Success Rates and Time: Can Three-Dimensional Navigational Imaging Improve the Success and Time Required for Minimally Invasive Surgery and Minimize Radiation Exposure to Those in the OR Suite?

24 Success Rates and Time: Can Three-Dimensional Navigational Imaging Improve the Success and Time Required for Minimally Invasive Surgery and Minimize Radiation Exposure to Those in the OR Suite?

Eric W. Nottmeier

24.1 Introduction

Image-guided spinal surgery was introduced in the mid-1990s.1,2,3,4 Image guidance technology allows the surgeon to navigate the patient’s anatomy on preoperative or intraoperative images by tracking surgical instruments in three-dimensional (3D) space using infrared light. Given the reported 14 to 55% misplacement rate for pedicle screws using standard insertion techniques,^5,6,7,8 along with neurologic injury rates that can approach 7%,⁹ the desire to develop techniques for more precise spinal instrumentation placement helped advance the evolution of spinal image guidance. Accordingly, over the past two decades this technology has progressed, making it more user-friendly and efficient for the spine surgeon. A significant step forward in this process was the introduction of cone beam computed tomography (CBCT) registration for spinal image guidance. During CBCT acquisition, multiple fluoroscopic images are obtained while the device rotates around the patient. These images are then reconstructed into a 3D data set, basically a CT scan, which can then be navigated after these data are transferred to the image-guided system. Advantages of 3D CBCT image guidance include the ability to register multiple vertebral segments at a time without the need to expose the bony dorsal elements, which has made a presence in minimally invasive spinal surgery procedures. This chapter reviews the spinal image guidance literature. Though the use of image guidance is increasing in spinal surgery, this technology is still not used by a majority of spine surgeons. Subsequently, a large part of the literature concerning spinal image guidance describes its use in open procedures, with a smaller part of the literature reporting on minimally invasive procedures.

24.2 The Accuracy of Spinal Image Guidance

Spinal image guidance has been used as an adjunct for instrumentation placement from the ileum to the occiput.10,11,12,13,14,15,16,17,18 Kosmopoulos and Schizas¹⁹ reported their meta-analysis of the spinal image guidance literature and found a median accuracy of 90.3% in 12,299 pedicle screws placed in vivo without navigation versus a median accuracy of 95.2% in 3,059 pedicle screws placed in vivo with navigation. Verma et al²⁰ reported a 93.3% accuracy rate in 3,555 pedicle screws placed using navigation versus an 84.7% accuracy rate in 2,437 pedicle screws placed without navigation in their meta-analysis of the spinal image guidance literature. In another meta-analysis by Tian et al,²¹ pedicle screw insertion accuracy between conventional methods of pedicle screw placement and three methods of spinal image guidance (3D point matching image guidance, 2D image guidance, and 3D CBCT image guidance) was compared. They concluded that higher pedicle screw insertion accuracy occurred when image guidance was used and that 3D CBCT image guidance was the most accurate image guidance technique. Shin et al²² performed a meta-analysis of the literature comparing image-guided pedicle screw insertion to nonnavigated techniques. Twenty studies were included in this meta-analysis which included a total of 8,539 screws (4,814 navigated and 3,725 nonnavigated). A 6% breach rate was noted in the navigated screws as compared to a 15% breach rate in the non-navigated screws. Additionally, no neurologic complications were found in the navigated group, whereas three neurologic complications were noted in the nonnavigated group.

Four randomized clinical trials comparing image guidance to conventional techniques of pedicle screw placement have reported better screw placement accuracy with image guidance.^23,24,25,26 Rajasekaran et al²³ assessed the accuracy of thoracic pedicle screws placed in spinal deformity cases using either fluoroscopic assistance or 3D CBCT image guidance and reported a 2% breach rate in the 3D CBCT image guidance group versus a 23% breach rate in the fluoroscopic group. In a randomized trial comparing screws placed with the freehand technique to screws placed using 3D point matching image guidance, Laine et al²⁴ reported a breach rate of 13.4 and 4.6%, respectively. Randomized studies by Wu et al²⁵ and Yu et al²⁶ reported significantly higher accuracy in pedicle screws placed using 3D CBCT image guidance as compared to screws placed using fluoroscopic guidance. One randomized study has not demonstrated the advantage of spinal image guidance in which Li et al²⁷ reported no significant difference in breach rate in pedicle screws placed using the freehand technique versus pedicle screws placed using 3D point matching image guidance.

24.3 Radiation Exposure with Spinal Image Guidance

Fluoroscopy is frequently used to assist in spinal instrumentation placement. The amount of fluoroscopy time required to place a pedicle screw in open procedures ranges in the literature from 3.4 to 66 seconds per screw.28,29,30,31,32 The use of fluoroscopy requires the surgeon to wear a lead apron and to move around the device during instrumentation placement.³³ Also, a 10- to 12-fold increase in surgeon radiation exposure can occur when fluoroscopy is used for spinal instrumentation cases when compared to nonspinal cases in which fluoroscopy is used.³⁴ In a prospective study measuring surgeon radiation exposure in 24 patients undergoing one- and two-level minimally invasive transforaminal lumbar interbody fusion (TLIF), Bindal et al³⁵ reported that the mean fluoroscopy time per case was 1.69 minutes and the mean radiation exposure per case to the surgeon’s torso (under a lead apron) was 27 mrem. It was concluded in this study that a surgeon could exceed the recommended maximum annual radiation exposure of 5 rem to the torso if he/she performed more than 194 of these procedures annually.

When comparing image-guided pedicle screw placement to pedicle screw placement using fluoroscopy, several in vitro studies have reported less surgeon radiation exposure with the use of image guidance.28,31,33,36 In an in vivo study assessing instrumentation placement in cases of less invasive correction for adult degenerative scoliosis, Scheufler et al³⁷ reported no surgeon radiation exposure using intraoperative CT image guidance. Another in vivo study by Nottmeier et al³⁸ reported no surgeon radiation exposure in 25 consecutive spinal surgery cases using CBCT image guidance. Izadpanah et al³⁹ reported significantly lower radiation time and patient radiation exposure in patients undergoing CBCT image-guided kyphoplasty, as compared to patients undergoing fluoroscopically assisted kyphoplasty. Obviously, no surgeon radiation exposure occurs with the use of image guidance as compared to fluoroscopic techniques because active fluoroscopy is not used during instrumentation placement. The patient’s spine has to be registered using the CBCT device; however, during acquisition of these images, the surgeon and operating room (OR) staff can stand back from the operative field, which limits or eliminates their radiation exposure. Nottmeier et al⁴⁰ measured radiation scatter during intraoperative CBCT registration in 25 spinal surgery cases and determined that radiation exposure to the surgeon and OR staff was minimal if standing at least six feet from the CBCT device. Despite that, it was still emphasized in that study that the surgeon and OR staff should shield themselves during CBCT acquisition or should leave the room. However, radiation exposure to the patient still occurs in 3D CBCT image-guided spinal surgery cases during CBCT registration. Though radiation exposure to the patient must be considered, it should be emphasized that the surgeon and the OR staff will be participating in multiple fusion procedures per year, and the patient will hopefully be undergoing one fusion procedure during that time period. Furthermore, Zhang et al⁴¹ reported that the patient radiation dose delivered by O-ARM (Medtronic) was approximately half of that delivered by a 64-slice CT scanner.

24.4 The Operating Room Time and Learning Curve in Spinal Image Guidance

Though a multitude of authors describe increased accuracy of spinal instrumentation placement with the use of image guidance as compared to standard techniques,9,23,24,25,26,42,43,44 some authors have reported no benefit when using this technology.²⁷ Spinal image guidance is an aid to spinal instrumentation placement and not a substitute for knowledge of the spinal anatomy. Additionally, as with all new technologies and methods, a skill set needs to be developed by the surgeon to successfully apply image guidance to spinal surgery procedures. Learning curves are well documented with new technology in other surgical fields, including laparoscopic and robotic surgery.^45,46

Spinal image guidance technology has been demonstrated to be highly accurate in vitro^47,48; so, it is the in vivo application by surgeons that determines its success in the clinical setting. Learning curves have been described with the use of spinal image guidance.^49,50,51,52 When assessing the OR time associated with spinal image guidance, both increased OR time^{24,27,42,53,54,55} and decreased OR time^23,25,52,56 have been reported. Several steps have to be performed during registration when using 3D CBCT image guidance (reference arc application, draping and undraping the patient, CBCT device positioning, performing the CBCT spin, and data transfer), and the reported time required to accomplish this ranges from 6.5 to 8.5 minutes.^40,57 The relationship between image guidance and OR time is partly dependent on the efficiency of the surgeon and OR staff in accomplishing these steps. Subsequently, studies that report the OR time added or saved in spinal image guidance cases may not be assessing the technology itself, but the OR team’s efficiency in applying this technology. As surgeons overcome the learning curve and gain experience with this technology, OR times can decrease. When assessing the use of spinal image guidance versus standard techniques, Sasso and Garrido⁵² and Johnson et al⁵⁶ found a decrease in OR time with the use of image guidance. Additionally, the authors noted in their studies that OR times decreased as the surgeon became more experienced with image guidance. When compared to traditional techniques, Wu et al²⁵ and Yu et al²⁶ reported a significant decrease in screw insertion time with the use of 3D CBCT image guidance.

24.5 Minimally Invasive Applications of Spinal Image Guidance

The placement of percutaneous spinal instrumentation has increased with the increasing popularity of minimally invasive spinal surgery. Advantages of 3D CBCT image guidance in minimally invasive spinal procedures include the ability to place percutaneous instrumentation with no active fluoroscopy.58,59,60,61,62,63 Additionally, percutaneous placement of pedicle screws without the use of Kirschner’s wires has been reported with 3D CBCT image guidance.^64,65 Another advantage of 3D CBCT image guidance is the ability to register the patient in the surgical position prior to exposing the spine and this has aided some surgeons in more focused approaches to spinal lesions. Kim et al⁵⁵ described their experience in eight patients who underwent successful 3D CBCT image-guided anterior cervical microforaminotomy. Additionally, Rajasekaran et al⁶⁶ have described a minimally invasive approach for removal of osteoid osteomas using 3D CBCT image guidance.

24.6 Case Illustration

A 33-year-old woman presented with a 5-year history of progressive mechanical back pain. After failing extensive conservative therapy, a discogram was accomplished that revealed significant disc derangement with concordant pain at L3–L4 and L4–L5. The patient underwent a two-level extreme lateral interbody fusion (XLIF) at the L3–L4 and L4–L5 levels through a minimally invasive retroperitoneal approach. Posteriorly, 3D CBCT image guidance was used for instrumentation placement. Translaminar facet screws were planned. Preoperative CT revealed thin L4 laminae that would not accommodate translaminar facet screws. The incision for the reference arc was made through the center of her tattoo over the L4–L5 level and the reference arc was attached to the L5 spinous process. The image-guided probe was then used to ascertain the trajectory of the left L3 translaminar facet screw on the skin. Through a stab incision, the image-guided probe was inserted down to the spinolaminar junction and a virtual plan for the translaminar facet screw was set ( Fig. 24.1). This area was exposed with a small tubular retractor and a pilot hole was made at the entry point of the screw as determined by the virtual plan. An image-guided drill guide was then used to drill a hole down the virtual plan ( Fig. 24.2). The hole was then probed to confirm that no bony breach existed and the translaminar facet screw was placed. The right translaminar facet screw was placed in the same fashion. An intraoperative CBCT scan confirmed excellent placement of both screws ( Fig. 24.3). The reference arc was removed and an interspinous plate was used to fixate the L4–L5 level through the same incision. Postoperative AP and lateral radiographs revealed excellent placement of all instrumentation ( Fig. 24.4). At 4-month follow-up, the patient was satisfied with the appearance of her incisions ( Fig. 24.5) and she reported near-complete abatement of her preoperative low back pain. In addition, CT scan revealed solid interbody fusion.

Fig. 24.1 Insertion of the image-guided probe to the spinolaminar junction through a small incision. Inset picture is from the image-guided platform; the probe tip is seen at the spinolaminar junction and a virtual plan is set.

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