Paracoccygeal Transsacral Approach to the Lumbosacral Junction for Interbody Fusion

Summary of Key Points

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The paracoccygeal transsacral approach is a minimally invasive surgical technique to achieve lumbar interbody fusion at L5-S1 or both L4-5 and L5-S1.
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The unique transsacral access to the L5-S1 disc is achieved by crossing through the avascular space anterior to the sacrum, starting distally at the tip of the coccyx and entering the sacrum at the S1-S2 junction ( Fig. 88-1 ).

Figure 88-1

Anatomy of the paracoccygeal transsacral approach at L4-5 and L5-S1. A, Normal sacral anatomy with green shading representing the trajectory and range for placement of the interbody device. B, Illustration shows entry point and device placement. C, Hyperlordotic segment unsuitable for this approach. D, Templating a trajectory for a two-level interbody device.

(Printed with permission of the Mayfield Clinic, Cincinnati, Ohio.)
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The distinct benefits offered by this procedure are most notable for minimizing damage to muscular, neural, ligamentous, and vascular structures.
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Known also as the presacral approach or AxiaLIF (axial lumbar interbody fusion), this technique was first described by Cragg and colleagues in 2004 and the instrumentation was developed by Trans1. Following clearance from the U.S. Food and Drug Administration (FDA) in 2005, this surgical technique for interbody fusion at the lumbosacral junction was introduced into clinical practice. In 2008, FDA clearance was obtained for a two-level device, allowing fusion across the L4-5 and L5-S1 segments.
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This chapter overviews the approach, discusses surgical risks and benefits, surveys the outcomes reported in the literature for the 10-year period since its inception, and examines controversial issues, perhaps affecting the adoption of this approach.

Operative Technique

Preoperative evaluation of the sacral anatomy confirms that the sacral curve is appropriate for the development of a trajectory to the L5-S1 segment and rules out any aberrant vascular anatomy in the presacral space.

After completing a bowel prep the night before, the patient is positioned prone on the operating table to maximize lordosis; the legs are abducted and a sterile barrier covers the buttocks. A small paracoccygeal incision is made and the fascia is opened. Blunt finger dissection opens the presacral plane. In a trajectory just inferior to the sacrococcygeal ligament, a guide pin is passed using fluoroscopic guidance through the presacral space and docked on the sacrum over which a series of dilators are advanced.

An entry point is chosen at the S1-S2 junction. A 12-mm channel is drilled through the sacrum, and the L5-S1 disc space is entered in its midportion. Various sharp looped and flat nitinol cutters are advanced into the disc space to morselize the disc. After evacuation of the morselized nucleus pulposis with wire brushes, the end plates are rasped in preparation for placement of bone and other grafting materials. The space is then irrigated with antibiotic solution, and the bone graft material is inserted and dispersed radially into the disc space with a beveled cannula. Through a small channel drilled into the L5 end plate, measurements are made to determine the length of the interbody device to be placed. The modular device is assembled on the back table and then advanced through a larger exchange cannula across the L5-S1 segment into its final position ( Fig. 88-2 ).

Once in place, the device can be expanded to distract the interspace, restore disc height, and in some cases improve lordosis. After the device is locked into position, the cannula is removed. Various techniques can be used to confirm the integrity of the nearby rectum, including saline or dye injection or direct visualization with a rigid proctoscope. The incision is closed in multiple layers.

Preoperative Considerations: Indications and Contraindications for the Paracoccygeal Transsacral Approach

The success of the paracoccygeal transsacral approach hinges on preoperative decisions of optimizing patient selection and evaluating the correct imaging studies. The trajectory and procedure’s feasibility are defined by overlaying a template onto the x-ray or magnetic resonance imaging (MRI) and studying the path from the coccyx tip to the midportion of the L5-S1 disc.

Indications

The presacral device can be considered for any patient who will undergo an interbody fusion with posterior fixation at L5-S1 or L4-5 and L5-S1. Indications include degenerative disc disease with or without radiculopathy, spondylolisthesis, spinal stenosis, revision surgeries postlaminectomy, and failed fusions at the L4-5 and L5-S1 segments. The device is supplemented with posterior fixation using pedicle or facet screws ( Fig. 88-3 ).

The ideal candidate has a moderate body mass index (BMI) and a classically shaped sacrum. The patient’s sacral morphology is best evaluated by standing lateral lumbar films with a full view of the sacrum; this can accurately show lordosis, both in the sacrum and of the weight-bearing lumbar spine. Vascular anatomy is assessed by MRI of the presacral space/pelvis or computed tomography angiography (CTA) of the pelvis; this confirms the lack of vascularity of the presacral space and the absence of any vascular anomaly (e.g., aberrant iliac vein crossing the S1-2 entry point). During the approach, the middle sacral artery moves anteriorly away from the sacrum as it descends caudally. Injury to this artery is rare.

A large presacral fat pad seen in obese patients provides an already larger space, but lack of any fat pad does not create an impediment because the space “opens-up” with blunt finger dissection. A T2-weighted sagittal image will identify the presence and thickness of the presacral fat. Of note, its absence in a thin person does not contraindicate the surgery because this space, devoid of fat, will be dissected open early in the procedure.

A two-level approach requires careful evaluation of the potential trajectory before scheduling the procedure. In almost all cases with a two-level device, the cephalad portion of the device comes into close contact with the anterior cortex of the L4 vertebral segment as it passes anteriorly in the L4-5 disc space. Therefore, special care must be exercised in preparing the L4-5 disc space. Specifically, because of the risk of violating the anterior annulus of the L4-5 disc when using the nitinol cutters, injury to the aortic and iliac vessels is possible.

Contraindications

Contraindications include prior surgical intervention or radiation therapy, which results in fibrous adhesions in the presacral space, or a history of significant colitis or perirectal abscess. The procedure depends on opening the presacral space by mobilizing and displacing downward the rectum and retroperitoneal contents, which ordinarily are closely approximated to the periosteum of the anterior sacrum. Prior bladder or cesarean section/hysterectomy is not a contraindication to this procedure unless the presacral space was surgically violated. This presacral approach may be contraindicated for spondylolisthesis that does not spontaneously reduce or cannot be surgically reduced; in these cases, the rod could advance too far posteriorly at L5 and be misdirected into the spinal canal .

Disadvantages for Other Interbody Approaches

Anterior lumbar interbody fusion (ALIF) requires an open exposure, usually with the assistance of a co-surgeon. Difficulty in achieving adequate exposure for performing an ALIF can result from fibrosis of the anterior spine and can be related to the extensive inflammatory response induced by degenerative disc disease or previous posterior surgery. Fibrosis and prior inflammation often result in vascular and bowel injury and retrograde ejaculation. Some patients opt not to undergo an anterior approach because of the abdominal incision and possible risk of large hernia. Despite the extensive experience of surgeons with the ALIF approach, some patients refuse to consider an anterior approach and seek surgeons who can provide other options, such as posterior lumbar interbody fusion (PLIF) or transforaminal lumbar interbody fusions (TLIF). However, both carry greater risks of dural and neurogenic injuries than the transsacral approach. Laparoscopic minimally invasive lumbar fusion has been abandoned because of exposure complications. Additionally, once an anterior approach is complete, the patient must be repositioned; this consumes valuable surgeon and operating room time.

Advantages of the Paracoccygeal Transsacral Approach

Positioning and Access to the Spine

The paracoccygeal transsacral approach gives an advantageous access to the spine from an anterior approach while the patient remains positioned prone for the entire surgery. This permits the posterior decompression/fixation to be performed without adding time or repositioning and redraping the patient. The paracoccygeal approach does not require an exposure surgeon and is completed through a minimally invasive incision. Although the rectum is in the presacral space, there is minimal retraction and postoperative ileus is rare with this technique.

Minimally Invasive

Because of the minimally invasive nature of this approach, the one-level L5-S1 interbody fusion can be successfully completed in the outpatient/ambulatory setting.

Biomechanics

The biomechanical properties of this device have been extensively studied and published. This device offers superior fixation across the L5-S1 segment because of its location across the anterior sacrum, the S1 end plate, the L5 end plate, and into the L5 vertebral segment, extending almost to the top of the L5 end plate. This implant serves as a buttress against the shear forces associated with spondylolisthesis and long-construct fusions. In analyzing sacral screw strain and range of motion in long posterior fusion constructs for deformity, Fleischer and colleagues reported that the AxiaLIF rod reduced strain on the sacral screws better than TLIF and ALIF constructs and was equivalent to other forms of sacral iliac fixation. Other devices (e.g., posteriorly placed interbody cages) are wedged into the interbody space without firm fixation. This lack of firm fixation may cause loss of correction of a spondylolisthesis reduction and posterior expulsion of the interbody cage.

For treatment of spondylolisthesis, its passive reduction is often observed under anesthesia after positioning the patient. If this does not happen, active reduction and realignment in situ can be accomplished in almost all cases by the following technique. First, the presacral access to the L5-S1 disc space is established and the discectomy is performed as described previously. The posterior decompression/facetectomies and placement of pedicle screws are then completed. Many minimally invasive pedicle-screw systems possess robust built-in reduction capabilities; a strong screw bone interface is required. Poor bone density may prevent consideration of aggressive reduction maneuvers. Once the listhesis is reduced/realigned, thus establishing a safe trajectory, the presacral device can be advanced into position (see Fig. 88-3 ). With these techniques, a patient with a grade III or IV spondylolisthesis can undergo successful reduction and fixation.

In 26 patients with symptomatic grades I and II spondylolisthesis who underwent AxiaLIF and percutaneous pedicle screw reduction, Gerszten and associates reported no intraoperative complications, minimal blood loss (range 20 to 150 mL), and 1-day median hospital stay. The spondylolisthesis grade was improved after axial lumbar interbody fusion in 13 (50%) of 26 patients, with a reduction of at least 1 grade. Axial pain severity improved, decreasing from 8.1 ± 1.4 at baseline to 2.8 ± 2.3 after reduction and fusion. Two years postoperatively, all patients showed solid fusion. Some anecdotal cases have shown solid fusion at 6 years ( Fig. 88-4 ). In comparison, the ALIF technique in the treatment of spondylolisthesis cannot leverage the power of pedicle screws to simultaneously reduce the spine in conjunction with an anteriorly placed AxiaLIF rod. This is a key advantage of the paracoccygeal presacral approach.