Transaxial Anterior Lumbar Interbody Fusion Using the AxiaLIF System

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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.

Advantages

Advantages of the AxiaLIF 2L System are as follows:

Safe, reproducible, presacral approach

Percutaneous access

Spares soft tissues

No anular disruption

Patients released from hospital in as little as 1 day

Restoration of disc height to approximate adjacent healthy spinal segments

Immediate rigid segmental fixation and stability of L4-S1

Indications

The AxiaLIF 2L System is intended to provide anterior stabilization of the L4-S1 spinal segments as an adjunct to spinal fusion. It is indicated for use in patients requiring fusion to treat pseudoarthrosis, unsuccessful previous fusion, spinal stenosis, spondylolisthesis (grade I or II), or degenerative disc disease, defined as back pain of discogenic origin with degeneration of the disc confirmed by history and radiographic studies. This system is also intended for minimally invasive access to the anterior portion of the lower spine for assistance in the treatment of degeneration of the lumbar disc, performing lumbar discectomy or in the performance of L4-S1 interbody fusion. Its usage is limited to anterior supplemental fixation of the lumbar spine at L4-S1 in conjunction with legally marketed facet and pedicle screw systems.

Warnings

The risks to the patients are similar to those for patients undergoing any spine stabilization surgery. The most frequently stated risks are bleeding (including occult during and after surgery), neurologic damage, damage to soft tissue, spinal cord impingement or damage, infection, loss of bowel or bladder function, loss of erectile or ejaculatory function, meningitis, and pain.

The safety and effectiveness of this device have not been evaluated in patients with spondylolysis. Pedicle screw systems, not facet screws, should be considered when there is degenerative disease of the facets with instability.

The risks associated with the implant itself include breakage of the implant, loosening or expulsion of the implant with possible delayed nerve root impingement or damage, fracture of osseous structures, and bursitis. The presence of the device may also cause pain, discomfort, or abnormal sensations.

The risks associated with harvesting of autologous grafts are pain at the donor site, infection, herniation, and fracture. There may also be non-union or delayed union of fusion with the autologous graft.

Precautions

Preoperative

Portions of this system are supplied nonsterile and need to be cleaned and sterilized according to the instructions in the product insert [18].

Intraoperative

All steps of the procedure should be followed as per the procedure section below. All steps in this technique require the use of active or real-time fluoroscopy. Refer to the procedure section for proper implant sizing.

Postoperative

Risk of occult bleeding exists during and after the procedure. As with all surgical procedures, careful patient monitoring is required to minimize this risk. Following the procedure, the patient should be monitored until released for any effects of the procedure. The patient should adhere to postoperative instructions as provided by the physician.

Preoperative Planning

Radiographic images including a full sacral view are used to determine whether the anatomy is suitable for the AxiaLIF 2L procedure. The standard field of view for lumbar MRI and CT is expanded to include the coccyx, to provide for trajectory and anatomical preoperative planning.

Trajectory is extremely important with the AxiaLIF 2L procedure. Templates are available and should be used to help the surgeon determine whether the patient is a candidate for this procedure, as follows:

Match the scale of the MRI or CT image with the magnification scale on the template. The template’s magnification scale is relative to the actual size of the implants but does not necessarily correlate with the scale size printed on the MRI or CT image. If a magnification scale does not exactly match the scale on the image, err on the side of the larger template magnification scale. Adjust the chosen template so that the implants are positioned within the vertebral bodies and do not breach the cortex of the vertebral body. Examine the location of the lines of the guide pin introducer relative to the coccyx. The patient is probably a candidate for this procedure if the lines are reasonably close to the tip of the coccyx.

Additionally, a true lateral radiograph should be taken of the lumbosacral region, including the coccyx, with the patient in a prone position and the hips in flexion. It should be used as follows to further determine whether the AxiaLIF procedure is appropriate for the individual patient: Draw a line on the radiograph from the anterior aspect of the superior L4 end plate parallel to the anterior cortex of the L5 vertebral body toward and beyond the coccyx. Draw another line coincident with the posterior cortex of the L5 vertebral body toward and beyond the coccyx. The patient is likely a candidate for the procedure if any portion of the tip of the coccyx lies between the two lines.

Patient Preparation

The patient’s written informed consent is obtained.

Standard bowel preparation is performed the evening before.

Standard spine surgery preparation is made.

The patient is placed in the prone position with pelvic elevation.

The sacrococcygeal region is surgically prepared.

The operative area is isolated with an occlusive dressing.

Operating Room Setup

Biplanar fluoroscopy is an advantage.

The C-arm fluoroscope should be positioned as follows: anteroposterior (AP) and lateral fluoroscopic images are oriented to ensure adequate visualization and to determine left versus right correspondence.

Procedure

The AxiaLIF 2L procedure is performed as follows; the instruments with capitalized names are proprietary instruments available from Trans1, Inc.

Step 1: Access and Trajectory

1. Palpate the coccyx and sacrococcygeal ligament arch. Make a 15- to 20-mm incision to the left or right of the coccyx through the skin and superficial fascia 3 to 4 cm caudal to the paracoccygeal notch (Fig. 36-12).

2. Use the Blunt Guide Pin Introducer to penetrate the fascia immediately below the ligaments (Fig. 36-13). Advance the Blunt Guide Pin Introducer cephalad along the midline, keeping the tip engaged on the anterior cortex of the sacrum to approximately the S1-S2 junction (Fig. 36-14).

Figure 36–12 Incision point.

Figure 36–13 Maneuver to access the sacral space.

Figure 36–14 Access direction.

This maneuver is accomplished with “fingertip” control on the handle of the Blunt Guide Pin Introducer and should be completed with use of fluoroscopic guidance in both AP and lateral planes.

3. A template is available to aid in choosing the appropriate trajectory as described above in the preoperative planning section.

4. Orient the template so that neither implant will breach the cortex of the vertebral body, the Ø13MD Threaded Length of the Distal Rod matches the L5 body as closely as possible, and the circles on the template are just below the disc space.

5. Adjust the Guide Pin Introducer to match the trajectory suggested by the template.

6. Once the trajectory is established, exchange the Blunt Stylet for the Beveled Guide Pin. Attach the Beveled Guide Pin to the Guide Pin Handle with the bevel tip of the pin corresponding to the thumbscrew on the handle (Fig. 36-15).

7. While maintaining trajectory, gently tap on the Guide Pin Handle with the Slap Hammer to dock the Beveled Guide Pin into the sacrum.

8. Confirm the trajectory with AP and lateral fluoroscopic imaging, and gently tap the Beveled Guide Pin through the sacrum and into the L5-S1 disc space (Figs. 36-16 and 36-17).

9. Confirm, with the template, that the trajectory of the Beveled Guide Pin will allow for proper placement of both implants.

Figure 36–15 Blunt Guide Pin Introducer.

Figure 36–16 Positioning the Guide Pin into the S1 using the Guide Pin handle.

Figure 36–17 Beveled Guide Pin inserted at L5-S1.

NOTE: If resulting placement of the Beveled Guide Pin is unsatisfactory, the Beveled Guide Pin should be removed and re-inserted until the proper trajectory is achieved.

10. Remove the Guide Pin Handle, and attach the Guide Pin Extension.

11. Carefully pull the Guide Pin Introducer back over the Extended Guide Pin, using the extra length to ensure that the Beveled Guide Pin remains in position during removal of the Introducer (Fig. 36-18).

Figure 36–18 Guide Pin Handle removal.

Step 2: Discectomy at L5-S1

A series of instruments is used to sequentially dilate the soft tissue and sacral corticocancellous bone to create the working channel, as follows:

1. Slide the 6-mm Dilator over the Beveled Guide Pin to the S1-S2 junction. Use the Slap Hammer to advance the Dilator into the sacrum approximately halfway to the disc space (Fig. 36-19).

2. Remove the 6-mm Dilator, leaving the Beveled Guide Pin in place, and repeat with the 8-mm Dilator.

3. Remove the 8-mm Dilator and repeat with the 10-mm Dilator Assembly. The 10-mm Dilator is assembled with 10-mm Dilator Sheath that slides over the 10-mm Dilator body and engages with a pin-slot configuration (Fig. 36-20).

4. Advance the 10-mm Dilator far enough into the sacrum to ensure that the outer diameter of the sheath is placed completely within the sacral cortex (Fig. 36-21).

5. Once the Dilator with Sheath is anchored in the sacrum, remove the Dilator body from the Sheath by disengaging the pin-slot configuration and carefully withdrawing the Dilator body (Fig. 36-22).

6. Insert the Cannulated 9-mm Twist Drill over the Beveled Guide Pin. Debulk the channel to the L5-S1 disc space by rotating the drill with a clockwise motion (Fig. 36-23)

7. Remove the Cannulated 9-mm Twist Drill. When extracting the drill, continue rotating in a clockwise motion. This technique helps hold pieces of bone within the flutes of the drill. These pieces of bone are placed aside in saline to be used later in the procedure as supplemental bone graft material (Fig. 36-24).

8. Reinsert the 10-mm Dilator over the Beveled Guide Pin and reengage with the 10-mm Dilator Sheath.

9. Remove the 10-mm Dilator with Sheath Assembly, leaving the Beveled Guide Pin in place.

10. The 12-mm Dilator is assembled with the 12-mm Dilator Sheath, which slides over the Dilator body and engages with a pin-slot configuration (Fig. 36-25). Insert the 12-mm Dilator with Sheath Assembly over the Beveled Guide Pin.

11. Use the Slap Hammer to dock the Sheath in the sacrum.

12. Advance the 12-mm Dilator far enough into the sacrum to ensure the outer diameter of the sheath is placed completely within the sacral cortex.

13. Remove the 12-mm Dilator from the 12-mm Dilator Sheath. The Dilator Sheath should remain anchored to the sacrum to serve as a protected working channel for other instrumentation.

14. Once the 12-mm Dilator Sheath is securely anchored to the sacrum, the Beveled Guide Pin can be removed.

15. Insert the 10.5-mm Drill through the Dilator Sheath, and rotate the handle clockwise, drilling through the sacrum and into the disc space. Use fluoroscopy to verify how far to drill into the sacrum and disc (Fig. 36-26).

16. When extracting the Drill, continue twisting in a clockwise motion. This technique helps hold pieces of bone in the flutes of the drill. These pieces of bone are placed aside in saline to be used later in the procedure as supplemental bone graft material (Fig. 36-27).

Figure 36–19 Slap hammer positioning the Dilator into the sacrum.

Figure 36–20 Pin slot configuration of the 10-mm Dilator.

Figure 36–21 10-mm Dilator placed into the sacrum cortex.

Figure 36–22 Dilator removal.

Figure 36–23 Rotation of the cannulated 9-mm Twist Drill debulking a channel to the disc space.

Figure 36–24 9-mm Drill removal.

Figure 36–25 12-mm Dilator engaged at the pin slot configuration.

Figure 36–26 Clockwise rotation of the 10.5-mm drill.

Figure 36–27 10.5-mm Drill removal.

A series of Nitinol Disc Cutters, varying in length and cutting action, is used to prepare the disc space. Each of the four cutters is designed to debulk the nucleus pulposus and to lightly abrade the end plates circumferentially up to a 3-cm diameter footprint while creating a bleeding bed for fusion. The Radial Cutters are designed to debulk the nucleus pulposus and to the scrape the superior end plate. The Radial Downcutters are specifically designed to abrade the inferior end plate. They are used as follows:

17. Retract the flexible Nitinol blade of the Small Radial Cutter into the cutter sleeve. The handle and blade orientation correspond. Insert the cutter through the 12-mm Dilator Sheath into the disc space.

18. Once inside the disc space, deploy the blade anteriorly and begin a series of cutting motions by rotating the handle in 90-degree turns to cut and remove tissue (Figs. 36-28 and 36-29). The double-edged blade allows cutting in both directions.

19. Repeat as necessary with subsequent cutters.

Figure 36–28 Flexible Nitinol blade removing the disc.

Figure 36–29 Rotation of the handle to cut and remove the disc.

NOTE: The blade must be retracted before being removed from the disc space.

Tissue Extractors are used to remove disc material loosened by the cutters. Tissue Extractors may be used after each cutter or after cutting is mostly complete, as follows:

20. Retract the Tissue Extractor head into the sleeve before inserting it through the 12-mm Dilator Sheath.

21. Advance the Tissue Extractor to the L5 end plate, and then retract the sheath.

22. Rotate the Extractor no more than six full revolutions counterclockwise, and remove it by pulling the entire Extractor unsheathed (Fig. 36-30).

23. Discard the Extractor, and repeat as necessary.

Figure 36–30 Rotation of the Tissue Extractors to remove the disc.

NOTE: Flush and aspirate as needed with saline, adding antibiotic according to standard procedure.

Step 3: Bone Grafting at L5-S1

Prepare the bone graft material by utilizing all of the autologous material harvested during the drilling. Supplement the bone graft with additional osteogenic material as needed. The procedure is as follows:

1. Load bone graft material into the distal end of the Bone Graft Inserter (Fig. 36-31).

2. Use the Bone Graft Inserter to place bone graft material into the disc space.

3. Push the material into the disc space, and pack it, by pushing the Inserter Rod through the cannula (Figs 36-32 and 36-33). The beveled tip should be rotated to deliver material into the disc space in quadrants. In patients with previous discectomy, aim the bevel anteriorly and laterally. Aim the bevel posteriorly only with caution.

Figure 36–31 Loading the Bone Graft Inserter with bone graft material.

Figure 36–32 Impaction of the bone graft material.

Figure 36–33 Bone graft material at the L5-S1 disc space.

Step 4: Advance Access to L4-L5

1. Re-insert the 12-mm Dilator and engage the Dilator Sheath using the pin-slot configuration.

2. Advance the 12-mm Dilator and Sheath with the Slap Hammer up to the L5 vertebral body; engage the tip of the sheath with the L5 vertebra (Fig. 36-34).

3. Once the Dilator Sheath is engaged in the L5 vertebra, remove the Dilator body from the Sheath by disengaging the pin-slot configuration and carefully withdrawing the Dilator body (Fig. 36-35).

4. Insert the 2-Level 9.0-mm Drill into the 12-mm Dilator Sheath, and rotate the handle clockwise to drill through the L5 vertebral body and into L4-L5 disc space. Fluoroscopy should be used to ensure that drilling does not extend beyond the L4-L5 disc space (Fig. 36-36).

5. When extracting the Drill, continue twisting in a clockwise motion. This helps hold pieces of bone in the flutes of the drill. These pieces of bone are placed aside in saline to be used later in the procedure as supplemental bone graft material.

6. Perform the second radial discectomy in the same manner as the first, using the same series of Nitinol Disc Cutters.

7. Retract the flexible Nitinol blade of the Small Radial Cutter into the cutter sleeve. The handle and blade orientation correspond.

8. Insert the Cutter through the Dilator Sheath into the disc space.

9. Once the cutter and sheath are inside the disc space, deploy the blade anteriorly, and begin a series of cutting motions by rotating the handle in 90-degree increments to cut and remove tissue (Figs. 36-37 and 36-38). The double-edged blade allows cutting in both directions.

10. Repeat as necessary with subsequent cutters.

Figure 36–34 Slap hammer positioning the Dilator into the L5 vertebral body.

Figure 36–35 Removal of the Dilator.

Figure 36–36 Two-level drill accessing the L4-L5 disc space.

Figure 36–37 Rotation of the handle to cut and remove the disc.

Figure 36–38 Flexible Nitinol blade removing the disc.

NOTE: The blade must be retracted before being removed from the disc space.

Tissue Extractors are used to remove disc material loosened by the cutting devices. Tissue Extractors may be used after each cutter or after cutting is mostly complete (Fig. 36-39), as follows:

11. Retract the Tissue Extractor head into its sleeve before inserting it through the Dilator Sheath.

12. Advance the Tissue Extractor to the L5 end plate, and then retract the sheath.

13. Rotate the Extractor no more than six full revolutions counterclockwise, and remove by pulling the entire Extractor unsheathed.

14. Discard the Extractor, and repeat as necessary.

Figure 36–39 Rotation of the Tissue Extractors to remove the disc.

NOTE: Flush and aspirate as needed with saline, adding an antibiotic according to standard procedure.

Step 6: Bone Grafting at L4-L5

1. Prepare the bone graft material by utilizing all of the autologous material harvested during the drilling.

2. Supplement the bone graft with additional osteogenic material, as needed.

3. Load bone graft material into the distal end of the Bone Graft Inserter (Fig. 36-40).

4. Use the Bone Graft Inserter to place bone graft material into the disc space.

5. Push the material into the disc space, and pack it by pushing the Inserter Rod through the cannula (Figs. 36-41 and 36-42). The beveled tip should be rotated to deliver material into the disc space in quadrants. In patients with previous discectomy, aim the bevel anteriorly and laterally. Aim the bevel posteriorly only with caution.

Figure 36–40 Loading the Bone Graft Inserter with bone graft material.

Figure 36–41 Impaction of the bone graft material.

Figure 36–42 Bone graft material at the L4-L5 disc space.

Step 7: Implant Selection and Delivery

1. Insert the 2-Level 7.5-mm Drill into the 12-mm Dilator Sheath, and rotate the handle clockwise to drill to the depth suggested by the template into the L4 vertebral body. Use fluoroscopy to verify how far to advance the drill (Fig. 36-43).

2. When extracting the Drill, twist in a counterclockwise direction in order to leave behind the bone packed into the disc space in the previous step.

Figure 36–43 Two-level drill accessing the L4 vertebrae.

L4-L5 implant selection

The .092-inch Guide Pin is used under fluoroscopy to determine the appropriate implant size, as follows:

1. Insert the .092-inch Guide Pin until the tip is adjacent to the cephalad L4 end plate.

2. Using a small clip or clamp, mark the location on the Guide Pin where it comes out of the dilator sheath (Fig. 36-44).

3. Slowly withdraw the Guide Pin under fluoroscopy until the Guide Pin tip (arrow) is located just inferior to the caudal L5 end plate.

4. With the tip of the Guide Pin just below the L5 end plate, use a small clip or clamp to mark the location on the pin where it comes out of the dilator sheath.

5. There are gradation marks every 10 mm on the Guide Pin to assist in measuring. Count the number of gradation marks located between the two clamps. Round to the nearest proximal threaded segment of the distal implant length (25 mm or 30 mm).

6. Remove both clips from the .092-inch Guide Pin.

7. Reinsert the .092-inch Guide Pin to the end of the bore in the L4 vertebral body. Mark the .092-inch Guide Pin with a clip or clamp at the end of the 12-mm Dilator Sheath.

8. Slowly withdraw the .092-inch Guide Pin under fluoroscopic guidance until the pin is located just inferior to the caudal L5 end plate. The distance between the clips corresponds to the overall length of the desired implant (Fig. 36-45). If the distance between the clips does not exactly match the published length of an implant, round down to the closest length.

Figure 36–44 Use of the .092-inch Guide Pin to locate the cephalad L4 end plate and mark it with a clamp.

Figure 36–45 Use of the .092-inch Guide Pin to locate the caudal L5 end plate and mark it with a clamp.

The desired distraction should be selected on the basis of the patient’s anatomy. The distal rod will engage in the L4 vertebral body and then span the L4-L5 disc space and the L5 vertebral body. The distal rod may extend into the L5-S1 disc space or may be recessed slightly into the L5 vertebral body.

9. After measuring, return the .092-inch Guide Pin to the end of the bore in the L4 vertebral body. Evaluate the sacral face in the lateral view to choose which Exchange System (30-degree or 45-degree) better matches the contact angle.

10. Remove Dilator Sheath using the 12-mm Dilator, being careful to leave the Guide Pin in place.

11. Place the selected Exchange Bushing over the 092-inch Guide Pin, advancing it with the long mark facing dorsally until it contacts the sacral face. Verify correct placement.

12. Simultaneously rotate the Bushing 180 degrees and continue advancing the Bushing until the angled surface of the bushing meets the sacral face.

13. Advance the corresponding Exchange Cannula over the Bushing until it contacts the sacral face. Verify correct placement.

14. Simultaneously rotate the Exchange Cannula 180 degrees while continuing to advance the Cannula until the angled surface of the cannula meets the sacral face (Fig. 36-46).

Figure 36–46 Exchange Cannula in contact with the sacral face.

A Fixation Wire is then used to anchor the Exchange Cannula to the sacrum, as follows:

15. Insert the Fixation Wire through the small lumen at the proximal end of the T-shaped handle on the Exchange Cannula.

16. Advance the Fixation Wire 1-2 cm into the sacrum using a wire driver. When it is correctly placed, bend the wire out of the way.

17. Remove the Bushing, leaving the Guide Wire and Exchange Cannula in place. This step should be completed under fluoroscopic guidance to ensure that the Exchange Cannula and Guide Pin remain in position.

L4-L5 implant delivery

1. Place the selected implant over the .092-inch Guide Pin.

2. Advance implant and driver together over the Guide Pin and through the Exchange Cannula (Fig. 36-47).

3. With fluoroscopic guidance, advance the Distal Rod until the threads engage in bone.

4. Rotate the Rod Driver clockwise while applying pressure to engage and advance the Rod through the sacrum. Continue advancing the Rod under fluoroscopic guidance until the portals of the rod are within in the L4-L5 disc space.

Figure 36–47 Selected implant through the Exchange Cannula.

NOTE: Once the distal end of the rod is engaged into the L4 vertebral body, the .092-inch Guide Pin can be removed.

L5-S1 implant selection

The proximal rod size selection is based on the placement of the distal rod. The measurement is taken from the base of the distal rod to the face of the sacrum, as follows:

1. Under fluoroscopic guidance, insert the .092-inch Guide Pin all the way through the disc space and up to the proximal end of the Distal Rod. Use a small clip or clamp to mark the location on the Guide Pin where it comes out of the Exchange Cannula (Fig. 36-48).

2. Slowly withdraw the Guide Pin under fluoroscopy until the Guide Pin tip is located at the face of the sacrum. Use a small clip or clamp to mark the location on the pin where it comes out of the Exchange Cannula (Fig. 36-49).

3. Use the graduation marks every 10 mm on the Guide Pin to assist in measuring. The distance between the two clamps can now be measured.

4. Select the implant size closest to the measured length (25 mm or 30 mm). The sizing of the proximal rods is based on the length of the thread portion that will engage across the L5-S1 disc and into the S1 vertebral body. The nonthreaded portion is universal and will engage all distal rods.

5. Once the implant is selected, remove the clamps from the Guide Pin and return the Guide Pin to its position within the Distal Rod.

Figure 36–48 A clamp marking the location of the Guide Pin where it comes out of the Exchange Cannula.

Figure 36–49 Use of the .092-inch Guide Pin to locate the face of the sacrum and mark it with a clamp.

L5-S1 implant placement

1. Attach the selected implant to the Rod Driver, and advance both together over the .092-inch Guide Pin and into the Exchange Cannula.

2. Using fluoroscopic guidance, carefully advance the 2-Level Proximal Rod until it engages the sacrum. Rotate the Rod Driver clockwise while applying pressure to engage and advance Rod into the sacrum.

3. Continue advancing the Proximal Rod into the sacrum, through the L5-S1 disc space, and into the proximal end of the Distal Rod.

4. Once the Proximal Rod taper is fully engaged with the Distal Rod, continue rotating until the desired distraction height is reached. Distraction of the L5-S1 disc space depends on the rotation of the Proximal Rod once it is engaged with the Distal Rod (Fig. 36-50).

5. Remove the Rod Driver and Guide Pin when desired positioning of the Proximal Rod is achieved (Fig. 36-51).

Figure 36–50 Proximal Rod engagement.

Figure 36–51 Final construction.

Step 8: Graft Material

If additional Graft Material is desired after implant placement, prepare the material into a flowable consistency that can be delivered from a standard syringe. Then inject it as follows:

1. Attach the Material Inserter onto a standard syringe. Load the material into the syringe.

2. Thread the distal end of the Material Inserter into the Rod.

3. Inject the material until the disc space is completely filled (see Fig. 36-32), and remove the Material Inserter.

Step 9: Plug Insertion

The Plug crosses the portals used to inject the material, thereby obstructing the return of any material to the interior of the Rod.

1. Attach the Plug to the Plug Driver.

2. Thread the Plug into the Rod until tight, and remove the Plug Driver.

Step 10: Finish and Close

1. Flush and aspirate as needed with antibiotic according to standard procedure.

2. Remove the Exchange Cannula and Fixation Wire simultaneously.

3. Close the skin in routine fashion, and apply a dressing to the access site.

4. Complete the 360-degree construct via posterior instrumentation with legally marketed pedicle screws or facet screws.

Potential Complications and Management

The complications and management are the same described in this chapter for AxiaLIF at one level.

Case Series [19]

In a prospective single-center clinical trial, 10 patients with a median age of 51.6 years (range 29-70 years) underwent axial lumbosacral surgery in two levels. Subjects were evaluated preoperatively as well as at discharge and postoperatively at 1 and 6 weeks, and 3, 6, 12, and 24 months. Analysis consists of measurement of disc height and fusion through radiographs and CT evaluation by an independent radiologist. Pain assessment

CASE STUDY 36.2

A 38-year-old man had axial pain with 2 years’ evolution. Results of a discogram were positive at L4-L5 and L5-S1. MRI and lateral radiographs showed spondylolisthesis grade I as well as narrowing and desiccation of the L5-S1 disc space with Modic II changes (Fig. 36-52A). The patient underwent the AxiaLIF 2L Procedure. Radiographs performed 12 months after surgery demonstrated solid fusion of L4-L5 and L5-S1, and CT scanning confirmed solid fusion of the L4-L5 and L5-S1 interspaces (Fig. 36-52B to D).

Figure 36–52 Case Study 36.2: (A) Preoperative sagittal magnetic resonance image and lateral radiograph show a black disc L4-L5 with spondylolisthesis grade I and a narrowing and desiccation of the L5-S1 disc space with Modic II changes. (B) Postoperative anteroposterior and lateral radiographs shows solid fusion of the L4-L5 and L5-S1 interspaces 12 months after surgery. (C) One year postoperatively, sagittal and coronal computed tomography scans show solid fusion of the L4-L5 and L5-S1 interspaces. (D) Three-dimensional reconstruction shows fusion at both levels.

was conducted by means of the Visual Analog Scale (VAS), Oswestry Disability Questionnaire, and SF-36 Health Survey.

Fixation of lumbosacral junction was performed through a 14-mm access cannula using an axial presacral approach. Treatment of the patients 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 stabilization and fusion approach was accomplished through three small incisions. Mean surgical time was 130.7 minutes.

There was minimal post-operative pain. The preoperative mean VAS of 9.2 (SD 0.90) had decreased to 2.2 (SD 1.2) at 12 months’ follow-up. The mean Oswestry Disability Index decreased from 63.3% (SD 18.5) to an average of 17.6% (SD 6.5) at 12 months’ follow-up. All data were statistically significant (P = 0.05). Six months after surgery, the rate of fusion was 60% (6 patients) and at 12 months’ follow-up, the fusion rate had increased to 90% (9 patients). The other patient appeared to be developing bridging bone. The overall satisfaction rate of the patients was 100%.