8.1 Introduction

As spinal surgeons continue to strive for increasingly minimally invasive surgical techniques for various spinal interventions, a trend toward reliance on various intraoperative image-guidance systems to aid in achieving minimal access goals has developed. ¹ Such systems include traditional fluoroscopy, computer-assisted navigation (CAN), and various robotic platforms. However, the cumulative ionizing radiation dose to spinal surgeons secondary to this increasing reliance on intraoperative fluoroscopy has also become an area of significant interest and research, as there may be an increased risk of certain types of malignancies to spinal surgeons related to this lifetime exposure. ^{2 ,​ 3} Strategies to mitigate, or at least reduce, the cumulative radiation exposure have begun to gain widespread traction in the spine surgery community, and advances in navigation and robotics may have some theoretical advantages in this regard.

Since the first pedicle screw was implanted via CAN in 1995, three-dimensional navigation and robotic systems continue to transform the landscape of spine surgery. ^{4 ,​ 5 ,​ 6} These systems have been shown to improve pedicle screw accuracy throughout the literature. ^{7 ,​ 8 ,​ 9 ,​ 10} There is also an increasing awareness of the impact these systems may have on radiation exposure to the patient, surgeon, and operating room team. ¹¹ Some studies have attempted to examine the radiation dose to individual patients with regard to the use of navigation, as there is some concern regarding additional preoperative or intraoperative computed tomography (CT). ¹² Hypothetically, however, CAN may decrease or altogether obviate the necessity of intraoperative fluoroscopy, thereby reducing surgeon exposure to radiation, particularly when compared to traditional fluoroscopic image guidance. The benefits to the surgeon and operating room team must be considered in the context of potential risks to the patient, and vice versa. In this chapter, studies evaluating the effects of various CAN and robotic platforms on radiation exposure to the patient, surgeon, and operating room team will be explored. However, it is important to clearly note that the literature directly comparing radiation exposure to patients and surgical teams in navigated and nonnavigated spinal instrumentation cohorts is relatively limited, and major recommendations have not yet been established.

8.2 Patient Exposure

Many studies, including a relatively recent meta-analysis, have demonstrated the precision and accuracy with which pedicle screws can be placed with CAN. ^{13 ,​ 14 ,​ 15} In addition, other spinal procedures such as vertebral body augmentation for fractures ¹ or intradiscal electrothermal treatments ¹⁶ can also be performed with the use of navigation. While no obvious clinical benefit has been demonstrated with regard to more accurate pedicle screw placement, ¹⁷ concerns have been raised with regard to potentially increased radiation exposure to the patient secondary to either pre- or intraoperative CT scan. ¹²

Mendelsohn et al ¹⁸ performed a retrospective cohort study examining CAN versus fluoroscopic-guided pedicle screw instrumentation. The authors found that for 73 patients in the CAN group, “intraoperative CT-based navigation increased the radiation dose emitted to the patient by 2.77 times compared with conventional fluoroscopy-guided cases.” However, the authors note that the cumulative dose to the patient intraoperatively was less than a traditional CT scan, such as would be obtained for preoperative CAN systems. In contrast, Urbanski et al ¹⁹ compared traditional freehand pedicle screw placement versus placement with intraoperative 3D navigation in patients with idiopathic scoliosis and assessed the radiation dose received by patients with both techniques. The authors found no difference in accuracy between techniques in 49 consecutive patients, though the only pedicle breaches greater than 4 mm occurred in the upper thoracic spine in the freehand group. Most alarming, however, was their finding that patients undergoing CAN pedicle screws received almost 700 mGy/cm more than the freehand group, which was statistically significant.

In contrast, however, Villard et al ¹¹ conducted a randomized prospective trial of CAN versus fluoroscopy-guided pedicle screw placement in 21 patients undergoing lower thoracic and/or transforaminal lumbar interbody fusion (TLIF) to determine patient radiation exposure risk. They identified instances of radiation exposure occurring at several different points during the navigated procedures, namely (1) when marking the spinal level initially; (2) positioning of the C-arm after exposure prior to running the 3D scan; (3) implantation of the interbody devices; and (4) final 3D images to confirm screw position prior to wound closure. Cumulative radiation dose to the patient was obtained from the imaging system and was found to be reduced in the navigated group (888 vs 1,884 cGy/cm², respectively), though this finding did not reach statistical significance. The authors concluded that despite failing to show any statistically significant reduction in patient radiation exposure, the trend toward decreased total dose should be considered. Further corroborating these findings in a comparative cohort study, Fomekong et al ²⁰ found that the radiation exposure to patients undergoing percutaneous pedicle screw implantation was significantly reduced with intraoperative three-dimensional fluoroscopy: the average radiation dose per patient was 571.9 mGy/m2 in the nonnavigated group, compared with 365.6 mGy/m2 in the navigated group. Zhang et al ²¹ had similar findings when using intraoperative CT-based navigation during lateral interbody fusion: radiation exposure to the patient was significantly lower in the intraoperative CT scan group compared to the conventional fluoroscopy group (9.38 vs. 44.59 mGy, respectively).

In a study examining patient radiation exposure during navigated vertebral body augmentation with kyphoplasty or vertebroplasty, Barzilay et al ¹ reported that the use of robotic assistance initially increased radiation exposure to the patient by the nature of the requirements for high-kV preoperative CT scan; however, they were able to alter the preoperative protocol and reduce the preoperative dose to the patient by 75%. When compared to the published literature on navigated vertebral augmentation, they found a reduction of over 50% in radiation exposure with the use of surgical robotics. However, they noted that in patients with osteoporosis, a higher power preoperative CT scan may be required to successfully navigate such procedures. ¹ Based on this study, it may be likely that the tradeoff for decreased intraoperative radiation exposure may increase preoperative exposure, but may vary from patient to patient. A systematic review examining this question concludes that the use of intraoperative CT to facilitate CAN results in increased radiation exposure to the patient, specifically when compared with standard fluoroscopy, but the authors found that in general it is a lower dose than preoperative CT. ²²