Meng et al [3} reported computer navigation versus fluoroscopic guided navigation for thoracic pedicle screw placement utilizing a different CT system—the ISO-C 3D. The incidence of complications such as screw misplacement had a lower incidence in the computer navigated group—10 events out of 290 versus C-arm fluoroscopy 38 events out of 283 (odds ratio = 0.23, p < .001). Their meta-analysis of 14 publications showed a lower insertion time per screw for computer navigation group compared to the conventional navigated group. The ISO-C 3D can be thought of as a first generational robotic computer navigated system which often required multiple re-registrations, therefore the operative time, estimated blood loss and other secondary outcomes were not significantly improved.
During surgery it is very common for less experienced roboticists to “gently” expose the pedicle screw’s starting position. Unfortunately by retracting the paraspinal muscles even with seemingly little force, the pedicle screw insertion can be misdirected by as much as a centimeter. While this happens in the real situation, at the same time the robotic navigation screen can indicate a perfect screw placement position. However we have found with using the E3D this can be prevented by percutaneous or stab incisional placement of screws. The screws are placed through the paraspinal muscles instead of retracting the paraspinal muscles and inadvertently moving the vertebral target. Then an intraoperative image can be obtained, essentially rebooting or reconfiguring the virtual spine to the actual spine anatomy in near “real time” (approximately 45 seconds prior to screw placement).
The E3D imaging platform is three in one—Cone-Beam CT (CBCT), fluoroscopy, and digital radiography (DR). The application to spinal deformity, T4 to L1 or T10 to pelvis provides a more global visualization for the surgeon, 236mm along the spine —50% larger field of view compared to legacy systems (Fig. 3 and Fig. 4).
The E3D has two C-shaped gantries, inner and outer, which allow the x-ray beam to rotate a full 360-degree when used during CBCT. The inner and outer C-shaped gantries can also be nested together to allow the E3D to be position in a lateral position, same as a typical C-arm workflow. This allows the surgeon to fine tune the instrumentation and work around the E3D without moving it in and out away from the operating table (Fig. 5).
The tertiary nature of our deformity cases included 30 per cent revision cases with prior instrumentation—it is critical that the E3D allows for automatic subtraction of the prior metal implants and reduces metal scatter and artifact. We have used other intraoperative imaging systems that provide a good axial image except that the visualization of the spinal canal is totally lost as soon as a pedicle screw is inserted. In a residency training program this negates the advantage of an intraoperative CT—it is mandatory to be able to confirm/reevaluate screw position relative to the canal. Figure 2 shows a case with an intracanal screw placed by robot at Elsewhere General. Even a resident with limited experience could prevent this complication with E3D because the visual resolution of the spinal canal is unmistakable.
It is important to mention several limitations of our study. First, it was not possible to separate out either in the operating room record or the radiation records the amount of time utilized during surgery for the spine anatomy registration– this had to be indirectly measured from the total duration of surgery. Second, the two groups overlapped temporally so one might argue that the “learning curve” of robotics more directly influenced the robot only group. However there were two additional surgeons who adopted robotics primarily in the E3D group therefore essentially two surgeons learning curves comprised the Group 1 complications and two additional surgeon’s learning curves were included in the Group 2 experience. Furthermore the learning curve of adopting the new technology of intraoperative scanning and work flow was only present in the E3D Group. So this would serve to bias the results against Group 1, the E3D group, which in fact had only three of 80 cases require a return to the operating room for any reason (versus 11 of 80 patients for Group 2).
In our experience with 80 consecutive cases, the more unstable the spine, the more important it is to obtain the virtual construct based on intraoperative position—prone, without paraspinal muscle retraction, without respiratory excursion, after paraspinal dissection is completed, and without dynamic reference base (DRB) movement. In short, the more unstable the spine, the greater the advantage of E3D.