The approach is especially useful in the case of low-grade spondylolisthesis where an axial construct can reduce the amount of shear transfer across the already compromised posterior ele­ments during normal range of motion. Fleischer et al. [5, 12] performed range of motion testing across a destabilized L5–S1 spondylolytic spon­dylolisthesis cadaveric model using a posterior pedicle screw fixation combined with either a transforaminal or trans-sacral fusion. It showed that a posterior fixation with pedicle screws com­bined with anterior fusion using the trans-sacral approach showed statistically significant reduc­tion in range of motion in flexion, lateral bend­ing, and axial torsion when compared to stand-alone posterior fixation and/or a combina­tion of pedicle screws plus transforaminal lum­bar interbody fusion.

The rate of pseudoarthrosis at the L5–S1 level is directly proportional to the number of levels fused. The trans-sacral approach can be used to decrease nonunion rates in long posteriorly instrumented constructs by providing an anterior load-sharing construct. This decreases the amount of S1 screw strain and increases the sur­face area available for fusion. Fleischer et al. [12] showed that the amount of S1 screw strain was significantly reduced in the pedicle screw plus trans-sacral group versus the pedicle screw plus TLIF group with differences in strain reduction of 50% in extension, 29% in lateral bending, and 24% in axial torsion.

– Lumbosacral pseudoarthrosis (in the absence

Preoperative imaging such as an MRI, flexion/ extension films, and/or CT scan of the lumbosa­cral spine should be available to determine the patient’s suitability for surgery. It is important that these imaging modalities include the tip of the coccyx as a detailed anatomical overview of the pre-sacral area is important to avoid any pos­sible damage to the surrounding neurovascular, abdominopelvic, and urogenital structures. It also helps with assessing the desired trajectory. An MRI allows great visualization of the pre­sacral space. A surgeon is able to preoperatively determine the thickness of the pre-sacral fat pad and visualize any potential areas of pre-sacral scarring and rectal adherence to the sacrum and accurately assess the height of the intended disc space. If there is any suspicion of bowel adher­ence, some authors recommend a preoperative CT scan with rectal contrast to clearly delineate the boundaries of the bowel/rectum and rule out any preexisting perforations [

The blunt dissecting tool is then used to continue the dissection. It is advanced cephalad in a midline trajectory, always keeping the tip engaged on the anterior surface of the sacrum to approximately the S1/S2 junction. We recommend using biplanar flu­oroscopy to maintain a midline trajectory and keep­ing the dissecting tool in the pre-sacral “safe zone.” This is accomplished with “fingertip” control on the handle of the dissecting tool and fluoroscopic guid­ance in both A/P and lateral planes.

Once the proper trajectory is established, the blunt stylet is exchanged for the beveled guide pin (Fig. 31.8). The tip of the bevel must be aligned with the thumbscrew on the handle. The beveled guide pin is then docked into the sacrum by gently tapping it with a mallet. Under A/P and

The next step involves removal of the guide pin handle and attachment of the guide pin exten­sion. This is followed by careful removal of the dissecting tool over the beveled guide pin using the extension attached previously.