Introduction

Interbody lumbar fusion techniques have become increasingly popular because of improved rates of fusion, restoration of disc and foraminal height, and promotion of lordosis.¹ Accessing the anterior column of the lumbar spine lowers the incidence of pseudoarthrosis and recreates the patient’s normal sagittal alignment.² Late results of alleviating these effects through posterior fixation techniques alone show a significant loss of disc height at the injured segment and kyphotic deformation,³ necessitating access to the anterior column of the spine for interbody fusion. Conventional methods for accessing the anterior spine use an anterior retroperitoneal approach known as an anterior lumbar interbody fusion (ALIF), whereby a surgeon must mobilize the great vessels, sympathetic plexus, and ureter. This approach is associated with considerable surgical trauma, and higher rates of morbidity. As a result, most of these techniques typically require the presence of an experienced general or vascular surgeon, due to the risk of serious complications.²

Gaining popularity are techniques that access the anterior lumbar spine from a lateral retroperitoneal approach with the patient positioned in a lateral decubitus position. These procedures allow access to the anterior spine with little risk of injuring the peritoneum or great vessels, reducing the surgical risks compared to a standard ALIF operation. Since 1973, similar retroperitoneal approaches were documented to access the lumbar spine for performing lumbar sympathectomies and, starting in 1997 and 1998, Rosenthal et al. and McAfee et al., respectively, reported on minimally invasive anterior retroperitoneal approaches to the spine for anterior lumbar fusion. Early results show these alternative lateral approaches to the lumbar spine to be safe and effective for anterior fusion of the first through the fifth lumbar vertebrae.²

The guided lumbar interbody fusion (GLIF) technique is a lateral retroperitoneal approach whereby the lateral spine is accessed through a curvilinear portal with the patient in the prone position. Accessing the lateral spine while maintaining the patient in a prone position offers many advantages over similar lateral retroperitoneal approaches and conventional ALIF techniques. First and foremost, this procedure allows the addition of posterior fixation without having either to break the sterile field to rotate the patient mid-surgery or to stage a series of surgeries. This reduces the surgical time required for a full circumferential fusion procedure (otherwise known as a 360), which directly relates to decreased anesthesia time and costs for the patient, surgeon, and hospital.

Indications/Contraindications

Surgical indications for spinal fusion include discogenic pain, segmental spinal instability, progressive degenerative scoliosis, symptomatic spondylolisthesis, postsurgical pseudarthrosis, discitis, stenosis, degenerative disc disease, and lumbar vertebral fractures that may be alleviated with a lateral transpsoas approach.

Contraindications include systemic infection, osteoporosis, significant comorbidities, degenerative spondylolisthesis grade 3 or higher, and bilateral retroperitoneal scarring.

Additionally, the GLIF technique should be considered for revision surgery on patients with significant scar tissue from previous anterior or posterior approaches to the spine.

Description of the Device

At the center of the GLIF technique is the ARC Portal System, a curvilinear lighted retractor system with a hinged top (Figure 68-1). This instrument is delivered over sequential dilators to the disc space, and the hinged top can be opened to gain direct visualization of key surgical landmarks during disc preparation. The device has proximal and distal stabilization capabilities to prevent portal migration during the procedure. In addition to the ARC Portal System, the GLIF technique utilizes specialized instrumentation to efficiently prepare the disc space for implant delivery.

FIGURE 68-1 The retracted ARC Portal System against a representative lumbar spine.

Background of Scientific Testing / Clinical Outcomes

Bergey and Regan report, in a study conducted on 28 patients between 1996 and 2003, that early results show the lateral endoscopic transpsoas approach to the lumbar spine to be a safe, minimally invasive method for anterior fusion of the first through the fifth lumbar vertebrae. Their study indicates a risk of groin/thigh paresthesias and/or pain, but they report that these symptoms have proven to be transient. Of the 28 cases, eight patients experienced the transient groin/thigh numbness and/or pain; six patients experienced a small peritoneal perforation due to blunt dissection, with no bowel injuries; and two patients were converted to a mini-open lateral approach. Their report concludes that “this approach can be successfully combined with percutaneous pedicle screw fixation to provide a minimally invasive approach for circumferential fusions.”⁴

More recently, an extreme lateral interbody fusion technique (XLIF) has been adopted, with positive results. Pimenta indicates, in a study conducted to evaluate the XLIF technique for fixating lumbar degenerative scoliosis, that the transpsoas lateral approach has lower morbidity, does not require the use of endoscopes, avoids risks associated with anterior approaches, and avoids the invasion of the posterior spinal canal. Analyzing a consecutive series of 80 patients, Pimenta found the transpsoas approach to be a safe, reproducible, minimally invasive technique able to reconstruct sagittal balance, correct degenerative scoliosis, avoid the potential risks to the anterior approach, and promote rapid recovery.⁵

Wright reports similar results in a study of his first 10 patients to undergo the XLIF technique at Washington University. He reports the ability to perform a full discectomy, restore disc and foraminal height, as well as to achieve indirect canal decompression from L1 to L5. There were no vascular, visceral, or neurological complications. Nine out of ten patients ambulated on the day of surgery and were discharged on postoperative day one. One-year radiographic follow-up showed evidence of fusion. Additionally, the study indicated minimal narcotic requirement. Complications included three of 10 patients having transient pain with hip flexion that resolved by 6 weeks. His paper compared patients over 300 lb to those less than 300 lb, and found the surgical corridor to remain essentially the same length with no difference in outcomes, OR times, or blood loss. Hence, among one of the advantages of this technique he cited was that it is particularly useful in obese patients in whom anterior or posterior approaches would be more difficult.⁶

Clinical Presentation and Evaluation

This technology is novel and is currently in the alpha phase of release. At the time this chapter was published, only a few devices had been implanted using this technique. There have been no surgical complications to date, and follow-up data are presently being collected for better clinical evaluation.

Operative Technique

Proper patient positioning and delivery of the initial dilator are integral to the success of a GLIF technique. To facilitate proper trajectory of the instrumentation, the Calibrated Introducer was developed to repeatedly and reliably deliver the instruments to the surgical site (Figure 68-2).

FIGURE 68-2 The Calibrated Introducer delivering the Initial Dilator.

The patient is positioned on the operating table in the prone position, and lateral fluoroscopy is used to locate the proper operative level. The Calibrated Introducer is placed along the midline of the patient’s back, directly above the operative level, and then secured with a Table Fixation Arm. The Calibrated Introducer is adjusted to locate the posterior one third of the operative disc space, which in turn identifies the axis of rotation for the curvilinear trajectory. Dilator 1 is attached to the Calibrated Introducer swing arm (centered on the identified axis of rotation) and rotated until the distal tip of Dilator 1 touches the patient’s skin. At this location, a 4 cm transverse incision is made through the patient’s skin and fascia. A finger is used to palpate through the subcutaneous tissue into the retroperitoneal space, and can be used to sweep the peritoneum anteriorly and identify either the psoas muscle or the anterior tops of the transverse processes.

Using the surgeon’s finger as a guide, Dilator 1 is advanced along the calibrated trajectory and delivered into the retroperitoneal space, through the psoas muscle, and up to the annular wall of the desired location. Throughout this step and the following sequential dilaution procedure, standard neuromonitoring technology can be utilized to ensure safe delivery of the dilators around the nervous structures. Proper dilator placement is confirmed with lateral fluoroscopy, then anterior-posterior fluoroscopy. A guidewire is delivered through the cannula of Dilator 1 into the vertebral disc and then Dilator 1 is impacted into the intervertebral disc space, approximately 3 to 4 cm or to the midline. At this point, fluoroscopy can be used to verify final placement of the initial dilator. The guidewire and Calibrated Introducer can then be removed. Dilator 1 implanted into the intervertebral disc space provides a fixed trajectory to the surgical site for the following access instrumentation.

Sequential dilation is performed using Dilator 2 and Dilator 3 to retract the soft tissue through the retroperitoneal space and psoas muscle in preparation for the delivery of the access portal. The ARC Portal is delivered over Dilator 3 and gently manipulated until the instrument is fully seated against the lateral wall of the anterior spinal column (Figure 68-3). Throughout the procedure, anterior-posterior fluoroscopy is used to confirm instrument placement and trajectory. Final placement of the device is maintained using a Table Fixation Arm. An Anterior Awl that retracts from the ARC Portal is deployed into the intervertebral disc space to establish distal fixation to the spine, and the dilators are removed.

FIGURE 68-3 The ARC Portal delivery over sequential dilators.

Related posts:

Embryology of the Spine Non-Invasive Strength Analysis of the Spine Using Clinical CT Scans Tumors of the Cervical Spine Rheumatoid Arthritis of the Cervical Spine The Role of Spinal Fusion and the Aging Spine: Stenosis without Deformity Interspinous Spacers for Minimally Invasive Treatment of Dynamic Spinal Stenosis and Low Back Pain

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