Lateral Lumbar Interbody Fusion
Hamid Hassanzadeh
Varun Puvanesarajah
Frank M. Phillips
REBUTTAL ▪ The Case against MIS Lateral LIF
Susan Lammers
Douglas A. Hollern
Gregory D. Schroeder
Worawat Limthongkul
Kris E. Radcliff
Alexander R. Vaccaro
LATERAL LUMBAR INTERBODY FUSION INTRODUCTION
Lateral lumbar interbody fusion (LLIF) is a less invasive technique that allows for anterior interbody fusion through a direct lateral retroperitoneal transpsoas approach. The lateral approach aims to reduce surgical trauma to the paraspinal muscles and minimize direct manipulation of the neural and vascular elements. In addition, this approach capitalizes on the advantages of anterior interbody fusion including a large surface area for fusion, restoration of disk and foraminal height, and potential correction of both sagittal and coronal plane deformities. The procedure may be indicated whenever interbody fusion and anterior column support or reconstruction is required, proximal to L5-S1. Common indications include instability with spondylolisthesis, sagittal or coronal plane deformities, foraminal stenosis with disk space collapse, degenerative disk disease, adjacent segment pathologies, and pseudarthrosis. Stand-alone LLIF may be used in stable situations with a low risk of pseudarthrosis. In cases of instability or deformity and more complex reconstructions, LLIF is combined with posterior instrumentation. As the approach is through a retroperitoneal corridor, scarring of the retroperitoneal space or prior retroperitoneal surgery are relative contraindications. Due to the location of the iliac crest, L5-S1 pathology cannot generally be accessed by the LLIF technique.
TECHNIQUE
Anatomy
The LLIF technique involves access to the retroperitoneal space via the abdominal oblique muscles. Muscles that are dissected include, in order, the external oblique, internal oblique, transversus abdominis, quadratus lumborum, and psoas. While traversing the psoas muscle, nerves from the lumbar plexus are at risk.
The lumbar plexus is made of neural contributions from the ventral rami of L1-L4 and the subcostal nerve emanating from T12 (Fig. 26.1). Motor branches include the femoral and obturator nerves, while sensory branches include the genitofemoral, lateral femoral cutaneous, and iliohypogastric nerves. Anatomic variations in the lumbosacral plexus path is estimated to occur in 20% of people.1 Numerous anatomic studies have defined the path of the lumbar plexus in the psoas muscles with reference to lateral transpsoas access to the disk.2, 3, 4, 5 With the lateral aspect of the disk divided into quartiles from anterior to posterior, the “safe working zone” established by Uribe and colleagues is at the midpoint of the third quartile from the intervertebral disk spaces of L1-L2 to L3-L4. This safe zone moves anteriorly to the midpoint between the second and third quartiles when treating pathology at L4-L5.5 The genitofemoral nerve emerges from the psoas between L3 and L4 and is at risk when approaching these levels.
 Figure 26.1 Relevant neural anatomy. Exiting lumbar nerve roots coalesce to form the lumbar plexus. Note location of nerves within and around the psoas muscle. |
Aside from neural structures, other retroperitoneal structures, including the kidneys, ureters, and vascular structures, should be considered. However, major vascular structures are at less risk of injury when compared to anterior approaches.
Step-by-Step Technique
Patient Positioning
The patient is placed in the lateral decubitus position (Fig. 26.2A). The relevant anatomy and the presence of spinal deformity should be considered when deciding which side to approach from. In general, in cases of scoliotic deformity, approaching from the concavity will allow for easier access to the L4-L5 disk above the iliac crest.
The iliac crest is placed at the level of the table break. The bed is flexed in order to increase the working space between the inferior rib and the iliac crest (Fig. 26.2B). The legs are flexed at the knee and hips to decrease psoas tightness (Fig. 26.2A). Pressure points are padded and the patient is secured. The table is then adjusted to ensure that “true” anterior-posterior and lateral images can be achieved with C-arm fluoroscopy. A true anterior-posterior image is one where the spinous process is located at the midpoint between the pedicles. A lateral image should reveal no overlap of the vertebral endplates or pedicles. Fluoroscopy is used to identify the orientation of the disk space.
Surgical Approach
The LLIF approach was initially described with a posterior incision to provide finger access to the retroperitoneal space and a second incision directly over the lateral aspect of the disk of interest to access the disk and perform the arthrodesis. More recently, LLIF has also been performed with a single lateral incision.
After marking skin incisions and adequate draping and antiseptic preparation of the surgical site, a 2 cm posterior incision (Incision 1) is made at the lateral border of the paraspinal
musculature. Blunt dissection is taken through the transversalis until the retroperitoneal space is reached (Fig. 26.3A). At this point, further blunt dissection with the fingers is used to push the retroperitoneal contents anteriorly, allowing palpation of the psoas muscle, and providing a path for eventual dilatator and retractor positioning (Fig. 26.3B). After adequate blunt dissection, one may palpate the inner surface of the iliac crest, the inferior service of the 12th rib, and the transverse process posteriorly, as well. The finger is then advanced toward the primary incision overlying the intervertebral disk. The primary incision is then made ( Incision 2), running parallel to fibers of the external oblique and extending into the subcutaneous fat. The abdominal wall musculature is then gently spread.
musculature. Blunt dissection is taken through the transversalis until the retroperitoneal space is reached (Fig. 26.3A). At this point, further blunt dissection with the fingers is used to push the retroperitoneal contents anteriorly, allowing palpation of the psoas muscle, and providing a path for eventual dilatator and retractor positioning (Fig. 26.3B). After adequate blunt dissection, one may palpate the inner surface of the iliac crest, the inferior service of the 12th rib, and the transverse process posteriorly, as well. The finger is then advanced toward the primary incision overlying the intervertebral disk. The primary incision is then made ( Incision 2), running parallel to fibers of the external oblique and extending into the subcutaneous fat. The abdominal wall musculature is then gently spread.
 Figure 26.2 Patient positioning. (A) Left lateral decubitus position, with knees and hips flexed. (B) Iliac crest should be placed at the level of the table discontinuity. Table flexion allows increased working space between the inferior rib and the iliac crest. |
The first dilator is passed through the lateral incision. The surgeon’s finger should protect the dilator from anterior excursion that could penetrate the peritoneal cavity by guiding the dilator through its retroperitoneal passage (Fig. 26.3C). The dilator must be placed gently
on the psoas without incursion into the muscle. Lateral C-arm images are utilized to check positioning of the dilator in line with previously described “safe zones.” After ensuring correct positioning, the dilator is stimulated for electromyography (EMG) and rotated as it passes through the psoas muscle down to the level of the disk (Fig. 26.4). EMG activity indicating close proximity of the lumbar plexus mandates dilator repositioning, generally in an anterior direction.
on the psoas without incursion into the muscle. Lateral C-arm images are utilized to check positioning of the dilator in line with previously described “safe zones.” After ensuring correct positioning, the dilator is stimulated for electromyography (EMG) and rotated as it passes through the psoas muscle down to the level of the disk (Fig. 26.4). EMG activity indicating close proximity of the lumbar plexus mandates dilator repositioning, generally in an anterior direction.
 Figure 26.3 Access to the retroperitoneal space. (A) Initial entry through incision at the anterolateral aspect of the paraspinal musculature. (B) Blunt dissection with the fingers is used to push retroperitoneal contents anteriorly. (C) The finger is used to guide the dilator passed through the primary incision (The finger is used to guide the dilator passed through the primary surgical incision). |
 Figure 26.4 Dilator stimulation and final dilator docking at the disk space. |
Once the dilator is safely docked on the lateral disk, a guide wire is passed through the first dilator and into the disk space. With anterior-posterior C-arm images, guide wire placement is confirmed. Sequentially increasing diameter dilators are then introduced, each with concomitant dynamic EMG stimulation. Retractor blades are then inserted over the final dilator and locked into place. The surgical field should be explored with an EMG probe to ensure there are no nerves within the field. After inspecting the retracted field, an annulotomy is performed. The diskectomy is performed to the contralateral annulus without violation of the posterior and anterior annulus. Release of the contralateral annulus will facilitate mobilization of the level. Curettes, pituitary rongeurs, and broaches are used for the diskectomy and endplate preparation (Fig. 26.5). Once complete, distraction and sizing of the interbody is done. Serial trial spacers are used to size the interspace. The chosen interbody cage is then placed under fluoroscopy, usually packed with bone graft and/or biologics.
After irrigation and retractor removal, the wound is closed. The transversalis fascia is closed with absorbable sutures, followed by subcuticular skin closure.
Although this description of the technique focuses primarily on the lateral approach to interbody placement, many patients may require additional placement of posterior instrumentation for further stabilization.6
Complications
In general, medical complications occur in 1.9%7 to 3.7%8 of all patients undergoing the LLIF procedure. However, neurologic complications are of greatest interest.9 Reported complications include lower limb weakness and sensory deficits or paresthesias. A prospective study of 600 patients treated specifically with extreme lateral interbody fusions (XLIF) and real-time neuromonitoring at 741 levels observed a 6.2% perioperative complication rate. Of these patients, 4 (0.7%) had transient postoperative neurologic deficits.8 A retrospective review of 919 LLIF procedures by Lykissas et al. found persistent surgery-related sensory deficits in 9.3% of cases and motor deficits in 3.2% of cases, when excluding patients with preexisting neurologic deficit. Of the 87 patients with a minimum follow-up of 18 months, persistent
sensory and motor deficits were observed in 9.6% and 2.3% of patients, respectively.10 Other rare complications that have been noted include abdominal wall paresis,11 rhabdomyolysis and renal failure,12 and cage subsidence.13
sensory and motor deficits were observed in 9.6% and 2.3% of patients, respectively.10 Other rare complications that have been noted include abdominal wall paresis,11 rhabdomyolysis and renal failure,12 and cage subsidence.13
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