Trans-sacral Approach

William D. Tobler

Abstract

This chapter highlights the features of this distinctive surgical approach (trans-sacral approach) for lumbar fusion. Its anatomic corridor in the presacral space provides a unique access to the spine. The surgeon prepares the disc space with looped/flat cutters using fluoroscopic guidance and the biomechanics for the fixation device use a novel large threaded rod for one- or two-level fusions. Initially, some of these unique features became a barrier to its adoption, and publicized complications led to concerns about overall safety. Subsequently, refinements in patient selection and technique strategies achieved satisfactory outcomes. The trans-sacral fusion is minimally invasive, offering a sound option for select patients who have degenerative disc disease, multiple recurrent disc herniations, or spondylolisthesis. The chapter details its benefits (e.g., patient prone requires no repositioning, no access surgeon needed, preservation of muscles or supporting ligaments, superior stabilization, suitable for obese patients) and disadvantages (e.g., unrecognized bowel perforation, interspace distraction, and lordosis). A well-illustrated step-by-step guide leads the reader with tips for patient selection, preoperative imaging and examination, surgical technique from incision to closure, and complication management. Case examples discuss the principles for successful presacral interbody lumbar fusion. With specialized training, this presacral technique should be an option for surgeons dedicated to minimally invasive spine fusion.

Keywords: lumbar interbody fusion, AxiaLIF, presacral approach, minimally invasive fusion, surgical technique, patient selection, two-level presacral approach

41.1 Introduction

The trans-sacral (or presacral) approach is a minimally invasive surgical technique to achieve lumbar interbody fusion at L5–S1, or both L4–L5 and L5–S1. Using the unique trans-sacral access to the L5–S1 disc, the surgeon crosses through the space anterior to the sacrum, starting distally at the tip of the coccyx, and enters the sacrum at the S1–S2 junction to access the interspace in an axial plane ( Fig. 41.1). This new operation was introduced as a one-level device in 2005 with Food and Drug Administration clearance for use at L5–S1.¹^,² Its initial FDA clearance also required stabilization posteriorly with facet or pedicle screws; clearance has not yet been obtained for the two-level device.

This new trans-sacral operation introduced features distinct from any other interbody surgical approach. First, the anatomic corridor in the presacral space provides access to the spine previously not used for interbody fusion.³^,⁴^,⁵ Second, the methodology of interspace preparation uses looped/flat cutters to remove the disc, without direct visualization of the interbody space by the surgeon ( Fig. 41.2). Third, the biomechanics of the fixation device itself are unique: this large threaded rod crosses through the disc space oriented vertically aligned with the axis of the spine, starting at the sacral interface and extending across L5–S1 into L5. In cases of a two-level fusion, a longer device also crosses the L4–L5 interspace, extending up to the L4 vertebra.

Some of these unique features of the presacral approach at times became a barrier to its adoption. The technique was unfamiliar to surgeons, and publicized complications led to concerns about its overall safety.⁶^,⁷^,⁸ Fusion outcomes have been controversial, perhaps not well understood, or sometimes studied inadequately. Several studies reporting poor outcomes fueled apprehensions about the approach itself (especially the two-level technique) when, in fact, these outcomes were possibly related to poor surgical technique.⁹^,¹⁰ Subsequently, others refined patient selection and technique strategies, and satisfactory outcomes after the presacral two-level fusion also followed.³^,¹¹^,¹²^,¹³

Fig. 41.1 Axial lumbar interbody fusion (AxiaLIF) corridor of approach. (a) Approach begins adjacent to the coccyx, moves midline along the avascular sacrum through the presacral fat to access the sacral promontory, and continues trans-sacral through bone to the L5–S1 disc space. (b) Titanium rod is composed of three parts: the S1 segment, inner distraction collar, and tapered L5 segment. When inserted, the distraction rod is adjusted to restore the height of the disc space and indirectly decompresses the neural foramen. (c) Facet screws inserted percutaneously achieve a 360°-stabilization of the motion segment. (Reproduced with permission of Mayfield Clinic.)

Fig. 41.2 (a) Loop cutters to debulk nucleus and lightly abrade end plates. (b) Brushes to evacuate the disc material. (c) Flat cutters designed to debulk nucleus in tight disc spaces (< 2.5 mm). (d) End plate rasps to lightly abrade end plates. (Reproduced with permission of Quandary Medical.)

41.1.1 Advantages

The presacral technique provides unique benefits and advantages compared with other traditional methods of lumbar fusion at L5–S1. First, its anterior approach to the interbody at L5–S1 gives access to the disc space anterior to the sacrum and is achievable with the patient positioned prone. This is an advantage when compared with the typical anterior lumbar interbody fusion (ALIF) with its transabdominal approach to L5–S1. Unlike the two-stage positioning for the ALIF (i.e., supine for the initial part of the procedure and repositioned prone for posterior stabilization), the presacral approach requires no repositioning.

Second, unlike the typical ALIF, no access surgeon is needed for the presacral approach. Third, in contrast with the opening and retraction of the abdominal wall musculature for ALIF, no muscles or supporting ligaments are divided with the presacral approach. Unlike the traditional transforaminal lumbar interbody fusion (TLIF) or posterior lumbar interbody fusion (PLIF) approaches, the surgeon performing a presacral approach does not disturb, manipulate, or retract the dural sac or the exiting and traversing nerve roots when preparing the disc space and inserting the interbody fixation device.¹⁴

The biomechanics of the presacral device offer advantages of initial superior stabilization over other techniques using interbody devices. Patients with a spondylolisthesis and high pelvic incidence face a high risk of construct failure because of the strong shear-force vector acting against the fixation of spinal fusion; most interbody devices are wedged into the disc space and do not provide resistance against such forces.¹⁵^,¹⁶^,¹⁷

Finally, the presacral fusion technique can be suitable for obese patients; this is unlike the greater technical challenges of exposing the spine during anterior or posterior approaches when division through deep layers of soft tissues is needed. With higher obesity, these surgical procedures (ALIF and TLIF) become increasingly difficult and thus pose higher risks for patients, whereas the presacral approach does not. Rather, the distance from the tip of the coccyx/entry point to the L5–S1 disc space does not adversely change in obese patients. In fact, the procedure can actually be easier to perform in overweight patients who were not candidates to undergo other traditional approaches. For example, obese patients typically have a large presacral fat pad, which makes access safer because the rectum is not too close to the sacrum.

41.1.2 Disadvantages

Concerns about protecting the rectum have been the perceived disadvantages of the procedure. However, careful technique and evaluation of the rectum before and after the presacral approach have reduced the risk of unrecognized bowel perforation to very low rates.⁶^,⁸^,¹⁸ Another potential disadvantage of the device concerns interspace distraction and lordosis. The original device was engineered with the capability to distract the interspace when inserted. Differential thread counts on the L5 and S1 segments of the rod utilized a reverse Herbert method. The distracting force of the threaded device required a strong bone–device interface that often failed, especially in patients with osteopenia, leading to subsidence and failure to maintain distraction. Creation of lordosis is possible with the presacral device, but not predictable. Therefore, the presacral approach should not be used in a patient with significant positive sagittal balance that requires interbody fusion and significant restoration of lordosis at L5–S1.

41.1.3 Evolution of the Technique

The second-generation presacral device incorporated improvements that resolved the stresses placed on the vertebral end plates imposed by the original design’s reverse Herbert technique. This newer modular design consists of L5 and S1 segments and an inner threaded collar that are assembled before insertion (see Fig. 41.1). Distraction of the interspace occurs after the device is advanced and positioned across the disc space. A torque rod is inserted into the second-generation device, and the inner collar is maximally extended to distract the space. With additional refinement, the upper end of the device is now tapered. Application of a porous bead coating has improved fixation and promoted arthrodesis. Introducing these changes subsequently eliminated the radiographic halo effect seen around the upper end of the L5 rod, which was often mistaken on X-ray and CT imaging for loosening of the device or pseudarthrosis.

A presacral access kit was introduced to protect the bowel. This inflatable, soft plastic mattress can be advanced into the presacral space and inflated with saline to create a barrier between the instrumentation and retroperitoneal contents during the procedure ( Fig. 41.3). A soft rubber gasket is added to the tip of the exchange cannula; this large-diameter tube is required to advance the device into the spine. The rubber gasket forms a soft seal at the distal sacrum; fixed with two small Steinmann pins, it stabilizes the exchange cannula during device insertion and prevents any soft tissue (e.g., rectum) from becoming entrapped inside it.

Evaluation of the bowel integrity is encouraged before and after the approach. Injecting air into the bowel before the procedure locates the position of the rectum in the surgical position. After the procedure, saline can be injected and aspirated from the rectum; any blood found in the aspirate raises a concern for a bowel perforation. Injected contrast into the rectum at the close of the procedure can demonstrate a fistula. Finally, a rigid scope can be inserted in the rectum to directly inspect the rectal wall. These various options, in conjunction with meticulous surgical technique, can reduce the incidence of bowel perforation to less than 1%.¹⁸ Intraoperative identification and immediate repair of a perforation can prevent infection and eliminate the need for colostomy.

Fig. 41.3 Presacral access. (a) Begins with blunt dissection to free Waldeyer’s fascia. (b) Presacral access kit is inserted against the sacral surface. Inflation with saline forms a mattress-like device to deflect soft tissues away from the sacrum, making a protective barrier between the bowel and instruments. Fluoroscopic image shows the deployed protective access kit. (Reproduced with permission of Quandary Medical.)

41.2 Indications and Contraindications

This surgical procedure is indicated for a lumbar fusion at L5–S1 or L4–L5 and L5–S1, typically in skeletally mature patients who have degenerative disc disease, multiple recurrent disc herniations, or spondylolisthesis. The classic course is at least 6 to 12 months of symptoms that fail to respond to or be managed by therapy, anti-inflammatory agents and injection therapy, and lifestyle modification. Most patients who have undergone hysterectomies or bladder or other abdominal surgeries that do not violate the presacral space can also undergo the presacral approach.

Contraindications include significant scarring in the presacral space that makes mobilization of the rectum and soft tissues impossible. Other contraindications are after surgical intervention or radiotherapy in the presacral space, and in cases of significant inflammatory bowel disease.⁶^,¹⁹

41.3 Preoperative planning

41.3.1 Patient Selection

Potential candidates for interbody fusion at L5–S1 or L4–L5 and L5–S1 can be evaluated for the presacral approach. When the usual conservative measures fail, MRIs of the lumbar spine and pelvis as well as standing lateral/flexion–extension X-rays are routinely obtained. Bone density studies are important for patients at risk of osteoporosis. However, dual energy X-ray absorptiometry (DEXA) scan results do not always correlate with the hardness of the shell of the bone, which is necessary for fixation of the implant. As in any surgical planning, medical evaluation will identify any other medical contraindications to a surgical procedure.

Patient Profiles

Ideal candidates for a presacral fusion have a modest build, low pelvic incidence, and a classic-shaped sacrum. In patients with degenerative disc disease undergoing the presacral fusion, Modic end plate changes without spondylolisthesis represent the best case for good outcomes and minimal technical challenges. Although grade I or II spondylolisthesis is a more difficult scenario, patients can usually achieve excellent technical results. However, a grade III or higher spondylolisthesis is far more difficult; the procedure is only recommended if the slip can be reduced intraoperatively to obtain the required alignment and trajectory before final placement of the presacral device. This can be accomplished in most cases with posterior osteotomies and the powerful reduction capabilities of most pedicle screw systems. With the patient positioned prone, the surgeon can simultaneously perform portions of the presacral procedure and the posterior portion to achieve reduction of the spine.

The presacral approach may be contraindicated for spondylolisthesis that does not spontaneously reduce or cannot be surgically reduced; in these cases, the rod would advance too posteriorly at L5 and could be misdirected into the spinal canal ( Fig. 41.4d).

41.3.2 Physical Examination

There are no special aspects during the patient’s physical examination before a presacral fusion. Complete musculoskeletal and neurological examinations are required. Gait observation is extremely important to evaluate sagittal balance. Of note, 1 week before the procedure, patients should discontinue all nonsteroidal anti-inflammatory drugs (NSAIDs), antiplatelet agents, minerals, and vitamin supplements.