Chapter 7: Interspinous fusion with lateral percutaneous technique

Michael Gyorfi, Steven M. Falowski, Alaa Abd-Elsayed

Introduction

The lateral percutaneous technique is a minimally invasive approach to interspinous-interlaminar fusion with a device used to stabilize the thoracic, lumbar, and sacral spine. It is intended for usage with bone graft material placed into the device and is designed for connection to the posterior noncervical spine at the spinous processes in the interspinous space through its bilateral locking plates. This lateral minimally invasive surgery (MIS) technique is performed under fluoroscopy. A wide variety of sizes allows for improved anatomic fit, and the core threaded post provides regulated distraction.

Indications

The intended use of the lateral percutaneous technique is with a posterior, nonpedicle supplemental fixation device at a single level in the noncervical spine. It is designed to fixate/attach plates to spinous processes to achieve supplementary fusion within the interspinous space. The most common indications are degenerative disc disease (DDD), spondylolisthesis, and spinal trauma.¹

Patient selection

Proper patient selection may greatly affect the efficacy. Smoking has been shown to increase the incidence of nonunion. These patients should be encouraged to stop smoking and be made aware of the increased risk. Patients who are alcoholic, malnourished, or obese are also at an elevated risk for complications. Lastly, osteoporosis may make patients more prone to poorer outcomes and complications such as spinous process fractures.

Step by step description of the procedure

1. Preoperative planning is the first step. Routine preoperative tests include anteroposterior (AP) and lateral x-rays (flexion and extension views are also indicated), magnetic resonance imaging (MRI), and/or computed tomography (CT) myelography. Gross instability, severe spondylolisthesis, major scoliosis, severe osteoporosis, and ankylosed spinal section must all be ruled out. A preoperative CT is advised if the lateral MIS approach is necessary at L3–L4 or above, to ensure a safe trajectory.
2. The patient should be positioned in a prone posture on a frame that reduces lordosis and prevents the abdomen from being squeezed. Tilting the pelvis by inclining the table at the level of the pelvis is recommended. The result will be that the spinous processes are naturally distracted. In both the AP and lateral planes, the frame and operating table must be radiolucent. The lateral decubitus position may be used as an alternative patient position (Fig. 7.1).
3. Identify the midline of the spinous processes at the level to be instrumented using manual palpation and AP fluoroscopy and insert a spinal needle. Define anatomic landmarks and transfer them onto the skin using lateral fluoroscopy. The superior margin of the inferior spinous process is marked by a skin mark (Fig. 7.2; seen in blue). The inferior border of the superior spinous process is marked by a second skin mark (shown in magenta). The posterior boundary of the facet joint is marked with a third skin mark (shown in orange). Make a 2.5-cm longitudinal incision between the blue and magenta lines and along the orange line (Fig. 7.2).
4. Insert the guidewire into the aiming device until the first stop is reached. The guidewire is introduced through the incision. The guidewire should be put as far anterior as feasible for best results. Increase the guidewire length by depressing the aiming device knob. Carefully move the guidewire between the spinous processes and puncture the interspinous ligament under lateral fluoroscopy (Fig. 7.3).
5. Advance the guidewire about 2 cm across the midline of the spine under AP fluoroscopy. With AP and lateral views, double-check the location of the guidewire (Fig. 7.4).
6. Remove the aiming device from the guidewire by depressing the aiming device knob. It is critical to keep the guidewire in place. Thread the guidewire extension onto the guidewire. While inserting dilators, sleeves, and other devices, the guidewire extension assists in maintaining proper guidewire placement (Fig. 7.5).
7. Over the guidewire, slide the 3-mm soft tissue dilator. The 3-mm dilator is introduced through the skin incision while holding the guidewire in place under AP fluoroscopy. Rotate and advance the 3-mm dilator until it is near to the spinous processes. Optional: If facet hypertrophy prevents the sleeve from docking against the spinous processes, the bone rasp can be placed over the guidewire and turned clockwise to progressively diminish the facets’ bulk. Leave the guidewire in place while removing the bone rasp. Optional: If the soft tissue rasp is unable to proceed between the spinous processes because it is in contact with them, the starter rasp can be put over the guidewire and spun clockwise to gradually divert the spinous processes (Fig. 7.6).
8. The soft tissue rasp is introduced into the interspinous process space over the guidewire. The interspinous ligament is partially removed, and the spinous processes are partially decorticated by rotating the rasp clockwise. After that, the rasp is removed, but the guidewire is left in place (Fig. 7.7).
9. Over the extended guidewire, the graduated tap is inserted. The tap is inserted clockwise into the interspinous process space under AP fluoroscopy. Engage the threads of the tap with the spinous processes with moderate effort. The spinous processes are increasingly distracted as the tap is progressed. The degree of distraction may be evaluated by looking at which tap size hole is positioned between the spinous processes once enough distraction has been achieved. The optimum implant size is determined by the degree of distraction. Leave the graduated tap in place when putting the implant onto the G2-inserter to preserve the appropriate route for implant placement (Fig. 7.8).
10. The tap includes sizing holes that correlate to the degree of distraction, and these holes may be seen on AP fluoroscopy to estimate the implant size. The 23-mm sleeve should be slid over the 20-mm sleeve. The 23-mm sleeve should be inserted until it is close to the spinous processes. For the 26-mm sleeve, repeat the process. Remove the 20-mm and 23-mm sleeves but keep the 26-mm sleeve (Fig. 7.9).
11. Remove the guidewire while leaving the sleeve in place against the lateral surface of the spinous processes. Attach the relevant size insertion adapter to the distal end of the inserter after determining the appropriate size. The insertion adapter will be the same color as the hex nut of the same size (Fig. 7.10).
12. To attach the device, make sure the inserter is unlocked. The position indicator should be aligned with the arrowhead (Fig. 7.11).
13. The spring-loaded adapter shaft is first squeezed against the fixed plate knob until it bottoms out, then turned counterclockwise for about one-eighth of a full turn (Fig. 7.12).
14. Snap the implant into place by aligning the extension plate in the same orientation as the laser engraving. The extension plate can be aligned with the plate reference lines with proper positioning (Fig. 7.13).
15. Rotate the plunger knob clockwise until the position indicator is in the locked position to secure the device to the inserter. The device is automatically locked to the inserter when the plunger stop clicks to the right (Fig. 7.14).
16. Hold the fixed plate knob and (1) spin the adaptor shaft clockwise about one-eighth of a turn, and (2) gently spring forward the adaptor shaft. The hex nut will be engaged by the insertion adaptor. Slowly twist the adaptor shaft until the insertion adaptor slips into position if it does not correctly contact the hex nut (Fig. 7.15).
17. Bone graft material is introduced by threading bone graft material into the threaded body while holding one wing open and the other closed. The devices external threads are likewise covered with bone graft material (Fig. 7.16).
18. The inserter is inserted into the sleeve with the device connected and progresses to the interspinous process area, aiming as far anterior as feasible. To engage the threads, rotate the inserter clockwise. The device is moved into the interspinous space under fluoroscopy until the fixed plate reaches the spinous processes (Fig. 7.17).
19. To use the extension plate, first slide and hold the plunger stop to the left, then turn the plunger knob clockwise until it stops. The plate deployment symbol will be near to the position indicator (Fig. 7.18).
20. Ensure that the extension plate has been deployed and will contact the spinous processes as far anterior as feasible during fixation using fluoroscopy. The device may now be attached to the spinous processes (Fig. 7.19).
21. To secure the implant to the spinous processes, hold the inserter in place and advance the fixed plate by rotating the fixed plate knob clockwise. The extension plate will be brought to contact the distal lateral surface of the spinous processes as the fixed plate is tightened (Fig. 7.20).
22. A ratcheting sensation will be felt, which represents the implant’s locking mechanism. The amount of torque used should be proportional to the patient’s bone quality. Check the plate reference lines on the inserter to ensure appropriate extension plate alignment during fixation (Fig. 7.21).
23. Twist the plunger knob counterclockwise until the position indicator reaches the locked position. The plunger stop moves to the right automatically (Fig. 7.22).
24. To detach the removable body from the implant, gently pull the inserter laterally. The inserter is taken out of the patient’s body (Fig. 7.23).
25. Slide and hold the plunger stop back to the left once outside the patient’s body, then spin the plunger knob counterclockwise until it stops. The inserter’s removable body is now detachable (Fig. 7.24).
26. The sleeve is taken off. Sutures or Steri-Strips are then used to close the wound (Fig. 7.25).