14.1 Introduction

Navigated minimally invasive transforaminal lumbar interbody fusion (TLIF) evolved from the posterior interbody technique. By utilizing a more lateral approach, TLIF allows access to the intervertebral disk while minimizing the need for neural retraction, decreasing the frequency of accidental durotomy and postoperative radiculitis. ¹ The addition of interbody arthrodesis to posterior fusion increases arthrodesis rates and potentially restores sagittal alignment. ^{2 ,​ 3}

Over the last two decades, there has been a trend toward minimally invasive surgery (MIS) when performing TLIF. Studies have consistently demonstrated that relative to open TLIF, MIS TLIF is associated with reduced blood loss, less postoperative pain, shorter hospital stay, less soft-tissue trauma, earlier mobilization, improved cosmesis, and decreased infection rates. ^{4 ,​ 5 ,​ 6} At the same time, MIS surgery has a steep learning curve and significantly higher radiation exposure than open surgery. ⁷

Computer-assisted navigation (CAN) was introduced in spine surgery in the 1990s in an effort to improve surgical accuracy and reduce radiation exposure. ⁸ CAN systems combine intraoperative three-dimensional (3D) fluoroscopy or cone-beam computed tomography (CT) with real-time precision instrument tracking to allow 3D stereotactic guidance. Navigation expands on the promise of MIS by decreasing radiation exposure, improving accuracy, and potentially easing the MIS learning curve. ⁹

14.2 Indications

Indications for navigated MIS TLIF are similar to open TLIF, ¹⁰ which include spondylolisthesis with associated stenosis or mechanical back pain, recurrent disk herniation, foraminal stenosis or a synovial cyst which cannot be safely addressed without destabilizing the facet joint, pseudarthrosis, and postlaminectomy kyphosis or instability. ^{6 ,​ 10 ,​ 11} Navigation is particularly useful in cases where visualization is compromised, anatomy is distorted, or safe implant corridors are limited. For example, navigation is beneficial in cases of obesity, oncology, revision surgery, complex deformity, pediatric surgery, iliac fixation, and cervical or thoracic pedicle screw placement. ^{6 ,​ 12}

14.3 Contraindications

There are few absolute contraindications to TLIF except active local infection. Relative contraindications include systemic infection, aberrant anatomy such as a foraminal conjoined nerve root, severe spondylolisthesis, spinal metastases, acute fracture, extensive scarring, severe osteoporosis, or ankylosis of the affected level. ^{10 ,​ 13} Wound healing risk factors such as poor nutritional status or diabetes mellitus should be optimized; however, if surgery is necessary, MIS may provide a more appropriate option due to limited wound size. ¹³ Metallic implants from previous surgery may distort imaging and make MIS unsafe or navigation inaccurate. Multilevel surgery may be technically more challenging to perform with an MIS technique. Unlike posterior lumbar interbody fusion, TLIF can be performed in the lumbar spine at the level of the conus; however, injury to neural structures in the upper lumbar spine remains a concern. Interbody fusion for diskogenic back pain has not shown significantly better outcomes than nonoperative management ¹⁴ and surgery should be carefully considered in this population. Patients with impaired ability to follow postoperative restrictions may not be appropriate for operative intervention.

14.4 Preoperative Planning

A thorough history and examination is mandatory in all patients. Particular attention should be paid to the side of most prominent radicular symptoms, as this will dictate the side of the TLIF approach. Patients without emergent findings should have symptoms refractory to at least 3 months of conservative management prior to surgical consideration.

Anteroposterior and lateral radiographs of the lumbar spine are used to evaluate sagittal and coronal alignment, extent of disk disease, and bone quality. Sagittal flexion and extension radiographs can reveal dynamic instability. Comparing standing plain films to supine imaging such as CT or magnetic resonance imaging (MRI) may also reveal subtle instability. MRI is used to confirm the diagnosis, plan surgery, and assess neural anatomy. CT myelography is ordered if MRI is contraindicated. CT can help distinguish bony neural compression from soft-tissue pathology and help plan implant size, type, and position. The CT scan should be optimized for the planned CAN system if preoperative fine-cut CT scan is required.

A surgical plan should be formulated preoperatively and all members of the surgical team should be briefed. A preemptive multimodal analgesia regimen is administered in the preoperative holding area ¹⁵ and antibiotics are administered prior to incision.

14.5 Operating Room Setup and Positioning

Deliberate operating room (OR) preparation is critical for safe and efficient surgery. A large OR is helpful to accommodate the imaging unit, surgical microscope, and navigation system including cameras and monitors (Fig. 14‑1). The patient is positioned prone on a radiolucent table such as a Jackson cradle which allows preservation of lumbar lordosis. The abdomen hangs free to prevent venous congestion and pressure points are well padded. The anesthesiologist should be instructed to turn the head frequently to decrease pressure on the face. When working in the lower lumbar spine, a reverse Trendelenburg table position decreases forces on the face and chest while allowing a more vertical trajectory for pedicle screws and disk preparation. The patient is secured to the bed with tape which helps decrease patient movement and increase navigation accuracy. For CT scanning–based CAN, the scanner is typically positioned at the patient’s head with leads, cords, and suction tubes extending cephalad through the gantry. Neuromonitoring is initiated prior to transferring the patient prone; changes in somatosensory evoked potentials and motor evoked potentials after flipping may indicate a need to adjust positioning.

14.6 Registration and Localization

Navigation systems require registration of the patient’s bony anatomy with the system’s 3D anatomic reconstruction. After standard sterile draping, the operation begins by embedding the reference array firmly in the posterior superior iliac crest through a stab incision. The navigation camera is then registered with the reference array and surgical instruments are calibrated. At this time, most CAN systems utilize an intraoperative scan to register patient position and reconstruct 3D anatomy. In CAN systems which utilized preoperative CT, coregistration is performed with fluoroscopy or bony point matching with a navigable probe.

14.7 Pedicle Preparation and Pedicle Screw Insertion

Posterior pedicle screw instrumentation supports the interbody construct. Incisions should be planned using a navigable probe to mark pedicle trajectories on the skin. By confirming retractor and pedicle screw trajectories, a smaller and more accurate incision may be utilized, resulting in less skin retraction. The incision is located approximately 3 cm lateral to the palpable midline spinous processes at the disk level. Surgery generally follows the transmuscular paraspinal (Wiltse) plane between the multifidus and longissimus portion of the sacrospinalis muscles ¹⁶ ; however, dilator tubes invariably result in some muscle splitting. After the incision is made, the initial, navigable dilator is advanced to dock on the lateral facet in a trajectory coaxial with the pedicle and a K-wire is advanced into bone.

Pedicle screws may be placed before or after the TLIF. Placing screws prior to interbody work facilitates distraction between the screw heads, increasing visualization and easing insertion of the interbody device. However, pedicle screws may limit the working space during disk preparation and distraction may weaken pedicle screw fixation. If TLIF is to be performed first, wires are retracted out of the field.

When placing pedicle screws, sequential dilators are advanced over the K-wire until the final retractor is positioned and affixed firmly to the operative table. A navigable tap undersized 1 mm from the desired screw diameter is then used to cannulate the pedicle and is advanced into the vertebral body under live guidance. If electromyography neuromonitoring is being utilized, this tap may be stimulated to identify wall breaches in the pedicle. An appropriately sized pedicle screw is then placed with guidance.