Chapter 36 Transaxial Anterior Lumbar Interbody Fusion Using The AxiaLIF System

Luiz M. Pimenta, MD, PhD, Carlos F. Arias, MD, Juliano Lhamby, MD, Leonardo Oliveira, BSc, Thomas Schaffa, MD, Etevaldo Coutinho, MD

The rate of minimally invasive spine surgery (MISS) has increased in recent years because of the development of technology and new approaches to the spine. Open lumbar surgery is disadvantageous because of the need of muscle and neural retraction, ligamentous and osseous dissection, disruption of the anulus, and vascular exposure [1]. For most MISS techniques, the approach is like those used in open approaches to the spine—that is, posterolateral and extraforaminal exposure of the disc space and incision or excision of the anulus [2–9].

When stabilization of the lumbosacral spine is indicated, however, a less invasive axial lumbosacral surgery offers significant advantages over MISS techniques [10–13]. This technique, transaxial anterior lumbar interbody fusion, uses a percutaneous, presacral approach. Use of the AxiaLIF System, manufactured by TranS1, Inc. (Wilmington, NC), is described in this chapter, first for stabilization at one level, and then for stabilization at two levels.*

Potential complications

The presacral access tract traverses posterior to the bowel and anterior to the sacrum. Possible risks of access include infection from bowel injury and bleeding from injury to the presacral artery. Fluoroscopic monitoring, rectal air insufflation, blunt access instruments, and dilation rather than sharp dissection into the sacral face mitigate these risks.

The sacral entry site at S1-S2 is a relatively bare area in the pelvis because the major neural and vascular structures are lateral to the midline at this point.

In the spine itself, there is a risk to spinal canal contents if the trajectory into the disc space is inappropriate or if rotational cutting tools used for discectomy are too large. As with all image-guided operations, careful attention to landmarks is imperative to minimize the risk of complications. The most important factor in reducing risk is expertise in image-guided surgery.

Presacral anatomy

Axial anterior spinal access is accomplished by dilating an osseous tract through the upper sacrum. The midline entry point in to the sacral promontory at approximately the S1-S2 interspace is relatively bare area compared with the more complex vascular and neural structures encountered over the lower lumbar spine (Fig. 36-1) [14,15]. At the sacral level, the iliac vessels and their accompanying sympathetic hypogastric nerves have diverged by several centimeters. The middle sacral artery follows a variable course over the sacrum but is usually small at the S1-S2 level. The rectum and sigmoid colon are easily mobilized in the presacral region. The presacral space is filled with areolar tissue and fat between the parietal peritoneum on the anterior sacrum and the visceral peritoneum on the rectum (see Fig. 36-1). The space is relatively easily traversed with a blunt obturator or needle.

Figure 36–1 Vascular anatomy of the sacral region. The aorta and vena cava are seen bifurcating at the L4-L5 level. The iliac vessels are several centimeters lateral to the midline. The arrow shows that the sacral entry point is placed in a safety zone.

AxiaLIF at one level

Procedure

Patient Positioning

In the AxiaLIF technique, multiplanar imaging with magnetic resonance (MRI) and/or computed tomography (CT) is essential to determine whether the patient is a proper surgical candidate. A standard bowel preparation is performed. The patient is placed on a fluoroscopically compatible surgical table in the prone position (Fig. 36-2). Bolsters are positioned under the hips and shoulders to raise the sacrum and establish proper lumbosacral posture. A catheter is inserted into the rectum to allow insufflation of air. The operative site is prepared with an adhesive barrier to exclude the perineum. Two C-arm fluoroscopic units are positioned to allow frontal and lateral (biplanar) fluoroscopic visualization of the lumbosacral region. The procedure is currently performed using general anesthesia.

Figure 36–2 The patient is placed on a fluoroscopically penetrable surgical table in the prone position, and bolsters are positioned under the hips and shoulders to raise the sacrum and establish proper lumbosacral posture.

Approach

The AxiaLIF technique provides percutaneous access to the lumbar spine through the anterior presacral space (Fig. 36-3A). The developed instruments facilitate a safe and reproducible entrance to the L5-S1 disc space (Fig. 36-3B).

Figure 36–3 A1) The paracoccygeal notch is palpable and serves as the window for entry into the presacral space. (A2) The incision is made at this point. A blunt guide pin is advanced to the arch of the caudal sacrum and then directed inferiorly under the arch. It is very important to use biplane fluoroscopy to ensure safe advancement in all steps. After traversing the pelvic fascial layer, the guide pin shaft is deflected downward, to direct the tip posteriorly against the anterior wall of the sacrum. Pin position against the sacrum is maintained by downward pressure on the guide pin shaft. The trajectory of the entry into the anterior lumbar spine is defined when the blunt pin reaches the S1-S2 interspace, with constant fluoroscopic monitoring in two planes. (A3) A sharp guide pin in then tapped into the sacrum, followed by a series of dilators to enlarge a tract into the sacrum. A cannula is then inserted over the largest dilator to provide a safe access for the remainder of the operation. (B) AxiaLIF instrumentation.

Radial Discectomy

Axial disc access is accomplished through the 9-mm sacral working cannula. Custom MISS instruments for discectomy, end plate preparation, tissue removal, and bone grafting are inserted through the working cannula (Fig. 36-4). The instruments are monitored with biplanar fluoroscopy. Axial disc space entry facilitates the use of expansible, radial instruments that are aligned in the plane of the disc space and end plates. Thus minimally invasive discectomy is potentially easier and more complete with axial disc space entry than with horizontally oriented, posterolateral approaches.

Figure 36–4 The discectomy, end plate preparation, and bone grafting are performed before implant insertion. Expandable Nitinol discectomy/cutters are inserted to remove the intervertebral disc, preparing the fusion bed.

Treatment Alternatives

The potential applications for minimally invasive axial anulus- sparing access to the spine are numerous. They include percutaneous axial fusion with or without posterior instrumentation and multilevel fusion through a single incision, as well as insertion of motion-preserving implants.

Percutaneous Axial Lumbar Interbody Fusion

One option to fusion of the L5-S1 is the use of a single-piece distraction rod as a long-term fusion implant in conjunction with bone graft and/or bone-morphogenetic substances. In addition, although the rod depicted in most of the figures in this chapter is constructed of metal, other synthetic or biologic materials could be used.

The anterior interbody construct we describe, in conjunction with advancements in percutaneous posterior instrumentations techniques, allows a muscle-sparing circumferential fusion construct at L5-S (Fig. 36-6).

Figure 36–6 The rod can be constructed in two parts to allow its removal without reducing the degree of distraction or as a single part for permanent implantation.

Case Series [16,17]

The authors conducted a case series involving 19 patients with a median age of 51 years. Subjects were evaluated preoperatively, postoperatively, and at discharge, 1 and 6 weeks, and 3, 6, 12, 24, and 30 months.

Assessment consisted of the following:

Measurement of disc height and fusion through radiography and CT evaluation by an independent radiologist

Pain assessment by means of a visual analog scale (VAS), Oswestry Disability Questionnaire, and the SF-36 Health Survey

Fixation of the lumbosacral junction was performed through a 14-mm access cannula via an axial presacral approach. Treatment was facilitated by insertion of an axial interbody fusion construct coupled with osteogenic material and posterior minimal invasive pedicle screw instrumentation. The 360-degree minimally invasive fusion approach was accomplished through three small (2-in.) incisions. Mean surgical time was 122 minutes. In all cases measured blood loss was less than 60 mL.

Postoperative pain was minimal. There were no cases of bowel, vascular, or nerve damage. Improvements were observed

CASE STUDY 36.1

A 45-year-old woman had discogenic-type low back pain that intensified with standing and flexion. In addition, she had neurogenic claudication symptoms. Preoperative MRI and radiography showed narrowing and desiccation of the L5-S1 disc space with a spondylolisthesis grade II (Fig. 36-7). She underwent the AxiaLIF procedure at the L5-S1 level (Fig. 36-8). Radiographs obtained 12 months after surgery showed osseous bridging of L5-S1 and reduction of the spondylolisthesis (Fig. 36-9). CT scans demonstrated no evidence of radiolucency on the pedicle screws and the distraction rod (Fig. 36-10) and, along with a three-dimensional reconstruction, also showed solid osseous fusion of the L5-S1 interspace (Fig. 36-11).

Figure 36–7 Case Study 36.1: Preoperative sagittal MRI (B) and lateral radiograph (A) shows narrowing and desiccation of the L5-S1 disc space with a spondylolisthesis grade II.

Figure 36–8 Case Study 36.1: AxiaLIF procedure step by step.

Figure 36–9 Case Study 36.1: Lateral (A) and anteroposterior (B) radiographs obtained 12 months after surgery show osseous bridging of the L5-S1 interspace and reduction of the spondylolisthesis.

Figure 36–10 Case Study 36.1: (A) Axial computed tomography CT) scan obtained 12 months after surgery shows no evidence of radiolucency on the pedicle screws and the distraction rod. Sagittal (B) and coronal (C) CT scans demonstrates osseous fusion of the L5-S1 interspace.

Figure 36–11 Case Study 36.1: One year postoperatively, three-dimensional reconstruction shows solid fusion.

in VAS, Oswestry, and SF-36 values measured again at 2 years after surgery. The mean VAS score decreased from a preoperative value of 8.3 to 3.4. The mean Oswestry Disability Index improved from 43.1 to 21.0. Radiographic analysis concluded that there was no evidence of implant back-out, damage, bone resorption, fractures, or sacral abnormalities.

Two measurements of the disc height were made preoperatively and postoperatively, one in the midline and the other in the posterior border of the disc space. Preoperatively, mean midline disc height was 6.06 (range 2-11), and mean posterior border disc height was 4.8 (range 2-9). Postoperatively, the mean midline disc height was 7.5 [range 5–11], and mean posterior border disc height was 6.06 (range 3-9). CT scans demonstrated of fusion rate to be 89.5% at 12-month follow-up, and 94.7% at 30 months after surgery (18 of 19 patients).

AxiaLIF at two levels

The AxiaLIF (Axial Lumbar Interbody Fusion) 2L System (TranS1, Inc.) includes surgical instruments for “creating a safe and reproducible presacral access route to the L4-S1 vertebral bodies [18].” The technique features instrumentation to enable standard of care fusion principles, distraction, and stabilization of the anterior lumbar column while mitigating the soft tissue trauma associated with traditional lumbar fusion through open surgical incisions. With the use of this system, the lumbar spine is accessed through an axial channel in the sacrum. This approach spares the supporting soft tissue including muscles and ligaments which reduces pain in recovery and the chances of soft tissue associated complications.