LLIF L2/3/4/5

38 LLIF L2/3/4/5

Frank M. Phillips and Sravisht Iyer

Summary

The extreme lateral interbody fusion (XLIF) or lateral lumbar interbody fusion (LLIF) is a minimally invasive approach to fusion in the lumbar spine. LLIF can treat foraminal stenosis, moderate lateral recess stenosis, and degenerative scoliosis. Safely performing LLIF requires paying close attention to the neurovascular anatomy, identifying the lumbar plexus using EMG, and minimizing table break and retractor time. Close adherence to these principles can help minimize complications.

Keywords: lateral lumbar interbody fusion psoas anatomy EMG monitoring patient positioning lateral technique

38.1 Introduction

First described in 2006, lateral lumbar interbody fusion (LLIF) was developed as a minimally invasive, lateral, retroperitoneal trans-psoas approach to the lumbar spine.1 Since that time, the LLIF procedure has since been widely adopted as a method for placing anterior lumbar interbody devices in the lumbar spine.² This chapter discusses the most common indications and contraindications for this procedure. We also discuss surgical techniques, postoperative care, and tips and tricks that have been learned through the authors’ experience.

38.2 Indications

The United States Food and Drug Administration has only approved LLIF for one- and two-level lumbar fusions with supplemental posterior fixation.² However, clinically, the LLIF is frequently utilized, with or without posterior fixation (i.e., stand-alone),for multilevel pathology (e.g., in adult spinal deformity). Commonly practiced indications for LLIF include various lumbar degenerative pathologies (degenerative scoliosis, spinal stenosis, degenerative disc disease, adjacent segment degeneration) and adult spinal deformity (ASD).²

For lumbar degenerative disease, the LLIF has enjoyed success in achieving indirect neural decompression via disc space distraction in patients with mild to moderate lateral recess and central canal stenosis and/or moderate to severe foraminal stenosis.³ There is also considerable evidence to suggest that LLIF may be effective in treating patients with low-grade (Grade I/II) degenerative spondylolisthesis as well as degenerative scoliosis.⁴^,⁵^,⁶

LLIF aims to restore lumbar disc height via the use of an interbody biomechanical cage device. Compared to posterior approaches, LLIF allows for placement of a substantially larger interbody cage without the need for entry into the spinal canal or neuroforamen. This avoids the need for neural manipulation and retraction. Placement of these larger cages provides direct restoration of the foraminal height and indirect decompression of the spinal canal via stretching of the posterior longitudinal ligament (PLL) and unbuckling of the ligamentum flavum; increases in foraminal, central, and lateral recess area have been demonstrated on postoperative imaging.⁷^,⁸^,⁹^,¹⁰ LLIF in patients with foraminal stenosis has been shown to improve health-related quality of life (HRQOL) scores at up to 1-year follow-up.⁶^,⁸^,¹⁰^,¹¹

One recent systematic review found that LLIF was similar to posterior and anterior interbody approaches in success rates for addressing foraminal stenosis.³ There is considerably more debate regarding the ability of LLIF to treat central canal stenosis.¹²^,¹³^,¹⁴ Although some authors have suggested that indirect decompression can result in improved outcomes,⁵^,¹⁴ the limits of this technique are not yet well defined. The LLIF may not be an appropriate option to provide indirect decompression in patients with severe central stenosis, significant facet hypertrophy and ankylosis, bony stenosis (congenital stenosis), or calcified discs.

The ability to restore disc height and lordosis makes LLIF an attractive operation for patients presenting with ASD. In this population, LLIF has been associated with excellent (40–75%) correction of coronal deformity with more modest increases in lumbar lordosis.⁶^,¹⁵ The addition of an anterior column release (ACR) via transection of the anterior longitudinal ligament (ALL) and placement of hyperlordotic cages can restore lumbar lordosis via the lateral approach.¹⁶^,¹⁷^,¹⁸

38.3 Contraindications

Any aberrant neurovascular anatomy that limits safe access to the disc space is a contraindication to LLIF. Several authors have described the anatomy of the psoas muscle and lumbar plexus with respect to the lateral approach.¹⁹^,²⁰ The “safe zone” for approach is between the lumbar plexus (posterior) and abdominal vessels (anterior). At L4–L5 in particular, this safe zone narrows as the lumbar plexus moves more anteriorly and the vascular structures are more posterior on the disc space (Fig. 38.1). The access corridor at L4–L5 is generally narrower on the right hand side due to the vascular structures being more posterior.¹⁹ Despite these anatomic concerns, there is a robust body of literature supporting safety and efficacy of the LLIF using real-time, directional neural monitoring at the L4–L5 level.²¹^,²²^,²³

Fig. 38.1 Illustration of the safe zones relative to the neurovascular anatomy in the lumbar spine. Please note that the safe zone moves more anterior in the lower lumbar spine.

Another important consideration with establishing access to the disc space is pelvic morphology; a high pelvic brim may not allow for access to the L4–L5 disc space (Fig. 38.2). Other contraindications to LLIF include retroperitoneal scarring (due to prior retroperitoneal surgery, abdominal radiation, diverticulitis, etc.) and comorbidities that preclude fusion surgery (e.g., poor bone quality).

Fig. 38.2 Example of a patient with a high pelvic brim. Approaching the L4–L5 disc space would likely be not feasible via the lateral approach in this patient.

38.4 Preoperative Planning

Preoperative considerations for LLIF include: the side of approach, implant selection, implant sizing, and whether to add posterior instrumentation (Table 38.1). If L4–L5 is planned, the orientation of the L4–L5 disc space usually determines the side of approach. Obliquity of the L4–L5 disc space (e.g., in patients with degenerative scoliosis) can make the level accessible from one side only. In practice, we typically add posterior instrumentation for multilevel LLIF, patients with spondylolisthesis or spinal deformity, patients requiring anterior column (ALL) release, and patients at higher high risk for subsidence (e.g., poor bone quality). There is data to suggest that stand-alone LLIF may be sufficient in patients with low-grade degenerative spondylolisthesis.⁵ It is also important to closely assess the cross-sectional anatomy on magnetic resonance imaging (MRI) with particular attention being paid to the psoas muscle, the location of the vasculature, and the lumbar plexus. Louie et al recently described specific psoas morphology that may make lateral approaches more challenging in the lower lumbar spine.²⁴

Table 38.1 Ideal case, advantage, and radiologic goals of regular and hyperlordotic cages for an XLIF at L4–L5

XLIF L4–L5 Cages	XLIF L4–L5 Ideal case	XLIF L4–L5 Advantages	XLIF L4–L5 Radiologic goal degrees (max-min)
Regular	Degenerative disc disease or spondylolisthesis without sagittal imbalance	Excellent indirect decompression, large surface area for fusion	0–10 degrees²⁵
Hyperlordotic	Adult spinal deformity with PI-LL mismatch (use age-adjusted alignment), especially in patients with high pelvic incidence (majority of the lordosis should be at L4–S1); typically paired with ALL release	Sagittal correction without osteotomy; reduced EBL, fewer levels of fusion required²⁶	10–25 degrees²⁵
Abbreviations: ALL, anterior longitudinal ligament; EBL, estimated blood loss; PI-LL; pelvic incidence minus lumbar lordosis; XLIF, extreme lateral interbody fusion.

38.5 Patient Positioning

Patient positioning is a critical component of the LLIF procedure. Appropriate positioning requires a bendable, radiolucent surgical table. It is important to ensure that the fluoroscopy C-arm can rotate freely without being impeded by the base of the table.

Neuromonitoring leads (free-run electromyography [EMG]) are placed following induction of anesthesia while the patient is still supine. Because neuromonitoring is used during the approach, it is important that the anesthesiologist only use short-acting paralytics during induction.

Next, the patient is turned to lateral decubitus position with the iliac crest positioned at the level of the break in the table (Fig. 38.3). It is often helpful to slightly break the table to facilitate access to L4–L5 above the iliac crest and L1–L2 below the rib cage. It is important to ensure that all “down” surfaces (axilla, peroneal nerve, ulnar nerve) are appropriately padded. The arms are flexed approximately 90 degrees at the shoulder and elbow and supported on an arm board. A pillow or stack of blankets is typically placed between the arms.

Fig. 38.3 Appropriate positioning for a patient. Note that the Iliac crest is positioned just below the table break.

The hips and knees are then flexed to relax the psoas muscle and lumbar plexus. The patient is then secured to the bed with tape. We secure the torso with tape just below the iliac crest (over the greater trochanter) and just below the ribs. Tape is then run from the greater trochanter to the knees and brought around the table to the ankle and past the knee in a figure-of-eight fashion (Fig. 38.4). We routinely also secure the arms with a roll of tape.

Fig. 38.4 Tape is applied to secure the patient to the bed in the locations shown above. Please note that caution must be applied when taping the knee to ensure there is no undue pressure on the fibular head.

With the patient secured to the table, the bed is bent so that the head tilts down. This is done in conjunction with reverse Trendelenburg to keep the spine roughly parallel to the floor. The net effect of this maneuver is to tilt the pelvis away from the spine and allow for easier access to the disc spaces, particularly at L4–L5. An excessive break in the bed can cause neuropraxic injury to the lumbar plexus; therefore, we recommend bending the table just enough to tension the skin and allow for access to the disc space in question.

A twitch test is performed to ensure that muscle relaxants and paralytics are appropriately reversed before proceeding.

At this point, fluoroscopy is typically brought in to obtain an anteroposterior (AP) view of the spine. The C-arm base is brought in from the patients’ front (i.e., abdomen) side while the surgeon typically operates from the back (i.e., dorsal) side.

To ensure that the surgeon is oriented in an “up-down” position and working vertically across the disc space, the bed is adjusted to match the fluoroscopy machine, that is, the bed is rotated so that a perfect AP is obtained with the C-arm parallel to the floor (Fig. 38.5). Once the perfect AP is obtained, the C-arm is rotated 90 degrees to obtain a perfect lateral view of the disc in question. Again, the bed is adjusted so that a perfect lateral view is obtained with the C-arm perpendicular to the floor (Fig. 38.6).