plates for eventual graft placement. First, the smallest of the interbody distractor device is placed into the disc space under direct visualization. The distractors are used to restore intervertebral height. Decompression of the contralateral side follows and is facilitated by placement of the interbody distracting devices. Once the disc space is prepared, the interbody graft is placed into the disc space and augmented with autologous bone graft. Additional graft is then packed around and within the remaining facet to augment fusion.

Next, a No. 11 Jamshidi needle is used to identify and cannulate the lumbar pedicles. After adequate visualization of the pedicle using fluoroscopy, the Jamshidi needle is used to perforate the dorsolumbar fascia down to the level of the pedicle. The needle is tapped into place and gradually advanced through the pedicles beyond the posterior margin of the main vertebral body. After the location of the needle is confirmed, the obturator is removed and a long K wire is exchanged through it.

Next, using sequential dilators, the screw path is defined, and a tap is passed coaxially over the K wire through the pedicle into the cancellous portion of the vertebral body. Multiaxial pedicle screws are attached to the screw extender sleeves and passed over the K wire through the previously tapped screw pathway. Precontoured rods are passed and lodged to the screws. Locking bolts on the screw heads are used to secure the rods in place. The locking bolts are tightened and released from the inserter.

Complications of PLIF

PLIF is a technically challenging and demanding procedure and consequently is associated with complications. Two of the primary complications of PLIF are nerve root injury and incidental durotomy related to the significant traction that must be placed on the thecal sac and nerve roots to gain access to the interbody space.¹⁵ The nerve root that exits at the level above the disc space often lies near the interbody graft as it is being placed and can easily be injured.One study reported an incidence of nerve root injury as high as 13%.¹⁶ Angled nerve root retractors and direct visualization of the nerve roots at all times can help prevent neurologic injury during the procedure. A more aggressive facetectomy can provide a more lateral approach, offering an excellent window for graft placement while minimizing retraction of the thecal sac. Dural tears can usually be repaired primarily but can be more difficult to repair when using the minimally invasive technique.

As is the case with any surgical operation, infection, bleeding, stroke, and death are other possible complications. Other PLIF and back surgery–specific complications include wrong-level surgery, adjacent-level disease, graft retropulsion, and pseudarthrosis in the case of instrumentation with PLIF.¹⁷ Frequent causes of graft retropulsion include inappropriate sizing of the graft, resulting in graft mobility; delayed fusion; and instability of motion segments, however, the rate of retropulsion is less than 2%.¹⁸

Conclusion

Since the first report of the PLIF, the technique has been modified and augmented to produce excellent rates of arthrodesis. With an extended application to pathologies as diverse as recurrent disc herniation, failed back surgery syndrome, spondylolisthesis, bilateral midline disc herniation, segmental instability, and degenerative disc disease, comfort with this technique, both as an open and as a percutaneous approach, is important for surgeons.