Background: 

Lateral lumbar interbody fusion (LLIF) is a widely utilized minimally invasive surgical procedure for anterior fusion of the lumbar spine. However, posterior decompression or instrumentation often necessitates patient repositioning, which is associated with increased operative time and time under anesthesia1–3. The single-position prone transpsoas approach is a technique that allows surgeons to access both the anterior and posterior aspects of the spine, bypassing the need for intraoperative repositioning and therefore optimizing efficiency4. The use of robotic assistance allows for decreased radiation exposure and increased accuracy, both with placing instrumentation and navigating the lateral corridor.

Description: 

The patient is placed in the prone position, and pedicle screws are placed prior to interbody fusion. Pedicle screws are placed with robotic guidance. After posterior instrumentation, a skin incision for LLIF is made in the cephalocaudal direction, orthogonal to the disc space, with use of intraoperative (robotic) navigation. Fascia and abdominal muscles are incised to enter the retroperitoneal space. Under direct visualization, dilators are placed through the psoas muscle into the disc space, and an expandable retractor is placed and maintained with use of the robotic arm. Following a thorough discectomy, the disc space is sized with trial implants. The expandable cage is placed, and intraoperative fluoroscopy is utilized to verify good instrumentation positioning. Finally, posterior rods are placed percutaneously.

Alternatives: 

An alternative surgical approach is a traditional LLIF with the patient beginning in the lateral position, with intraoperative repositioning from the lateral to the prone position if circumferential fusion is warranted. Additional alternative surgical procedures include anterior or posterior lumbar interbody fusion techniques.

Rationale: 

LLIF is associated with reported advantages of decreased risks of vascular injury, visceral injury, dural tear, and perioperative infection5,6. The single-position prone transpsoas approach confers the added benefits of reduced operative time, anesthesia time, and surgical staffing requirements7. Other potential benefits of the prone lateral approach include improved lumbar lordosis correction, gravity-induced displacement of peritoneal contents, and ease of posterior decompression and instrumentation8–11. Additionally, the use of robotic assistance offers numerous benefits to minimally invasive techniques, including intraoperative navigation, instrumentation templating, a more streamlined workflow, and increased accuracy in placing instrumentation, while also providing a reduction in radiation exposure and operative time. In our experience, the table-mounted LLIF retractor has a tendency to drift toward the floor—i.e., anteriorly—when the patient is positioned prone, which may, in theory, increase the risk of iatrogenic bowel injury. The rigid robotic arm is much stiffer than the traditional retractor, thereby reducing this risk.

Expected Outcomes: 

Compared with traditional LLIF, with the patient in the lateral and then prone positions, the single-position prone LLIF has been shown to have several benefits. Guiroy et al. performed a systematic review comparing single and dual-position LLIF and found that the single-position surgical procedure was associated with significantly lower operative time (103.1 versus 306.6 minutes), estimated blood loss (97.3 versus 314.4 mL), and length of hospital stay (1.71 versus 4.08 days)17. Previous studies have reported improved control of segmental lordosis in the prone position, which may be advantageous for patients with sagittal imbalance18,19.

Important Tips:  Adequate release of the deep fascial layers is critical for minimizing deflection of retractors and navigated instruments. The hip should be maximally extended to maximize lordosis, allowing for posterior translation of the femoral nerve and increasing the width of the lateral corridor. A bolster is placed against the rib cage to provide resistance to the laterally directed force when impacting the graft. The cranial and caudal limits of the approach are bounded by the ribcage and iliac crest; thus, surgery at the upper or lower lumbar levels may not be feasible for this approach. Preoperative radiographs should be evaluated to determine the feasibility of this approach at the intended levels. When operating at the L4-L5 disc space, posterior retraction places substantial tension on the femoral nerve. Thus, retractor time should be minimized as much as possible and limited to a maximum of approximately 20 minutes20–22. A depth of field (distance from the midline to the flank) of approximately 20 cm may be the limit for this approach with the current length of retractor blades19. In robotic-assisted surgical procedures, minor position shifts in surface landmarks, the robotic arm, or the patient may substantially impact the navigation software. It is critical for the patient and navigation components to remain fixed throughout the operation. In addition to somatosensory evoked potential and electromyographic monitoring, additional motor evoked potential neuromonitoring or monitoring of the saphenous nerve may be considered22. In the prone position, the tendency is for the retractor to migrate superficially and anteriorly. It is critical to be aware of this tendency and to maintain stable retractor positioning. Acronyms and Abbreviations:  LLIF = lateral lumbar interbody fusion MIS = minimally invasive surgery PTP = prone transpsoas y.o. = years old ASIS = anterior superior iliac spine PSIS = posterior superior iliac spine ALIF = anterior lumbar interbody fusion TLIF = transforaminal lumbar interbody fusion MEP = motor evoked potential SSEP = somatosensory evoked potential EMG = electromyography CT = computed tomography MRI = magnetic resonance imaging OR = operating room POD = postoperative day IVC = inferior vena cava A. = aorta PS. = psoas