Posterior Lumbar Interbody Fusion for Degenerative Disorders of the Spine

CHAPTER PREVIEW

CHAPTER SYNOPSIS:

Interbody fusion is often the surgical treatment of choice for degenerative spine disease. Posterior lumbar interbody fusion (PLIF) was developed originally but was associated with neural retraction injuries. Thus, this technique was modified into the transforaminal lumbar interbody fusion (TLIF), which minimizes neural retraction. This chapter reviews the indications for interbody fusion and discusses the techniques for PLIF, open TLIF, and mini-open TLIF.

IMPORTANT POINTS:

Indications
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Degenerative disc disease
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Spinal stenosis
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Segmental spinal instability
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Bilateral disc herniation
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Recurrent disc herniation
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Spondylolysis and spondylolisthesis
Limitations
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Traditional PLIF requires excessive dural sheath retraction, which can lead to neural injury.
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TLIF procedures may be inadequate to treat patients with severe osteopenia because this can lead to end plate disruption and implant subsidence.
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Narrow stiff disc spaces and kyphotic deformities may be better suited for anterior lumbar intervertebral fusion than TLIF.

CLINICAL/SURGICAL PEARLS:

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After the initial approach, the pedicles are prepared, and pedicle screws are used for distraction to access the intervertebral disc space.
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The disc space is prepared by removing all disc material.
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Spacers are used to allow positioning of the implant, structural bone graft, or both.
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Patients with kyphosis are better corrected with anterior interbody fusion.
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Adult patients with deformity who require multiple levels may be best treated with combined anterior-posterior multilevel fusion as opposed to PLIF or TLIF in attempt to reduce the operative time and related risks.

CLINICAL/SURGICAL PITFALLS:

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If a conjoined nerve root is discovered, a contralateral side approach may need to be attempted; if the condition is bilateral, an anterior or anterolateral approach may be necessary.
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Avoid violation of the end plate by cutting the cartilaginous end plate in a trajectory parallel to the disc space.
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Osteopenic patients are at risk for end plate fracture from distraction, and these patients may require a simple posterior decompression and posterolateral fusion.
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Care must be used regarding instrument depth during interbody decompression and clearing the disc to avoid anterior vascular injury.

VIDEO AVAILABLE:

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Degenerative spine pathologies are diverse and may seriously affect the quality of life of the affected individuals, and degrade their functional level. Interbody fusion has been widely used as a surgical treatment for severely affected individuals who are not responsive to nonsurgical treatment options.

In 1953, Cloward described the posterior lumbar interbody fusion (PLIF) technique using a facet-sparing laminectomy. However, neural retraction injuries have been a problem with the traditional PLIF; thus, a modified technique called transforaminal lumbar interbody fusion (TLIF) has been developed to minimize neural retraction and provide a wide corridor for interbody decompression and fusion. In addition, the TLIF technique allows preservation of much of the normal anatomy including the supraspinous and interspinous ligamentous complex, lamina, contralateral facet, and contralateral ligamentum flavum. In addition, TLIF is appealing because it produces less epidural scarring and dural tears, and because it is always used with instrumentation, has a lower risk of postoperative instability.

INDICATIONS AND LIMITATIONS

PLIF has been described in the past as an ideal treatment for a wide variety of lumbar spine pathologic conditions, including degenerative disc disease, spinal stenosis, segmental spinal instability, bilateral disc herniation, recurrent disc herniation, spondylolysis, and spondylolisthesis. Unobstructed intervertebral disc exposure in traditional PLIF necessitates retraction of the dural sheath toward the midline. Generally, this is applicable only to the L3-4 level and more caudal segments because the position of the conus medullaris above L3 could be injured with vigorous retraction.

In contrast, the TLIF can be performed at all levels of the lumbar spine with similar indications to the PLIF but a lower rate of complications. However, TLIF procedures may not be the treatment of choice in patients with severe osteopenia in whom disc space distraction may result in end plate disruption and subsidence of the interbody implant. In addition, patients with a narrow and stiff disc space together with kyphotic deformities of the lumbar spine may best benefit from an anterior lumbar intervertebral fusion rather than TLIF. The adult deformity population also presents a challenge to the TLIF approach because multiple levels of disc space reconstruction are required, and this can become a time consuming and arduous task. More recently, minimally invasive TLIF procedures have gained in popularity but have a steep learning curve with as yet unproven results.

SURGICAL TECHNIQUE

Posterior Lumbar Interbody Fusion

A posterior midline approach is performed to expose lateral to the tips of the transverse processes of the level in question. After pedicle preparation, pedicle screws are inserted and distraction is applied through the screws to improve the access to the intervertebral space. Lamina and spinous processes are harvested, and midline decompression from pedicle to pedicle is used to expose the nerve roots and create the working zone. To limit the amount of retraction required to access the interbody space, a generous portion of the medial facet should be excised bilaterally. The dural sac and traversing nerve roots are carefully retracted medially to expose the disc space, and an annulotomy lateral to each side of the retracted dura is performed sequentially. Curettes and pituitary rongeurs are used to evacuate the disc material, and a bone chisel is used to decorticate and trim the vertebral end plates flush with the central concavity of the disc space. Maintaining disc space distraction using a unilateral disc space dilator, the surgeon then places an interbody cage or structural graft on the contralateral side. Next, the disc space dilator is removed and a second interbody cage or structural graft is applied to the ipsilateral side. The remainder of the disc space is filled with cancellous bone graft or a suitable substitute. The lumbar lordosis is re-established by compressing across the pedicle screw construct. The soft tissues are then reapproximated and the incision is closed. Some surgeons opt to use a closed suction drain.

Open Transforaminal Lumbar Interbody Fusion

A posterior midline approach is performed to expose lateral to the tips of the transverse processes of the level in question, respecting the integrity of supraspinous and interspinous ligaments ( Fig. 22–1 ). The pedicles are prepared and screws are placed in the surgeon’s preferred fashion. Access to the disc space is then achieved by resecting the pars interarticularis and performing a complete facetectomy at each level of the spinal segment to be fused. Skeletonization of the pedicle of the inferior level helps allow wide access to the disc space. The side of the facetectomy is generally chosen to address the worse leg symptoms of the patient because the exposure yields excellent decompression of both the exiting and traversing nerve roots. Interbody distraction can be facilitated using disc space dilators or by distracting the spinous processes or pedicle screws.

The “triangular working zone” is defined by identifying the lateral border of the thecal sac, the exiting nerve root, and the superior aspect of the caudad pedicle. This produces a safe working corridor through which intervertebral disc decompression and fusion are performed. This zone is immediately superjacent to the pedicle ( Fig. 22–2 ). Attention is paid to preserving perineural fat around the exiting nerve root, which ensures that irritation of the root and ganglion is avoided, which can lead to postoperative neurogenic pain. Small foraminal veins found in the inferior portion of the neural foramina and overlying the disc may need to be divided and cauterized to expose the disc. A rich vascular plexus also is consistently medial to the pedicle and requires cauterization before discectomy. A nerve root retractor is used carefully to protect the thecal sac and further expose the working zone for the disc space preparation ( Fig. 22–3 ). After a posterolateral annulotomy, the working channel is created by excising the exposed disc from the lateral border of the thecal sac to the lateral aspect of the disc space. A complete discectomy is then performed using a variety of pituitary rongeurs, single- and double-angled chondrotomes and curettes, and disc shavers ( Figs. 22-4 and 22-5 ).