Chapter 170 Transforaminal Lumbar Interbody Fusion

Indications and Techniques

Lumbar fusion is an accepted treatment for spinal deformity, iatrogenic instability following decompressive procedures, and more controversially refractory axial back pain caused by degenerative disease of the spine.¹ Lumbar interbody fusion yields certain advantages over posterolateral fusion alone, particularly because of higher rates of fusion.² Segmental motion still exists with posterolateral fusion alone, but this motion is significantly reduced with fusion techniques through the intervertebral disc space.^3,4 Biomechanically, the disc contributes significantly to anterior column stability, and the stabilizing influence of a posterolateral fusion depends on an intact anterior column.⁵ Transforaminal lumbar interbody fusion (TLIF) reestablishes anterior column support while allowing for posterior fixation, thereby imparting improved fusion rates because of circumferential support.⁶ Furthermore, as an interbody technique, TLIF helps restore disc and foraminal height and promotes lumbar lordosis.⁷ TLIF obviates the morbidity from the retroperitoneal dissection and subsequent posterior fixation required from anterior lumbar interbody fusion (ALIF). And unlike posterior lumbar interbody fusion (PLIF), TLIF requires minimal to no retraction on the thecal sac and nerve roots while still providing 360 degrees of support. In addition, because TLIF utilizes a more lateral trajectory, it can be performed in the setting of previous surgery with identifiable landmarks and a cleaner plane of dissection.

Surgical Technique

In general, TLIF utilizes an imagined quadrangular space between the transverse processes of the vertebral bodies adjacent to the affected disc space and the traversing nerve root medially (Fig. 170-1). Both open and minimally invasive techniques are utilized. The open technique is described stepwise, followed by modifications for the minimally invasive procedure.

FIGURE 170-1 TLIF utilizes an imagined quadrangular space between the transverse processes of the vertebral bodies adjacent to the affected disc space and the traversing nerve root medially. A, Working space for a TLIF. P, pedicle; TP, transverse process; T, thecal sac; hatch marks, disc space. B, Intraoperative view of exposure necessary for a right-sided TLIF. D, disc space; N, exiting nerve root under P.

Positioning

A Foley catheter, sequential compression devices, and stockings are placed on the patient. Depending on the surgeon’s experience, autologous blood and a cell saver can be available. The patient is placed in prone position on a radiolucent frame. Use of a Jackson table allows decompression of the abdomen to decrease epidural bleeding. Positioning of the patient is performed to facilitate encouragement of lordosis. Fluoroscopy or plain films are used to localize the affected level.

Exposure

A midline incision is extended to the dorsal lumbar fascia over the identified disc space. A subperiosteal dissection is performed past the facet joints and to at least the base of the adjacent transverse processes on the side of the decompression and bone grafting. A bilateral exposure may also be performed as a variant of a PLIF operation.

Decompression

Depending on the compressive pathology, a laminectomy, facetectomy, or both are performed. Usually, a high-speed drill and osteotomies are used to remove the facet complex and unroof the neural foramen. Varying amounts of the pars interarticularis can be removed for better visualization of and access to the disc space. The bony decompression is pedicle to pedicle. The surgeon should identify the exiting nerve root passing under the superior pedicle and lateral to the disc space, as well as the medial traversing nerve root. Only minimal retraction is required on these elements, and they are identified to avoid injury.

Pedicle Screw Placement and Disc Preparation

We prefer to cannulate the pedicles prior to disc space preparation but do not place ipsilateral screws until after the intervertebral work is completed. The majority of the blood loss during the case occurs during the preparation of the intervertebral disc, and it is efficient to have the cannulation completed in advance. Screw heads may obscure the view of the disc space, however, so the ipsilateral screws are not placed until after the intervertebral graft has been placed. The pedicles are cannulated under direct visualization using previously described anatomic features. The pedicle screw sites are always confirmed with fluoroscopy. An aggressive discectomy is performed, with the surgeon carefully staying within the bounds of the annulus to avoid potential vascular injury. Sequential disc space distractors are used to open the disc space, facilitating further disc removal. The end plates are assiduously scraped to remove the cartilaginous end plate, with the surgeon carefully preserving the bony end plate. The posterior lip of the vertebral bodies must be removed to attain more direct access to the disc space. Distraction is achieved within the disc space. Once final distraction has been achieved, it may be maintained through the use of a temporary rod in the contralateral screws as a distraction device. We prefer to pack locally harvested autograft into the prepared disc space prior to placing the structural graft.

Interbody Fusion

Various options are available for the structural graft. The many commercially available cages come in a variety of sizes and shapes and are designed to be filled with morselized bone or other graft substitute. We prefer structural allograft; however, excellent results have been reported with a variety of constructs. Some authors advocate placing two smaller cages sequentially in the middle column—this strategy makes manipulation of the cages easier and takes advantage of the stronger end plate near the periphery of the disc space. Our technique has changed somewhat, and larger, more anteriorly placed grafts are now preferred. Bone graft is packed anteriorly and to the contralateral side. Bone graft substitutes or adjuvants such as bone morphogenetic protein 2 have been described as a means to facilitate fusion. Bone graft extenders such as hydroxyapatite or beta-tricalcium phosphate may also be used. Once the graft is in place and checked with fluoroscopy, the temporary distracting rod is removed. Ipsilateral pedicle screws are placed, and compression is placed across the heads of the screws to induce lordosis and to lock the graft in place. The wounds are closed in multiple layers, and no external orthosis is necessary.

Minimally Incisional TLIF

Because of its posterolateral approach, TLIF is amenable to minimally incisional techniques. Minimal-access TLIF requires less tissue retraction and avoids the harmful effects of prolonged muscle retraction on truncal strength and postoperative back pain.^8,9 There is also less blood loss with the technique.¹⁰ Anecdotally, after the initial learning curve, we found the minimally incisional version of this procedure easier and faster to perform, and the large dissection required for the open procedure is skipped.

Modifications from the previously described open approach lie mainly in exposure and fixation. The incision is paramedian, approximately 4 to 5 cm off the midline and lateral to the pedicular line. Review of the preoperative magnetic resonance image may reveal an intermuscular septum that may be exploited to expose the facet joint with virtually no muscle dissection. Fluoroscopy is used to center the incision over the disc space to be fused. The incision is carried to the dorsal lumbar fascia. The fascia is opened, and finger dissection is used to identify the facet. Multiple tubular or bladed retractor systems are available to facilitate exposure. Some employ the use of sequential soft-tissue dilators (e.g., METRx, Medtronic Sofamor Danek) to expose the overlying facet complex. With this system, a 20-mm working channel is necessary for placement of an interbody graft.¹¹ The system we advocate takes advantage of the fascial interval between the longissimus and the iliocostalis (erector spinae) muscle bellies at the level of the tips of the transverse processes.⁷ Blunt dissection is performed in this avascular plane to the facet complex and transverse processes (Fig. 170-2). A ventral cervical retractor system (e.g., Black Belt, T. Koros Surgical Instruments) is utilized to maintain exposure (Fig. 170-3).

FIGURE 170-2 Axial T2-weighted magnetic resonance imaging scan of the lumbar spine, demonstrating the fascial interval between the longissimus and the iliocostalis (erector spinae) muscle bellies. Blunt dissection performed in this plane reveals the tip of the transverse process and medially the facet complex.

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