Endoscopic Lumbar Interbody Fusion

Introduction

Since the early 20th century, spinal fusion has been performed as a therapy for both traumatic and degenerative disorders of the spine. Lumbar interbody fusion (LIF) in particular has proved an effective therapy for a variety of conditions, improving patients’ activity and quality of life. As the field of neurosurgery advanced, new and better surgical approaches were developed to reduce the morbidity and complications associated with this procedure. Of the major LIF approaches today, the transforaminal lumbar interbody fusion (TLIF) is one of the least invasive paths to the spine, avoiding several potential pitfalls of other LIF techniques.

The TLIF has enjoyed increasing popularity since the 1990s, in particular as a minimally invasive surgery (MIS) procedure. However, even though the MIS-TLIF bypasses the abdominal structures at risk with an anterior approach (ALIF) and the neural stress seen in a posterior approach (PLIF), it still requires an open muscular dissection, and thus faces the complications of any open procedure. Therefore, there have been efforts to further reduce the surgical trauma and exposure of the MIS-TLIF.

To this end, an endoscopic lumbar interbody fusion (endoLIF) protocol is described here. This chapter details the indications/contraindications, surgical technique, outcomes, and postoperative care of patients undergoing this procedure.

Indications

The indications for the endoscopic fusion are largely those of a typical open or MIS-TLIF, but there are subtle variations ( Table 15.1 ). Major indications include degenerative disease of one or two levels, spondylolisthesis, recurrent herniation, and spondylosis. The reduced blood loss, reliance on anesthesia, and recovery time also widen the patient population to include the elderly, and those with severe comorbid conditions that might otherwise preclude surgery. As the TLIF approach involves less neural retraction, these procedures can be performed at or above the level of L2, the site of the conus medullaris. This approach is also useful for revision of a prior PLIF, as there will be limited involvement of the previous entry site and scar tissue.

TABLE 15.1

Indications and Contraindications for Endoscopic Fusion

Indications	Contraindications
1. Major indications: • Degenerative disk disease • Spondylolisthesis • Recurrent disk herniation • Spondylosis • Lumbar deformity 2. Specific indications: Can be performed at or above L2 Revision of prior PLIF 3. MIS benefits: • Reduced blood loss • Reduced anesthesia • Reduced recovery time	1. Relative contraindications: • Conjoined nerve root • Severe canal stenosis • Severe osteoporosis 2. Anatomic considerations: • Neuroforamen size • Geometry of disk herniation • Iliac crest orientation

MIS, Minimally invasive surgery; PLIF, posterior lumbar interbody fusion.

Relative contraindications include severe bilateral or central canal stenosis, osteoporosis, and anomalous congenital nerve root fusion. Each patient’s unique anatomy and pathology must also be weighed in choosing a procedure, including considerations of neuroforaminal size, the geometry of any disk abnormality or herniation, and the size and location of the iliac crest relative to the target level. These anatomic factors can limit the surgical access of the endoLIF approach.

Limitations

The development of modern endoscopic instruments and the continuous demand by patients for improved postoperative recovery have resulted in a robust advancement in the realm of endoscopic spinal surgery. To date, established experiences in the literature include far lateral disk herniation, lumbar reherniation, spondylolisthesis (no more than grade II), discogenic pain, and spinal tumors. Some surgeons have found that the merits of endoscopic surgery in the lumbar spine could be better appreciated in the treatment of patients with severe obesity and advanced age.

The endoscopic lumbar spinal procedure adopted by most surgeons is the oblique transforaminal approach. Given that the greatest difference between endoscopic surgery and nonendoscopic surgery is the method of visualization (i.e., 2D vs. 3D); more deformed or degenerative changes in Kambin’s area increase the difficulty and technical demand of the procedure. Even though there has not been an established contraindication to this procedure, it has been generally agreed that patients with spondylolisthesis more than grade II, and patients with severe scoliotic changes or rotatory deformity at the indicated levels may not be good candidates to undergo endoscopic spinal fusion surgery.

Limitations also exist when the surgical neuroanatomy contradicts the accessibility created by the utmost minimally invasive spinal procedure. With the transforaminal approach, removing a centrally located pathology is more challenging, but can be managed with an interlaminar approach. However, this may not be the case if the herniated disk has significant cranial or caudal migration. It has been suggested that the herniated disk may not be managed with an endoscopic procedure if it extends below the mid-pedicle level caudally, or up to the inferior edge of the pedicle cranially.

Another challenging condition is advanced spondylosis. At any level, an enlarged facet or superiorly deformed superior articular process may block the placement of endoscopic instruments to the disk. Sometimes this can be managed by using endoscopic drills, osteotomes, or adjusting the entering angle. In extreme cases, however, deformity of the structure in the foramen and facet above the 2D visualization may lead to less optimal surgical outcomes.

High rising iliac wings can also be problematic, especially when targeting lower lumbar disk levels. In a publication by Yue and Long, it is suggested that the superior border of the iliac shadow should not be more proximal than the middle level of the pedicle above the indicated disk on lateral fluoroscopy. Male patients undergoing endoscopic procedures at the level of L4-5 or L5-S1 deserve special consideration, as male anatomy tends toward a more steep and upright pelvic structure.

Surgical Procedure

Anesthesia

The minimally invasive endoscopic LIF can be done when the patient is under general anesthesia or local analgesia with conscious sedation. The main advantages of general anesthesia include a better protection of the airway and less restriction of operative time. Conscious sedation offers greater interactive feedback from the patient, thus reducing the risk of jeopardizing neural structures.

Positioning

The patient can be in the prone position, although some surgeons prefer to use lateral positioning. There are a few advantages in utilizing lateral positioning, including reduced abdominal and venous pressures, less airway stress for the patient, and better interaction with the patient in case of an awake procedure. The downsides of lateral positioning are less familiarity of anatomic orientation and increased operative time for positioning.

It is recommended to utilize an operating room table that contains a four-point support system (e.g., Jackson table, Allen table) if the procedure is done with general anesthesia. The purpose is to obtain a better lumbar lordotic curvature once the fusion is completed. However, for patients undergoing awake procedures, the four-point support frame commonly leads to patient insecurity with less comfort. In that case, an arched frame (e.g., Wilson frame) may be utilized. In the setting of an awake procedure, transparent surgical draping is very useful for better monitoring and communication with the patient ( Fig. 15.1 ). Care should be taken to lower the Wilson frame to minimize lumbar flexion.

Skin Incision

In the transforaminal approach, the goal is to access the indicated disk through the Kambin’s triangle from the lateral aspect of the facet ( Fig. 15.2 ). The skin incision is marked 6 to 12 cm paramedian to the midline. The Kambin’s triangle is formed by the three borders: the exiting nerve root (the lateral border), the lateral margin of the traversing nerve root (the medial border), and the upper endplate of the lower vertebra (the caudal border). It has been generally agreed that the safety triangle ranges from L1-2 to L4-5 levels, based on cadaveric measurements. There are several ways to determine the paramedian length between the incision and the midline. Arbitrarily, it is suggested to make the incision 9 to 11 cm lateral to the midline, although several methods have been proposed in the literature. Some surgeons prefer to measure the length on preoperative computed tomography (CT) scans or magnetic resonance imaging, others advocate more specific intraoperative measurement based on fluoroscopy, in which they measure the distance from the center of the indicated disk to the skin surface on lateral view and adopt this distance as the paramedian length. Whatever method is utilized, it is generally recommended that the skin incision should not exceed ventrally to the posterior facet line shown on lateral fluoroscopic view, to avoid jeopardizing the peritoneal structures. The angle of surgical trajectory in the coronal plane ranges from 25 degrees to 35 degrees, depending on the procedure level and the anatomic location of the pathology (i.e., intraforaminal vs. extraforaminal; central, lateral vs. far-lateral).