MIS: Venu M. Nemani and Oheneba Boachie-Adjei
Open: John D. Koerner and Todd J. Albert

Arthrodesis at the lumbosacral junction is the treatment of choice for a wide variety of spinal diseases, including but not limited to trauma, instability, tumor, deformity, and degenerative conditions. While spinal fusion can be performed via a variety of approaches and techniques, obtaining an interbody fusion is often desirable due to the favorable biomechanical environment and the ability to achieve indirect foraminal decompression and restoration of sagittal alignment via restoration of intervertebral height. Interbody fusions can be performed via several different approaches, all with their own unique advantages and disadvantages. The traditional open approaches include anterior lumbar interbody fusion (ALIF), posterior lumbar interbody fusion, and transforaminal interbody fusion.

The indications for combined interbody and posterolateral fusion include painful disc degeneration after the failure of nonoperative treatment, low- or high-grade spondylolisthesis, and revision surgery for failed posterior fusion. Interbody support is also important at the lumbosacral junction below long fusion constructs for adult idiopathic or degenerative scoliosis. Degenerative disc disease (DDD) is usually confirmed radiographically by decreased disc height and signal changes within the disc.

The benefits of the presacral approach versus ALIF include avoidance of a traditional transperitoneal or retroperitoneal dissection, which can be complicated by vessel injury, retrograde ejaculation, and postoperative ileus. The presacral approach also preserves the anterior longitudinal ligament and the anterior annulus, both of which are critical to the stability of the motion segment. Furthermore, the approach involves minimal dissection and is muscle-sparing, which theoretically can minimize postoperative pain. Lastly, the AxiaLIF implant (Baxano Surgical; Raleigh, NC) is unique in that it resists the shear stresses that predominate at the lumbosacral junction in cases of spondylolisthesis. The AxiaLIF rod thus resists anterior translation at L5–S1 and protects the posterior pedicle screw fixation, while an ALIF cage or graft alone does not.

Before considering presacral interbody fusion, patients receive a magnetic resonance imaging (MRI) of the pelvis to ensure there is a safe fat plane devoid of vascular structures separating the visceral peritoneum from the anterior sacral wall, to allow for an appropriate corridor to pass the implant. This percutaneous procedure is contraindicated in patients with extensive vasculature in this plane or those who have retroperitoneal scarring from previous procedures.

Patients undergo a standard bowel prep using GoLYTELY. Patients are positioned prone on a flat Jackson table with all bony prominences well padded. In this case, we would begin with a standard midline posterior approach to the spine for reduction and instrumentation of L5 and S1 with pedicle screws. Reduction of the spondylolisthesis is achieved by bringing the spine to bilateral rods fixed distally. The facet joints and transverse processes are decorticated, and local bone graft and graft extenders are placed to encourage a posterolateral fusion. The posterior procedure could also be performed in a minimally invasive fashion using percutaneous screws.

Presacral interbody fusion can proceed using the same prone patient positioning without a separate prep and drape; however, in practice, we usually close and dress the posterior wound and reposition the patient with an additional pillow underneath the hips to maximize hip flexion. Two C-arms are needed to obtain simultaneous AP and lateral views. We also usually exclude the previous wound from the surgical field to minimize risk of contamination.

A 3-cm transverse incision is made on the right buttock next to the coccygeal area. We utilize a transverse incision because it reduces the risk of wound dehiscence with sitting. The ligamentous fascia is exposed bluntly to the presacral region using a curved Kelly clamp turned toward the anterior surface of the sacrum. Next, under fluoroscopy, a blunt dissecting tool is then advanced along the midline of the sacrum to the S1–S2 level. Then, the inner blunt stylet is exchanged for a guide pin that is tapped into the S1 vertebral body, across the L5–S1 disc space, and 1 to 2 mm into the L5 vertebral body under fluoroscopic visualization. A series of dilators are then passed over the guide pin to dilate the sacral implant tract. A working cannula is then secured into place to allow for drilling of an osseous path from the anterior sacrum through S1 into the L5–S1 disc space. The discectomy is then performed using radial and down-cutting blades. The disc space is then typically packed using local bone and a graft extender, with our preference being cancellous allograft chips. If the disc space is felt to be relatively large, then 2-mg bone morphogenetic protein (BMP; without a collagen sponge) mixed with demineralized bone matrix and local bone is used to pack the disc space. The discectomy is followed by insertion of exchange cannulas to allow passage of the threaded AxiaLIF rod. A nondistracting rod is used when posterior fixation is performed as the first stage and no further distraction is needed. Closure is performed in layers as per routine.

The patient is placed in the supine position. After induction of general anesthesia and placement of an endotracheal tube, the abdomen is prepped and draped. A low transverse incision is made through the skin and subcutaneous tissue, the fascia is divided, and rectus muscles are split in the midline. The preperitoneal and left-sided retroperitoneal space is entered. The L5– S1 disc space is approached at the confluence of the iliac veins. At this level, mobilization of the vascular structures may not be necessary, other than the middle sacral vessels. An X-ray marker is placed and confirms the appropriate level. After incising and removing the disc, a curette is used to gently remove the cartilaginous end plates of the vertebral bodies above and below the interspace. After squaring off the end plates, a rasp is used to further refine and smooth the end plates and to expose bleeding bone across both surfaces. In addition to allograft, a variety of interbody implants are available today, including threaded interbody devices, lumbar tapered devices, PEEK (polyetheretherketone) cages, and titanium mesh cages. Regardless of the device chosen, appropriate sizing and placement is key, ideally countersunk a few millimeters, without protruding posteriorly. Imaging is obtained to confirm appropriate positioning within the disc space. The rectus is then reapproximated with Vicryl sutures, and the fascia is closed with running #1 PDS suture. Subcutaneous tissue is reapproximated with 3–0 Vicryl suture, and the skin is closed with a running subcuticular closure.