Preoperative planning

As is appropriate for all patients who undergo a surgical procedure, we recommend preoperative medical and cardiovascular evaluations. In addition, preoperative radiographs help define potential problems with the approach trajectory. For example, if the operative level will be L4-L5, the height of the iliac crest should be checked to see that there will be clearance into the disc space. All L4-L5 levels can be accessed laterally with appropriate patient positioning on a bendable surgical table. At upper levels, determination of rib location helps prevent any unsuspected surprises during the approach. At L1-L2, either the lower rib may need to be elevated superiorly away from the approach or an intercostal approach may be necessary.

Indications

Indications for the XLIF technique are the same as those for any interbody fusion, with the limitation of access only at disc levels above L5. Such patients typically suffer discogenic pain due to segmental instability, disc degeneration, degenerative scoliosis, and/or grade I or II spondylolisthesis [2–7]. It may also be applied to patients in whom prior decompressive surgery (i.e., discectomy and/or laminectomy) have failed and who therefore require interbody fusion, and in cases of adjacent-level disease after prior fusion surgery, because in these revision cases, scarring may limit the ability to safely perform a more traditional fusion approach. Revisions of failed interbody fusions and failed lumbar total disc replacements have also been treated with the XLIF approach for retrieval and revision.

The XLIF approach has been successfully accomplished for levels above and including L4-L5. Approaching the L5-S1 level with this technique is not recommended because of the risk of damage to the iliac blood vessels as well as the difficulty of accessing the disc space because of the iliac crest. For the L5-S1 level, it is easier to use a mini-open retroperitoneal approach or minimally invasive posterior approach.

Instrumentation

The instruments necessary for performing the XLIF procedure are as follows:

MaXcess System of dilators and split-blade retractor (Fig. 37-2A; NuVasive, Inc.). Consists of bifurcated light cable, articulating arm, retractor system with various length blades, and blade-extension shims.

NeuroVision System for MaXcess-compatible stimulated and continuous electromyography (EMG) monitoring of nearby nerves (Fig. 37-2B; NuVasive, Inc.).

Set of interbody instruments, such as curettes, Kerrison rongeurs, and dissectors of different sizes (available within XLIF and General Instrument Sets, NuVasive, Inc.).

Light source for attachment to MaXcess bifurcated light cable.

Radiotransparent surgical table with a flexible middle section and rail for attachment of articulating arm.

C-arm fluoroscope and image intensifier.

Figure 37–2 (A) MaXcess System of dilators and split–blade retractor (NuVasive, Inc., San Diego, CA). (B) NeuroVision System for the MaXcess System.

Surgical technique

Patient Preparation

In the preoperative waiting area, the patient is prepared for NeuroVision EMG monitoring; four muscle groups per side can be monitored using the NeuroVision System. These four muscles are easily palpated and represent spinal nerve distributions from L2-S2: the vastus medialis, the anterior tibialis, the biceps femoris, and the medial gastrocnemius (Fig. 37-3). A reference electrode is also placed on the upper lateral thigh, and an anode return electrode is placed superior to the operative site, such as on the latissimus dorsi muscle.

Figure 37–3 Anterior and posterior placement of electrodes for NeuroVision EMG monitoring (NuVasive, Inc., San Diego, CA). Gastroc, gastrocnemius.

Proper skin preparation must be performed to ensure good electrical conductivity with the skin. This entails cleaning the electrode site and applying a light abrasive to remove dead skin cells. Electrodes are placed in pairs by simple removal of the adhesive backing and application to the skin. Electrical conductivity can be measured with a handheld impedance meter. These surface electrodes are connected to the NeuroVision System by snap-on cables that can be threaded under or through small holes in compression stockings.

Patient Positioning

1. The patient’s written informed consent is obtained.

2. The patient is placed on a bendable surgical table in a direct lateral decubitus (90-degree) position so that the greater trochanter is directly over the table break.

3. The patient is then secured with tape just below the iliac crest, over the thoracic region, from the iliac crest across the knee and to the table, and from the table to the knee, past the ankle, then to the table. This configuration ensures that the pelvis tilts away from the spine, allowing access to all lumbar levels, particularly L4-L5.

4. With use of fluoroscopy (C-arm) to verify location, the surgical table should be flexed to increase the distance between the iliac crest and the ribs in order to gain direct access to the disc (Fig. 37-4).

5. Once the patient is secured, the table is adjusted so that the C-arm provides true anteroposterior (AP) images when at 0 degrees and true lateral images when at 90 degrees. The table should be adjusted independently when each level is accessed in order to maintain this relationship.

Figure 37–4 Lateral decubitus patient positioning with elevation and elongation of space between the ribs and iliac crest. Schematic drawing of patient’s position (top) and corresponding intraoperative picture (bottom).

Incision Placement and Dissection

1. After aseptic treatment of the skin, a mark is made on the patient’s side, overlying the area to be implanted. The exact location of the mark is guided via fluoroscopy with the use of two Kirschner wires held over the skin to target the disc being approached (Fig. 37-5A). One line is drawn in an anteroposterior direction, over the center of the disc that is to be operated. Another line is drawn in a superoinferior direction, crossing the center of the neighboring vertebral bodies.

2. The skin incision is made where these lines cross, and through this opening, the dilators and expandable retractor will be inserted (Fig. 37-5B).

3. A second mark is made posterolaterally in the depression formed by the margin of the paraspinal muscles and external oblique muscles. Through this opening the surgeon’s index finger will be inserted to help guide placement of the initial dilators.

4. At this mark, a longitudinal incision of approximately 2 cm is made. The layers of the lateral abdominal muscles are identified and opened one by one (external oblique, internal oblique, transversus, and the transversal fascia) until the retroperitoneal fat is reached (Fig. 37-6A). This dissection is performed with the help of scissors and by palpation of the muscle layers at each level.

5. After dissection has passed through the fascia and the retroperitoneal space has been accessed, the index finger is used to dissect through the retroperitoneal fat, sweeping both deep and back up toward to the skin (Fig. 37-6B), to open the retroperitoneal space above the psoas muscle. Special care should be taken to avoid perforation of the peritoneum.

6. The procedure continues by making an incision of approximately 3 cm at the first skin mark (the one that represents the targeted disc space) through which the first MaXcess dilator will pass. The placement of this device is guided by the surgeon’s index finger, which is already in the retroperitoneal space, in order to avoid injuring vascular or intestinal tissues (Fig. 37-7A).

7. The muscle dilators are passed to rest on the portion of the psoas muscle overlying the disc space to be operated on. To confirm this position, anteroposterior and lateral fluoroscopy is performed (Fig. 37-7B).

8. Once proper positioning of the dilators is confirmed, the MaXcess dilators are delicately passed through the psoas muscle fibers, with use of NeuroVision (i.e., neural guidance attached to the dilators for evoked EMG monitoring of the relative distance to nerves) until the surface of the disc is reached (Fig. 37-7C). NeuroVision should confirm that the nerves are posterior to the dilator.

Figure 37–5 A) Fluoroscopic guidance of direct lateral incision site. Operative target (the center of X line) is the center of the intervertebral disc. (B) Skin markings showing the direct lateral incision site for the working instruments and the posterolateral incision site for the initial retroperitoneal finger dissection. DIRECT LATERAL INCISION (right side) and POSTEROLATERAL INCISION (left side).

Figure 37–6 Retroperitoneal finger dissection. (A) Blunt approach to the retroperitoneal space through the layers of the lateral musculature. (B) Sweeping of the retroperitoneal space, both deep and back toward the direct lateral incision site.

Figure 37–7 Access to the disc space: (A) Retroperitoneally located finger gently guides the initial dilator to the surface of the psoas muscle, protecting the peritoneum from impingement. (B) Placement of the initial dilator over the center of the disc is confirmed with fluoroscopy. (C) The initial dilator is connected to NeuroVision EMG monitoring (upper left inset) prior to its advancement through the psoas muscle. Low EMG thresholds indicate nearby nerves; higher thresholds indicate safe passage. Circle, the connection between NeuroVision and dilator. (D) Two subsequent dilators are passed over the first, each guided by NeuroVision EMG. Afterwards the split–blade retractor is advanced over the last dilator and opened to a customizable aperture. An articulating arm is attached to the retractor at the posterior blade and to the table, holding the retractor rigid preventing posterior excursion of the retractor during expansion, thereby protecting the nerves within the psoas muscle from compression injury. (E) A bifurcated light attachment is fixed through the blades of the retractor (left), providing deep illumination for direct visualization (right). (E1) and (E2) are black and white images, and (E3) is the completed process.

The dilator is rotated in position to determine not just proximity, but also direction of the nerve. A mark at the proximal end of the dilator corresponds to the location of an isolated electrode at the distal end. If low thresholds result, the dilator should be removed from the muscle, and moved slightly more anterior to find a new trajectory through the psoas muscle where higher thresholds are achieved.

9. Both anteroposterior and lateral fluoroscopy should be used to ensure correct targeting of the disc space. Once the disc is reached, another confirming fluoroscopic image is obtained, and the position is held by placement of a Kirschner wire into the disc space.

This entire process produces only minor trauma to the psoas muscle and minimizes the potential for transitory deficit in the patient’s ability to flex the hip.

10. Sequentially larger MaXcess dilators are then introduced (Fig. 37-7D), gradually and bluntly spreading the psoas muscle fibers until insertion of the expandable retractor, which can be selectively adjusted to the desired diameter (Fig. 37-7E).

11. The retractor is connected to the suspension arm of the MaXcess System in order to prevent unwanted movement (Fig. 37-7F). The arm attaches to the retractor’s posterior blade, preventing posterior expansion and thereby protecting the nerves in the posterior region of the psoas muscle from compression injury.

12. A bifurcated light cable is attached to the retractor for optimal direct visualization of the exposure (Fig. 37-7G). If necessary, either one or both of the cephalocaudal blades can be angled open further. This further opening expands the distal part of the exposure and may be helpful to preferentially adjust the exposure in either direction (e.g., inferiorly at L4-L5 under the iliac crest) to gain optimal access to the disc space.

Care should be taken to avoid expanding the blades to the mid-vertebral body, to minimize psoas trauma and risk of segmental vessel injury. Exposure needs to be only as wide as the disc space.

Preparing the Disc

With the MaXcess retractor in place, the remainder of the procedure is conventional—disc removal, endplate preparation, and implant insertion, as follows:

1. Any tissue debris on the lateral surface of the disc is retracted or coagulated.

2. An anulotomy is created at least 18 mm long (anterior to posterior).

3. A Cobb elevator is passed along both end plates and completely through the contralateral anulus. This step is critical to facilitate distraction of the disc space, achieve proper coronal alignment, and place a large implant that spans the ring apophysis.

4. Pituitary rongeurs, curettes, disc cutters, scrapers, and other disc preparation instruments are used to thoroughly evacuate the disc and prepare the end plates for fusion (Fig. 37-8a,b).

Figure 37–8 With the approach accomplished and the retractor open, the interbody work is conventional, consisting of disc removal, end plate preparation, and implant insertion.

Device Implantation

1. After the disc has been prepared, the device is inserted.

2. First the vertebrae are distracted and the dimensions of the implant are determined. Verify proper anteroposterior position should be verified with lateral fluoroscopy.

3. The implant is introduced from a lateral direction into the disc space. This entire process is guided by fluoroscopic imaging. A large implant that expands across the disc space to provide end plate coverage on the periphery of the ring apophysis is ideal (Fig. 37-9).

Figure 37–9 The XLIF implant (NuVasive, Inc., San Diego, CA) spans the ring apophysis, providing maximum vertebral support.

The ideally placed implant is centered across the disc space from a mediolateral perspective, and between the anterior and middle thirds of the disc space from an anteroposterior perspective. Implants may be filled with cancellous bone graft from the iliac crest, bone morphogenetic protein, or any osteoinductive agent of choice (Fig. 37-10). The construct may be supplemented with the internal fixation system of choice.

Figure 37–10 Anteroposterior and lateral fluorographs of an L4–L5 procedure using a long implant that provides optimal surface area for fusion and biomechanical stability.

Case Series

Between July 1998 and October 2002, prior to the availability of the MaXcess and NeuroVision Systems, we implanted fusion devices in 69 patients using the technique described [8]. We accessed 74 discs spanning the levels L1-2 through L4-L5. The level most frequently operated was L4-L5 (55, 75%), followed by L3-L4 (15, 19.4%), L2-L3 (2, 2.8%), and L1-L2 (2, 2.8%). In 64 patients (92.5%), only one level was operated, and in 5 patients (7.5%),two levels were operated. Preoperative clinical evaluation revealed that 80% of the patients presented with VAS scores above 7 having lasted for more than 6 months. Postoperatively, the clinical improvement was excellent in 58.2% of patients, and good in 19.4%, rates similar to those reported in the literature [9]. Clinical improvements occurred between 6 days and 6 months after surgery, with an average of 3 months. Complications were minor and included one ureter injury that was repaired during the same procedure and a low incidence of transient psoas weakness that typically normalized after 1 week.

According to the authors, experience with this technique since that time has incorporated the specifically designed access instruments (MaXcess System) and procedure-based EMG monitoring (NeuroVision System). Anecdotal evidence shows continued success as well as improvements in surgical time, hospital stay, recuperation, and complication rates [10].

Conclusion

We recommend the use of the XLIF approach for lumbar interbody fusion. The approach is safe and efficient, with few postoperative complications and with a short postoperative recuperative period. It is also worth noting the better aesthetic results of the operation, which requires only two small incisions, thus minimizing scarring. Because the XLIF procedure is a minimally invasive technique, depending on the state of the patient and on the type of fixation, it can require less hospitalization time, thereby helping to minimize costs as well.