360° Endoscopically Assisted Minimally Invasive Transforaminal Lumbar Interbody Fusion

22 360° Endoscopically Assisted Minimally Invasive Transforaminal Lumbar Interbody Fusion

Alvaro Dowling, Sebastián Casanueva Eliceiry, Gabriela C. Chica Heredia, and Jonathan S. Schuldt

22.1 Introduction

In recent years it has become a common trend in most spinal surgery units to seek minimally invasive and effective solutions. Initially, due to the learning curve, the results of minimally invasive surgery (MIS) were similar to those of conventional surgery, presenting some complications.1,2 Subsequently, after investment in the development of MIS surgery, it has become common and with significant casuistry. Nowadays the results of both types of interventions are similar, but it is important to mention that MIS presents lower complication rates.^3,4 Minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) has no significant disadvantages when compared with open TLIF or other standard lumbar fusion techniques.⁵ Recent studies have shown that the risks of blood loss, narcotic administration, pseudarthrosis, and infection all decreased when MIS-TLIF was used.⁶ Various postoperative recovery and pain rating scales often showed consistent improvement.⁵

The combination of MIS with the endoscope allows direct visualization of important anatomical structures and release of nerve roots from compression or adhesions. Also, it is possible to create enough space for cage placement in the intervertebral space by performing a foraminoplasty, which is especially relevant for the L5–S1 level.

We add biological therapy to increase the patient’s intervertebral fusion, combining three essential pillars for the procedure: BMC (stem cells), PRP (platelet-rich plasma and its growth factors), and bone allograft (Fig. 22.1). This approach obtains an increased percentage of somatic fusion.^7,8

With MIS endoscopically assisted TLIF, generally one to three levels can be fused, and occasionally four, depending on the anatomy of the patient.^9,10

22.2 Preoperative Planning

For preoperative imaging, the authors prefer to use MRI and sitting-standing dynamic X-rays (Fig. 22.2, Fig. 22.3). When feasible, we use CT, since it is more accurate for assessing the size of bony structures. Neutral X-ray (Fig. 22.4) provides information about alterations of physiological curvatures of the spine. Anatomical structures to consider include:

1. Vertebral pedicle: Pedicles are measured in their diameter, length, and orientation. Axial and sagittal views are necessary for accurate measurement (Fig. 22.5). This is relevant for planning screw placement.

2. Facet joint: The orientation of the facet joint is important when transfacet screws are being utilized (Fig. 22.6).

3. Spinal stenosis: Stenosis can be anatomically classified as central and lateral. Lateral stenosis is subdivided into lateral recess, medial, and foraminal (Fig. 22.7).^11,12 The decompression is planned according to the type of stenosis.

Fig. 22.1 Biologic pillars. A structural base, cells, and growth factors are needed for optimal soft tissue repair and intervertebral fusion.

Fig. 22.2 Extension dynamic X-ray, showing significant instability.

Fig. 22.3 Flexion dynamic X-ray, showing significant instability.

Fig. 22.4 Neutral X-ray, showing no significant instability.

Fig. 22.5 Axial and sagittal MRI. Pedicle length, diameter, and orientation are analyzed during preoperative planning.

Fig. 22.6 Facet angle. A greater α angle makes transfacet screw placement more difficult.

Fig. 22.7 Canal stenosis classification: 1, central stenosis, 2, lateral recess stenosis, 3, foraminal stenosis, and 4, extra foraminal stenosis.

Fig. 22.8 Iliac crest anatomy is studied in the preoperative planning. If a high iliac crest is combined with a large facet joint and a horizontal L5–S1 disk, the transforaminal approach has to be reconsidered.

Considerations for the L5–S1 level include:

1. Iliac crest: A high iliac crest can obstruct trocar passage to the L5–S1 disk. Occasionally, a wide ilium opening angle (evaluated preoperatively) allows access to this level (Fig. 22.8).

2. Disk obliquity: A horizontal disk will present more difficulty in placement of an intersomatic cage. A sagittal imaging view is employed to assess obliquity (Fig. 22.9).

3. Facet size: Larger facets may require a manual foraminoplasty with a trephine if the trocar is unable to reach the intervertebral disk. Manual drills may also be utilized. Once the endoscope can access the neuroforamen, a bur drill can expand the area, releasing the exiting nerve root from compression and allowing the surgeon to reach the intervertebral space.

In our experience, when preoperative planning is performed thoroughly, complications and surgical times are significantly improved.¹³ With a sterilized marker and with the help of the C-arm, the midline is traced following the spinous processes, 8 to 12 cm from which are marked laterally on the skin (Fig. 22.10). Intervertebral spaces are marked on a lateral and posteroanterior (PA) view. In a PA view, we mark the affected level after lordosis has been corrected by tilting the C-arm. Vertebral pedicles are also marked. In a lateral view, we mark the obliquity of the disks.

Fig. 22.9 Disk obliquity is especially relevant when a high iliac crest is present.

Fig. 22.10 Preoperative landmarks. L4–L5 and L5–S1 are marked on PA and lateral views.

Fig. 22.11 Operating table and different components of the operating room.

22.3 Position and Anesthesia

The evolution of spinal surgery technology has helped improve other fields of medicine. New techniques in anesthesia have been developed to aid with monitoring and better outcomes for the patients. It is the authors’ and the anesthesiologist team’s preference to use a continuous infusion of dexmedetomidine and propofol, to obtain conscious sedation under monitored anesthesia care (MAC).14 When the correct sedation state is achieved, the surgeon can perform procedures using local anesthesia and, indeed, achieve adequate anxiolysis and analgesia for the patient.^15,16,17,18 Two-percent lidocaine is used to provide local anesthesia in the skin, while 1% lidocaine is used in the entire intramuscular working tract.

Surgeons cannot get a more accurate response (physically and verbally) than from the awake patient.

Because of the continuous neuromonitoring, complications can be diminished and success rates improved. Although the patient can speak up if there’s a problem, the anesthesiologist is always checking for changes in vital signs. Several studies have supported the alliance between MIS and this anesthetic method.¹⁸

The patient is placed in the prone position with slight flexion of the spine. A specially designed operating table is used to improve surgical performance, allowing the C-arm to freely move under and above the table. Also, there is an empty space designed to receive the patient’s abdomen. This reduces intra-abdominal pressure and therefore decreases bleeding, due to proper drainage of the Batson plexus.¹⁹ C-arm fluoroscopy is placed contralateral to the operation site (Fig. 22.11, Video 22.1).

22.4 Posterior Decompression

In cases with central spinal stenosis, the surgery starts with central decompression, with placement of progressive dilators and tubular retractors up to 13 mm directly onto the pedicle (Fig. 22.12). Decompression begins with a proximal hemilaminectomy, then a complete facetectomy followed by a distal hemilaminectomy. Dissection of the ligamentum flavum is performed to achieve complete decompression of neural structures.

Due to the inverted cone effect (Fig. 22.13), where through a small incision we rotate and change our approach angle, we can use a single incision and obtain contralateral nerve root decompression by tilting the tubular retractors medially. Because of this advantage, we prefer not to fix the tubular retractors and to perform a free-hand technique (Fig. 22.14).⁹ In cases where symptoms are clearly bilateral, a contralateral approach with tubular retractors can be performed, although it is fairly rare.

Fig. 22.12 Surgical equipment for posterior decompression.

Fig. 22.13 Inverted cone. Left: Inverted cone effect, less soft tissue disruption and wide surgical area through a small incision. Right: Open approach, soft tissue damage by retraction, and smaller surgical area.

Fig. 22.14 Free-hand technique. This allows the surgeon to use both hands to freely move surgical instrumentation.

Fig. 22.15 Posterior view of a hybrid system. Left posterior decompression. Two pedicle screws on the left with bone allograft in the interpedicular area. One transfacet screw on the right.

Fig. 22.16 Manual foraminoplasty using drill bits.

Fig. 22.17 Manual foraminoplasty using a trephine.

Decompression is finalized when we are able to move the traversing nerve root with no associated pain. A posterior view of the spine after a left laminectomy has been performed is shown in Fig. 22.15.

22.5 Instrument Placement for the Posterolateral Approach

A standard dilation system is used to place a 7-mm working cannula for a 20° high-definition (HD) endoscope. The endoscope accesses the area at a 45° angle, and, depending on the patient’s size and fat tissue, the incision is made 8 to 12 cm from the midline.