The patient is placed into a radiopaque bendable surgical table in a direct lateral decubitus position (90°), perpendicular to the table, with the trochanter directly positioned over the table break and with legs and knees slightly bent. Patient is then attached to the table by four adhesive strips: (1) torso, (2) iliac crest, (3) leg and knee, (4) knee and foot (Fig. 16.2). This configuration increases the space between iliac crest and ribs, especially relevant when accessing thoracolumbar junction or L4–L5 level.

To confirm the ideal positioning, fluoroscopy is used to ensure that when at 0°, the C-arm provides a true anteroposterior (AP) image, and when at 90°, a true lateral image. It is substantial that the lateral fluoroscopic images show both vertebral plateaus and superior pedicles aligned, presented as a single line, and that the AP image reveals the spinous processes in a middle position, and pedicles as circumferences (Fig. 16.3).

It is recommended to identify into the skin the iliac crest, the transition between the last rib and the posterior abdominal wall muscle and the quadratus lumborum muscle. After skin asepsis, the central position of the targeted disc can be identified using two Kirschner wires and lateral fluoroscopic images (Fig. 16.4). Then, a mark is made on the side of the patient, covering the center of the affected disc space. A longitudinal skin incision is made, over the intersection between the posterolateral muscles of the abdominal wall (abdominal internal oblique, abdominal external oblique, and transverse abdominus). A first fascia incision is made posteriorly to allow the surgeon to introduce the index finger into the retroperitoneal space and gently create a pathway and ensure that all attachments of the peritoneum are released, providing a safe lateral entry. Once identified the retroperitoneal space, a second fascia incision in made below the first skin mark to introduce the initial dilator. The index finger will safely escort the dilator up to the psoas muscle, protecting intra-abdominal contents (Fig. 16.5).

The first dilator is then placed over the surface of the psoas muscle, upon the posterior third of the disc, confirmed by AP and lateral fluoroscopy. The fibers are gently separated by the initial blunt dilator until the side surface of the disc be reached, with concomitant EMG monitoring for assessing the closeness to the lumbar plexus (Fig. 16.5). The dilator can be rotated in position to determine not just proximity, but also the direction of nerves. Larger dilators are placed in sequence over the previous, always checking the EMG, until the final placement of the three blades retractor, still closed. The retractor is connected to a suspension arm in order to prevent unwanted movement. After confirming the ideal position by fluoroscopy, the working portal can be selectively adjusted to the desired diameter. A bifurcated optical fiber cable is attached to the retractor for optimal direct visualization of the exposure (Fig. 16.6).

In patients with spondylolisthesis, the meticulous realization of the procedure is essential to avoid neurological deficit, as the neural structures are shifted ventrally by the L4 vertebral body slipping [19]. Moreover, the retractor opening must be minimal, with the shorter duration of muscle spreading as possible, since the lumbar plexus must be compressed during psoas traverse.

Under direct visualization, a wide discectomy is performed with standard instruments. The anterior and posterior portions of the disc containing the longitudinal ligaments are preserved with discectomy focused in the center of the disc, with a sufficient AP dimension to accommodate a large implant. Laterolateral disc removal and contralateral ring release with a Cobb are essential to ensure symmetrical distraction, properly bilateral decompression and avoid coronal iatrogenic changes. Furthermore, this maneuver offers the opportunity to place an implant that covers both side edges of the cortical apophyseal ring, maximizing the spinal plateau support (Fig. 16.7). The complete removal of cartilage and rasping the cortical bone layer are essential to providing blood precursor cells and bone growth factors for the successful bone ingrowth.

In spondylolisthesis, the accurate discectomy itself partially reduces the vertebral slippage. The maintenance of the anterior and posterior portions of the disc, keeping intact the longitudinal ligaments, allows ligamentotaxis, partly responsible for slippage reduction and indirect decompression of the neural structures [13, 14, 28].

To determine the correct spacer to be inserted, implant proofs of height, length, and angle should be inserted into the disc space to find the most suitable for the stipulated objectives, guiding the entire process by fluoroscopic imaging. The ideal placement of the device is centered across the disc space from an AP view, and between the anterior third and middle third of the disc space from a lateral view. The ideal implant positioning also restores focal lordosis, usually lost in this kind of deformity, especially at L4–L5 [15].

As a minimally invasive option, it is recommended to use synthetic bone grafts instead of autologous bone, avoiding major postoperative morbidity. The final position of the implant must be checked on AP and lateral fluoroscopy.

After washing the surgical site, the retractor is closed and slowly removed in order to observe the psoas muscle closure and confirm hemostasis. The incisions are closed in a standard fashion and no drain is required. The construct may be supplemented with the internal fixation system of choice, when indicated.

Patients should be encouraged to walk the same day to aid their recovery and muscle function, also avoiding deep venous thrombosis and pulmonary thromboembolism. Postoperative pain tends to be minimal, and patients may be discharged after only an overnight hospital stay. Literature shows low rate of complications in the immediate postoperative period, including hip flexion weakness (psoas weakness) or numbness ipsilateral to the surgical access (plexopaties), and less frequently quadriceps transitory weakness, the great majority resolved within 6 months [13, 15, 29, 30].