Three-dimensional Navigation-guided, Prone, Single-position, Lateral Lumbar Interbody Fusion Technique

NOTE: The protocol follows the guidelines of and was approved by the Brigham human research ethics committee.

1. Equipment and positioning

1. Use an open Jackson table for the procedure. Ensure the availability of both frameless stereotactic navigation and intraoperative neuromonitoring with lower extremity electromyography (EMGs), which are critical to the success of the case.
   ​NOTE: An open Jackson table allows the abdominal viscera to fall away from the spine during the lateral approach.
2. Place the patient in the prone position with legs extended. Pay special attention to the hip and/or thigh pads on the side that the interbody spacer will be introduced. If required, shift these pads caudally before the procedure begins if they crowd into the anticipated lateral entry point below the patient's lowest ribs.

2. Initial posterior approach and posterolateral instrumentation

1. Expose the posterior elements first via a midline incision over the target levels. Open the fascia in standard fashion, and dissect the paraspinal musculature off the bony elements, including the eventual pedicle screw entry points. Next, place a spinous clamp and have the radiology technician bring in the O-arm to obtain an intraoperative computed tomography scan to allow for stereotactic navigation.
2. Next, place pedicle screws at the appropriate levels in a standard fashion with navigation assistance.
   ​NOTE: Doing so at this step ensures that the pedicle screws are placed before the navigation is disturbed, either inadvertently during the case or intentionally by the placement of the interbody cages. Moreover, placement of the screws can aid in the lateral discectomy portion of the case.

3. Lateral approach and interbody cage placement

1. Next, start the lateral approach. Using the navigation, mark a skin incision on the flank, positioning it such that it will bring the surgeon perpendicularly across the mid-point of the target disc space (or allow for multiple such trajectories if inserting interbody cages at multiple levels).
   1. At this point, rotate the patient's bed away for a more comfortable working position for the surgeon (i.e., "airplaning"). Similarly, consider using a sitting stool to drop the surgeon's working angle to allow for a more comfortable approach (Figure 1).
2. Make a 2'' to 3'' incision in the patient's flank, parallel to the patient's ribs. Dissect through the subcutaneous fat and external oblique fascia using electrocautery. Next, dissect with a pair of Metzenbaum scissors to spread open the external oblique, internal oblique, and transverse abdominus muscles and gain access to the retroperitoneal space.
3. Once the potential retroperitoneal space is encountered, use fingers for blunt dissection of the space to feel the peritoneal cavity pulling away through the force of gravity and then rapidly encounter the bulk of the psoas muscle overlying the spine. Feel the transverse process as a landmark posteriorly. Use fingers for further blunt dissection to separate the retroperitoneal cavity more thoroughly from the lateral spine surface, especially in the cranial-caudal direction to minimize the chance of inadvertently entering the peritoneal cavity in the subsequent steps.
4. Next, place a table-mounted, lighted, lateral-access retractor system just superficial to the psoas muscle (Figure 2).
   1. To enter the psoas, first, use a navigation-guided fenestrated probe to select an optimal entry point and approach angle into the target disc space. Then, place A K-wire through the fenestrated probe into the disc space to secure the access.
   2. Place sequential dilators over the probe superficial to the psoas muscle until finally, the table-mounted retractor system is brought in and secured.
   3. Connect the light source to the retractor blades. Then, open the retractor blades in the cranial-caudal and anterior-posterior directions to visualize the surgical area directly.
5. Next, dissect the psoas muscle under direct vision using long Panfield 4 and long Kittner dissectors to expose enough disc space to accommodate the width of the cage (generally 18 mm). If required, use EMG monitoring to monitor the lumbosacral space.
   NOTE: Under direct vision, the lumbosacral plexus nerves traveling on the surface of the psoas muscle are easily identified and avoided to minimize injury to those nerves. Traversing the psoas in a separate step, under direct vision with the lighted retractor system, allows for greater ability to avoid damage to the lumbosacral plexus.
   1. Once the disc space is fully exposed, place two pairs of pins in the cranial and caudal vertebral bodies to keep the surgical corridor through the psoas muscle open.
      NOTE: The pins keep the psoas muscle (and the associated plexus nerves) clear of the surgical corridor, thus providing a comfortable and safe surgical environment. It eliminates the muscle creeping problem commonly encountered with the expandable tubular retractor system (Figure 3).
6. Ensure that the disc space is adequately exposed in both the cranial-caudal and the anterior-posterior dimensions. Perform an annulotomy with a #15 blade, and perform an initial discectomy using pituitary rongeurs and curettes.
   1. During this step, break the annulus on the contralateral side using a navigated cobb elevator to release the space and facilitate a larger interbody cage placement and scoliosis correction when needed.
      1. Insert the navigated cobb elevator into the disc space. Under the navigation guidance, advance the tip of the cobb elevator beyond the contralateral disc border and "pop" it through the contralateral annulus for annulus release.
         NOTE: Due to the cobb elevator being navigated, the location of the tip of the cobb elevator can be tracked at all times. Therefore, take care not to violate the annulus on either the anterior or posterior side to protect the great vessels and the thecal sac, respectively.
   2. Of note, with simultaneous access to the posterior spine while this is going on, place the pedicle screws in distraction at this time if needed.
      NOTE: This not only facilitates entrance into particularly narrow and collapsed disc spaces but also allows for the placement of a larger interbody spacer than would be possible otherwise.
7. Afterwards, use sequentially larger navigated shavers and navigated cage trials to prepare the disc space further. Take care to avoid violating the bony endplates. Once an appropriately sized cage trial is determined, insert the corresponding interbody cage (Conduit lateral Interbody cage) with navigation guidance (Figure 4). Before inserting the cage, fill the cage with allograft bone chips or any grafting materials of the surgeon's choice.
8. Remove the pins holding back the psoas muscle and achieve hemostasis. At this point, shift the lighted retractor system to another target level if multiple interbody cages are intended to be placed. Otherwise, remove the system and close the muscle, fascia, and skin in a layered fashion.

4. Completion of the posterior portion

1. Should further posterior decompression be needed (e.g., laminectomy), perform it at this point.
   ​NOTE: This can also be performed simultaneously during some portions of the lateral procedure if a second qualified operator is available (Figure 1).
2. Finally, place rods to connect the pedicle screws, decorticate the spine, and place a morselized bone graft in a standard fashion. Routinely place vancomycin powder in the cavity, place wound drains, and use liposomal bupivacaine in the back musculature. Perform the closure in the standard layered fashion, including muscle, fascia, subcutaneous tissues, and skin.
   NOTE: Closure can be performed simultaneously with the closure of the lateral incision should it fit with the workflow of the individual case.