HISTORICAL PERSPECTIVE OF ROBOTICS AND IMAGE-GUIDED NAVIGATION SYSTEMS
Although robotics and user-operated image-guided (IG) navigation systems are typically considered mutually exclusive surgical platforms, both are reliant upon radiographic imaging and stereotaxy in order to provide precision and accuracy during spine surgery. Stereotactic techniques have been widely utilized in neurosurgical procedures dating back to as early as 1908 when Horsley and Clarke1 described the use of a stereotactic frame used to lesion targets within the brain of a monkey. The subsequent development of frameless stereotaxy coupled with real-time IG/navigation was optimized for applications in cranial surgery in the 1990s and has been universally adopted across centers throughout the world.2,3 Stereotaxy as applied to the spine has led to the development of both commercially available, IG navigation systems such as the O-Arm (Medtronic Navigation, Medtronic Inc, Dublin, Ireland) with Stealth Station Navigation (Medtronic Navigation). These systems provide real-time, navigated feedback of instruments such as tubular dilators, awls, pedicle finders, taps, screwdrivers, which are maneuvered entirely by the surgeon (Figure 1).
Robotic systems are also reliant upon radiographic imaging and stereotaxis for user-operated trajectory planning, which is then performed by a fully automated robotic arm that “locks” the desired screw trajectory for the surgeon. The first surgical application of robotics was demonstrated in 1985 when a brain biopsy was performed by a modified industrial robot with more accurate and steady guidance when compared to the human hand.4 In 1992, the ROBODOC was the first robot to be employed for orthopedics by boring a hole in the femoral head, allowing surgeons to optimize prosthesis size for total hip arthroplasty.5 Since that time, multiple robotics systems have demonstrated efficacy for surgical use including the AESOP and ZEUS systems.6,7 Developed in conjunction with the Defense Advanced Research Projects Agency (DARPA), the da Vinci Surgical System (Intuitive Surgical, Sunnyvale, California) was the first operative surgical robot approved by the United States Food and Drug Administration and remains one of the most utilized today. The da Vinci robot advanced surgical robotics by creating the first truly immersive 3-dimensional system. However, perhaps the most profound contribution of the da Vinci is that it served to popularize surgical robotics not only for medical professionals, but also the general public. Although both of the IG and robotics systems historically utilized in spine surgery are fundamentally and similarly based upon stereotaxy and pre/intraoperative imaging, robotics systems have lacked the real-time navigation that IG systems utilize. It is important to note, however, that newer robotic systems allow for either entirely user-operated IG or real-time IG along an automated robotic arm trajectory. Because the majority of previously published studies involve either non-navigated robotic or IG systems, these systems will be described within this review as 2 separate entities (which is consistent with their description in the published literature).
APPLICATIONS TO SPINE SURGERY
Surgical robotics systems have been classified into 3 main categories: (1) Supervisory Controlled Systems for which the surgeon plans the surgery offline after which the robot performs the procedure autonomously under close supervision, (2) Telesurgical Systems that allow the surgeon to control the robot remotely in real-time, and lastly (3) Shared-control Systems that allow for the surgeon and robot to directly control the surgical instruments simultaneously.8 The commercially available robotic systems in use today for applications in spine surgery are shared-control systems, which require either pre- or intraoperative imaging in order to plan stereotactic trajectories, which are, in turn, produced by an automated robotic arm. Such platforms first reached the market in the 1990s with varying degrees of success and acceptance in the spine surgery community. The Miro system, which was first developed by the German Aerospace Center, consisted of a robotic arm that positioned a drill guide, a central control, and lastly an optical tracking system.9 The SpineBot (Centre for Intelligent Surgery Systems, Hanyang University, South Korea) uses preoperative computed tomography (CT) scans to plan screw trajectories. Intraoperatively, the robot then guides the surgeon to the preplanned screw trajectory using a robotic arm and holder. This system was successfully tested on 28 pedicles in 2 cadaveric specimens with no screw malpositioning and a total system error of 1.38 mm ± 0.21.10 Two notable telesurgical systems for spinal robotics include the Georgetown Robot and the Spine Bull's-Eye Robot. The Georgetown robot, initially introduced in 2002, consisted of a surgical arm mounted on the operating table that would perform percutaneous procedures designed for minimally invasive spine surgery.11 Likewise, the Spine Bull's-Eye Robot consisted of a surgical arm that would facilitate guide wire placement into pedicles under fluoroscopic guidance. Zhang et al12 demonstrated a 97.1% success rate with pedicle guide wire placement in 206 pedicles using the Spine Bull's-Eye system. Lastly, the da Vinci system (Intuitive Surgical) has been successfully described for use in anterior lumbar interbody fusion, laminotomy, laminectomy, annulotomy, and dural suturing for in vivo porcine models.13,14
While all of the previously described robotics systems involve the automated performance of portions of the surgical procedure, IG systems provide enhanced real-time stereotactic feedback to the surgeon who then uses that information to plan and manually perform the surgical procedure. The utilization of IG has been increasing across centers, with a growing body of literature pertaining to increased accuracy of thoracolumbar pedicle screw placement.15-19 IG relies upon an initial CT scan in order to create the 3-D image used in surgery. The most current systems (for example, the O-Arm with the Stealth Station Navigation [Medtronic]) utilize intraoperative CT acquired while the patient is in the surgical position along with a rigid reference array to the bony anatomy (in either the form of a spinous process clamp or iliac crest pin), thus eliminating the need for anatomic registration (Figure 2). Surgical instruments (tubular dilators, awls, pedicle finders, taps, screwdrivers, etc) with reference arrays are acquired via an optical tracking system, and the surgery is performed utilizing real-time tracking of each particular surgical tool in space (Figure 3).
ADVANTAGES OF ROBOTICS AND IG SYSTEMS
The theoretical advantages of robotic and IG systems in spine surgery are 3-fold: (1) increased accuracy of pedicle screw placement vs historical freehand techniques, (2) minimally invasive applications (small incision, minimal retraction, dissection, bleeding, and infection), and lastly (3) decreased radiation exposure to the operator vs traditional fluoroscopically assisted techniques. Furthermore, robotic systems confer unique advantages in comparison to the human hand, namely an inability to fatigue, elimination of tremor, and precise repetition. Both rely on intraoperative imaging, which obviates the need for the identification of bony anatomic landmarks, thus making both systems appealing for minimally invasive surgical techniques. Because IG systems have been implemented over a longer time period and are more widely utilized among centers, there is a greater body of evidence within the literature that support the 3 abovementioned benefits. However, unlike IG, which has been present in surgical operating rooms for decades, robotics in spine surgery is a more recent surgical application.20 Because of this, there remains a dearth of literature on spinal robotics and controversies persist when comparing outcomes to traditional freehand techniques.
Increased Pedicle Screw Accuracy
Pedicle screw fixation is a commonly utilized technique in thoracolumbar spine fusion, and although techniques have been described for freehand insertion, the learning curve remains steep.21,22 Additionally, insertion can be challenging in cases where anatomy may be altered such as in rotary scoliosis where medial or inferior breaches of the pedicle wall may result in injury to neural elements such as the spinal cord and/or nerve roots. Present studies pertaining to pedicle screw accuracy that utilize various techniques have demonstrated wide variations in suboptimal screw placement rates. These studies involve subjects operated on at various levels with an array of varying pathologies. It is also difficult to control and account for individual differences in a technique among surgeons, particularly in nonrandomized studies. The purported benefits of IG and robotics systems in regard to screw placement must be considered within the context of the experience of a particular surgeon utilizing this technology. Pedicle screw misplacement rates in the thoracolumbar spine using the freehand technique have been shown to range anywhere between 2% and 31% in a large series.23-26 The malposition rate when utilizing 2-D fluoroscopy-based techniques has been shown to range between 2% and 22%.21,22,27 Importantly, the definition of a malpositioned screw is not consistent among studies and should also be considered when comparing techniques. Pedicle screw placement accuracy, in most studies, is based on postoperative CT scans, confirming the presence of the screw within the confines of the pedicle. It should also be considered that the clinical significance of this radiographic confirmation is not well described, as a pedicle screw residing outside of the pedicle by 1 to 2 mm, especially in cases of lateral breach, is likely to be clinically inconsequential.
In regard to accuracy conferred by robotic systems, Devito et al28 performed a multicenter, retrospective review evaluating the use of Spine Assist in the placement of 3271 pedicle screws. They found a clinical acceptance rate of 98% when assessed fluoroscopically in the operating room (OR). One hundred ninety-eight patients were then subjected to CT analysis, and 98.3% of screws were found to be within the 2 mm “safe zone.” Only 1.7% of screws had a breach greater than 2 mm. Pechlivanis et al29 performed a prospective study evaluating 31 patients undergoing percutaneous robot-assisted pedicle screw placement with posterior lumbar interbody fusion (PLIF). They concluded that 91.5% of screws were within 2 mm of planned trajectory on the longitudinal plane and 98.4% in the axial plane. While the study compared screw placement to planned trajectories, it did not comment on pedicle breach in absolute terms. These findings were corroborated in a cadaveric study performed by Togawa et al,30 which found deviation of under 1.5 mm from planned trajectory in 29 of 32 specimens. Kantelhardt et al31 performed a retrospective review comparing conventional freehand vs open robotic-assisted vs percutaneous robotic-assisted pedicle screw placement techniques. The authors found a 94.5% accuracy rate for the combined robotic-assisted group vs 91.4% for the freehand group. A similar study performed by Schatlo et al32 found no statistically significant difference in “clinically acceptable” screw placement (Gertzbein-Robbins A or B) between the conventional fluoroscopically assisted percutaneous screw placement and robotic-assisted placement (open and percutaneous).32 The robotic-assisted group had a statistically significant decrease in blood loss vs conventional freehand placement. The authors concluded that while robotic-assisted screw placement is safe and effective, technical difficulties persist and surgeons must have sufficient knowledge of freehand techniques as a backup.
There are 3 prospective, randomized controlled trials (RCTs) in the English literature that have evaluated robot-guided pedicle screw placement. Kim et al33 compared the accuracy and safety of robot-assisted minimally invasive PLIF vs conventional open freehand techniques. There were no significant differences between the groups for intrapedicular accuracy (P = 0.534); however, the robot group had significantly less proximal facet joint violations (0% vs 15.9%, P < 0.001).33 A 3-arm prospective RCT by Roser et al34 compared pedicle screw insertion techniques through 3 different modalities: fluoroscopically guided freehand, navigation-guided, and robotic-assisted. Unfortunately, the study was significantly underpowered with 10 patients in the fluoroscopy group, 9 patients in the navigation group, and 18 patients in the robot group. Without statistical analysis, the authors concluded that all groups had comparable accuracy and operative time, but cumulative radiation dose was lower in the navigation and robotic groups. In the most well-constructed study to date, Ringel and colleagues35 reported significantly poorer screw placement in the robot group compared to the fluoroscopy group (85% vs 93%), as well as significantly more screws requiring intraoperative revision in the robot group compared to the fluoroscopy group (10 vs 1). The authors concluded that attachment of the robot to the spine and lateral skiving of the implantation cannula at the screw entry point were potential vulnerable aspects of the robotic surgery that led to misplacement.35
To date, very little literature has explored the role of robotics in spinal deformity surgery. Macke et al36 performed a retrospective review of 50 patients who underwent robotic-assisted pedicle screw placement for the treatment of adolescent idiopathic scoliosis. They found a breach rate (>2 mm) of 7.2% of which 3% were medial breach. Such pathologies pose a great challenge for instrumentation as the native bony anatomy and architecture are often distorted. It is likely that these conditions offer the most profound area of opportunity for spinal robotics to improve pedicle screw accuracy.
In comparison to the above-mentioned robotics literature, the data supporting increased pedicle screw accuracy using IG is much more robust. Two RCTs have compared suboptimal screw placement rates using either IG or non-IG techniques. Laine et al performed an RCT of 100 well-matched subjects randomized to either pedicle screw placement with or without IG and demonstrated a significantly lower pedicle perforation rate in the IG group compared to the conventional group (5% vs 13%).37 In another RCT by Rajasekaran et al38 comparing pedicle screw placement accuracy in deformity cases utilizing either an IG technique or 2-D fluoroscopy, a significant decrease in cortical breach rate (2% vs 23%) was seen in the IG group compared to the 2-D fluoroscopy group.
IG can also be an invaluable tool in understanding complex spinal anatomy secondary to deformity, tumor infiltration or in cases of revision surgery with the ultimate goal of decreasing the rate of suboptimal instrumentation placement. A large meta-analysis by Mason et al19 of 30 studies with a total of 9310 pedicle screws placed by either freehand, 2-D, or 3-D-fluoroscopic techniques found malposition rates of 31.9%, 15.7%, and 4.5%, respectively. Another systematic review of 26 prospective studies demonstrated an accuracy rate when utilizing the freehand technique of 69% to 94%, 28% to 85% when utilizing 2-D fluoroscopy, and 89% to 100% when utilizing IG.18 Importantly, it was also shown that screws inserted using the freehand technique were more prone to breach pedicle wall medially.18 In another meta-analysis of 23 studies assessing pedicle screw placement outcomes either with or without IG, Verma et al15 demonstrated a statistically significant increase in screw accuracy when IG was utilized. These results are also supported by 2 other published meta-analyses.16,17
The benefits of IG are also evident in cases involving the pediatric population where anatomy is often disproportionally smaller and can be altered significantly. In a recently published series of 137 screws placed in 16 consecutive pediatric spinal fusions (children age 10 and younger), Luo et al39 reported a significantly higher screw placement accuracy rate (97.8%) using CT-based IG in comparison to previous literature using freehand and fluoroscopic techniques (90.9%).40
More recently, IG techniques have been applied to placement of cervical pedicle screws as prior studies without IG have shown screw malposition rates as high as 14.3% to 29.1%.41,42 Ishikawa et al43 reported a malposition rate of 11.1% (2.8% major pedicle violation, 8.3% minor violation) with IG placement of 108 cervical pedicle screws; however, a more recent retrospective analysis of 310 cervical pedicle screws placed using IG by Shimokawa et al44 revealed a screw malposition rate of only 2.9% (0.6% major pedicle violation, 2.3% minor violation). Theologis and Burch45 showed safe and accurate placement (99% accuracy) of 121 cervical pedicle screws using IG with subsequent significant improvements in clinical outcomes. Application of IG to cervical pedicle screw placement within the pediatric population has been investigated by Kovanda et al46 who demonstrated adequate placement of all 14 cervical screws (including 5 C2 pedicle screws) in 7 pediatric patients under age 10.
While an increasing body of literature continues to confirm the increased accuracy conferred by the use of robotic and IG systems, a thorough understanding of spinal anatomy remains paramount, especially in situations where these systems may fail. Ultimately, the advantages and disadvantages of IG and/or robotic systems should be weighed on a case by case basis taking an individual surgeon's experience and comfort level with the pathology at hand into account.
Radiation exposure to both the patient and operating room staff is a substantial concern when considering the use of any particular intraoperative imaging modality in spine surgery. The International Commission on Radiological Protection recommends no greater than an upper limit radiation exposure of 5 Rem/yr of total body exposure and 50 Rem/yr of extremity exposure.47 Although a prior study by Mulconrey et al48 demonstrated that the yearly maximum number of minutes of fluoroscopic time remains under this value, final radiation exposure to the surgeon and OR staff is highly variable and dependent upon factors such as surgeon and fluoroscopy technician experience. Both robotics systems and IG can significantly limit radiation exposure to the OR staff. With IG and robotics systems, CT and/or fluoroscopy can be acquired with the OR staff outside of the operating room. The procedure then may proceed without additional intraoperative fluoroscopy or CT scans. This is crucial in reducing cumulative radiation exposure for surgeons who perform fluoroscopy-assisted procedures regularly. Smith et al49 compared radiation exposure in pedicle screw placement utilizing either 2-D fluoroscopy or IG and found a significantly decreased mean radiation exposure to the surgeon's torso in the IG group in comparison to the fluoroscopy group (4.33 vs 0.33 mRem). In the IG group, only a single intraoperative CT was performed with the surgeon outside of the operating room which substantially reduced the radiation exposure to surgeon. In a prospective randomized trial comparing radiation exposure using 2-D or 3-D fluoroscopic techniques, Villard et al50 showed that the radiation exposure to the surgeon was 9.96 times higher in the 2-D fluoroscopy group in comparison to the IG group.
Less is known about the impact of IG on radiation exposure to patients. The intraoperative CT scan in the IG technique carries a relatively fixed dose and that must be scrutinized against the more variable doses seen in 2-D fluoroscopy-based techniques. Importantly, one must take into account patient factors such as the operated levels or patient's body habitus when accounting for the variability of radiation doses when 2-D fluoroscopy is utilized. Also, surgeons vary significantly in the number of images they need to perform a particular procedure. A cadaveric study by Tabaraee et al51 found that while radiation exposure to the surgeon was decreased in the O-Arm group in comparison to the C-Arm group, radiation exposure to the cadaver was greater in the O-Arm group. Another study by Mendelsohn et al52 also found an increase in radiation exposure to the patient in the intraoperative CT group when comparing 73 patients that underwent intraoperative CT-based navigation to 73 matched controls in whom 2-D fluoroscopic techniques were used. Costa et al53 reported a cumulative average radiation dose of 5.15 mSv per patient in a series of 107 consecutive patients undergoing intraoperative CT with O-Arm. In the previously mentioned study by Villard et al,50 the average radiation exposure to the patient was found to be greater in the 2-D-fluoroscopy group when compared to the 3-D group; however, this difference did not reach statistical significance (1884.8 vs 887 cGy-cm2). The potential risks of increased radiation exposure to patients using CT-guided navigation should therefore be weighed against the potential benefit of increased accuracy of screw placement (which theoretically could reduce the need for postoperative CT scans and/or revision surgery). Further studies are necessary to better quantify the implications of these differences in radiation exposure between techniques.
In terms of reducing radiation exposure using intraoperative CT, a study by Abul-Kassim et al54 investigating the image resolution conferred by different O-Arm scan settings using both a chest phantom and cadaveric pig spine found that radiation doses can theoretically be reduced 5 to 13 times without negatively impacting the quality of spinal imaging during surgery. Lian et al55 reported an average radiation dose of 5.47 mSv (0.547 Rem) amongst 33 patients when intraoperative helical CT was used. Izadpanah et al56 studied differences in patient radiation exposure between IG and 2-D fluoroscopy during kyphoplasty and found that the IG technique was associated with less radiation exposure.
Minimizing radiation exposure is of greatest importance in the pediatric population as prior studies have suggested a potential correlation between exposure and cancer incidence.57-59 Pediatric deformity cases generally involve instrumenting numerous levels which necessitate multiple 3-D scans, thus increasing radiation exposure. A recent retrospective study of 38 consecutive pediatric scoliosis cases by Kobayashi et al60 found that a mean number of 4 O-Arm scans were required for an average of 11 instrumented levels. This resulted in a mean total radiation dose of 401 mGy per patient which is 80.2% that of the radiation dose of a standard preoperative lumbar helical CT scan.60 In an attempt to minimize cumulative radiation exposure from multiple 3-D scans, Su et al. found that the low-dose protocol, as described above by Abul-Kassim,54 significantly reduced radiation exposure during instrumented pediatric deformity cases using O-Arm by more than half when compared to the prior institutional protocol (1.17 vs 3.83 mSv, respectively).61
Because most robotic systems rely on a limited number of initial 2-D or 3-D-fluoroscopic images for registration purposes, a major theoretical advantage of these systems, like the above-mentioned IG systems, is a reduction of radiation exposure when compared to 2-D fluoroscopic techniques. Kantelhardt et al31 found an average radiation exposure of 34 s for robotic inserted pedicle screws vs 77 s for conventional techniques. Likewise, Schoenmayr and Kim62 reported 40% lower radiation exposure for robotic systems when compared to traditional techniques. In the prospective randomized trial performed by Roser et al,34 the average radiation time for the robotic-assisted arm was 15.98 s when compared to 31.5 s for the traditional freehand technique. Interestingly, this radiation time was still greater than the 10.36 s needed in the navigation-assisted cohort. Further studies are warranted to better delineate the impact of IG and robotics systems on radiation exposures for both surgeons and patients.
IMPACT ON CLINICAL OUTCOMES AND SURGICAL EFFICIENCY
While the impact of robotic systems on clinical outcomes has yet to be demonstrated within the literature, several studies have attempted to assess the impact of IG on clinical outcome with particular emphasis on both neurological injury and reoperation rates for malpositioned screws. In a meta-analysis of 23 studies including 5992 pedicle screws, Verma et al15 reported a lack of statistically significant improvement in outcomes with the use of IG despite a significantly improved rate of accuracy. A more recently published retrospective, single-center clinical outcome analysis comparing the use of O-Arm-assisted navigation with freehand and/or fluoroscopic guidance for thoracolumbar fusion showed a significant decrease in malpositioned pedicle screws (1.6% vs 4.2%) when IG was used.63 More importantly, there were also significant decreases in hospital stay (4.72 vs 5.43 d), spine-related readmission rate (0.8% vs 4.2%), risk of reoperation for hardware failure (2.9% vs 5.9%), and all cause reoperation (5.2% vs 10.9%) in the IG group.63 Furthermore, the O-Arm was found to be a significant predictor of decreased risk of reoperation when analyzing both the cases where greater than and less than 5 levels were instrumented.63 Watkins et al64 found a reduction in the reoperation rate (3%-0%) for inadequately positioned screws when comparing cohorts of 100 patients pre- and postimplementation of an IG-based pedicle screw placement system. Although this improvement was not statistically significant, the authors found a cost savings of $71 286 per 100 cases when using IG for thoracolumbar pedicle screw placement. Further prospective, randomized studies comparing the use of computer-based navigation with fluoroscopic and/or freehand techniques may help further delineate which cases/patient populations may receive the most cost-effective and clinically relevant benefit from IG.
The impact of IG on surgical efficiency and workflow has also been investigated in a recent study by Khanna et al.65 In their retrospective analysis comparing single-level instrumented fusions using either O-Arm or freehand techniques, IG was associated with similar setup times but a significant overall decrease in total operative time compared to the freehand technique.65 A trend toward shorter setup and procedural times was also seen over time in the O-Arm group but not the freehand group, suggesting an initial learning curve associated with the use of computer-based navigation.65 This has also been consistent with our own experience, as this learning curve not only applies to the surgeon but also to the support staff (operating room nurses, radiology technicians, and biomedical engineers) who have over time become more familiar with the equipment setup thus leading to a more efficient workflow in these cases.
Given its relatively short time of clinical use during spine surgery, studies assessing the impact of robotics systems on clinical outcomes and surgical efficiency are still pending. It may be inferred based on the IG literature that, given the increased accuracy of robotics systems, there may be a positive impact on clinical outcomes. As with the implementation of any new technology, a learning curve exists that once overcome, may lead to greater surgical efficiency.
While much of the robotics literature pertains only to thoracolumbar pedicle screw accuracy (because of its early phase of adoption at select centers), IG techniques have become more universally implemented and their application and utility have gone beyond solely the placement of pedicle screws. Several studies have described the feasibility and workflow of IG during minimally invasive lateral lumbar interbody fusion (LLIF).66-68 Joseph et al67 demonstrated appropriate interbody cage placement accuracy at each level in a total of 66 levels treated in both single and multilevel surgeries. Although no direct comparison studies have been performed, the use of CT navigation during both single and multilevel LLIF appears to be safe and accurate with the potential benefit of decreasing overall radiation exposure to the surgeon and patient.68
The application of minimally invasive techniques to sacroiliac (SI) joint fusion has been previously described and is being increasingly performed over open techniques.69,70 More recently, IG has been described in lieu of 2-D fluoroscopic confirmation in 2 patients by Lee et al.71 Despite a ventral sacral cortical wall breach requiring revision in 1 patient, the authors suggest that the auto registration and multiplanar views provided by IG may help surgeons become more familiar with complex pelvic anatomy and thus decrease the overall learning curve associated with SI joint fusion.71
Several studies have also investigated the use of both IG and robotics in the placement of S2 alar screws. Nottmeier et al72 and Ray et al73 have both demonstrated the safety and feasibility of S2 alar screw placement in retrospective analyses of 20 and 18 patients, respectively. Although Nottmeier et al72 reported an anterior screw breach of the sacrum in 5 out of 32 screws while Ray et al73 reported a single breach, none resulted in clinical complications. More recently, Laratta et al74 and Shillingford et al75 demonstrated the safety and feasibility of this type of fixation using a robotic guidance system. The use of IG has also been safely demonstrated in the placement of iliac screws, as real-time visualization of screw trajectory in multiple planes may reduce complications like violation of the SI joint or anterior cortical pelvic wall which are often attributed to lack of clear visualization/unfamiliarity with pelvic anatomy.76
The use of IG has shown utility in the resection of both primary and metastatic spinal tumors. Several studies have reported safe resection of osseous tumors including osteoid osteomas and osteoblastomas with emphasis on preservation of uninvolved structures using IG.38,77-80 Fujibayashi et al81 reported the use of IG in successful en bloc resections of 3 solitary malignant spinal tumors via spinal osteotomy. Dasenbrock et al82 reported the use of user-guided IG for sacral chordoma resection in 3 patients with emphasis on allowing better visualization of the appropriate tissue margins. Vougioukas et al83 reported the use of computer-assisted navigation software in the planning and resection of chordomas involving the craniocervical junction in 3 patients. In regard to the use of IG for intraspinal tumors, a retrospective review by Zong et al84 comparing 51 patients with lumbar intraspinal tumors (12 meningioma, 25 neurilemmoma, 3 epidermoid, 2 cavernous hemangioma, 4 lipoma, 4 metastatic tumors, 1 teratoma, and 1 angioreticuloma) treated either with or without IG found an increased percentage of patients achieving total resection in the IG group (95% vs 86%). Although this difference was not significant, they did find significant decreases in operative time and blood loss in the IG group.84 Maduri et al85 reported safe, gross total resection of 13 consecutive cases of intradural extramedullary tumors via a paraspinal tubular approach with the use of preoperative magnetic resonance imaging merged with intraoperative 3-D IG. In a retrospective multicenter review of 50 patients with spinal column tumors who underwent resection using IG, the authors concluded that IG may help better localize lesions intraoperatively with the ability for real-time feedback that can guide resection and limit injury to collateral tissues.86 Further prospective randomized studies assessing the use of IG in spinal tumor resection will help to better characterize which specific pathology and patient populations may benefit most from its use.
COMMERCIALLY AVAILABLE IMAGE GUIDANCE AND ROBOTIC SYSTEMS
As discussed earlier, intraoperative, IG systems that allow for real-time 3-D navigation involve both an image source combined with stereotactic navigation software. Many of the studies referenced within this review used the O-Arm, an intraoperative cone-beam CT coupled to the Stealth Navigation Station (Medtronic). This form of intraoperative CT (iCT) and navigation system produces 3-D fluoroscopic images and allows for real-time intraoperative navigation of instruments within the surgical field. Importantly, the O-Arm is capable of providing resolution of bony structures only and is therefore incapable of defining soft tissues. More recently, a portable, 32 slice helical CT scanner capable of full Hounsfield soft tissue imaging called the Airo® (Brainlab AG, Feldkirchen, Germany) has been utilized in spine surgery.55 Lian et al55 assessed both the accuracy and surgical time of single-level minimally invasive transforaminal interbody fusion performed on 33 patients using the Airo iCT coupled with the Curve™ navigation system (Brainlab AG) and found a pedicle screw accuracy rate of 98.6% with average operative time of 192.8 min (2.6 min per screw).55 No direct comparison studies have been done between the O-Arm and Airo; however, a prior study does exist comparing navigation software. Nooh et al87 reported a small but significant difference (97.2% vs 96.1%) in a meta-analysis comparing pedicle screw accuracy rates slightly favoring the Stealth Navigation Station (Medtronic) over VectorVision (Brainlab AG). Further studies comparing the O-Arm and Airo would be of particular value, not only in regard to accuracy and radiation exposure, but also in cases of tumor resection where soft tissue visualization may guide resection.
Despite 18 robotic spine systems being described in the literature, there are only 5 commercially available with 3 systems approved by the FDA for use in spinal surgery.88 The Spine Assist, and its later iterations, the Renaissance™ and Mazor X™ (Mazor Robotics Ltd, Caesarea, Israel), was the first robotic spinal system to be approved by the FDA and remains the most published shared-control robotic system in the Unites States. First described in 2006, the Spine Assist consists of a cylindrical device that is mounted to the patient and affords 6 degrees of freedom (Figure 4). There is an associated computer workstation with software that allows for preoperative screw trajectory planning, intraoperative image acquisition, kinematic calculations, and real-time robot motion control89 (Figure 5). An arm with an affixed drill guide will move to the desired pedicle trajectory (Figure 6). The surgeon can then proceed to drill the pedicle allowing for tactile feedback. The Mazor X™ utilizes a fully automatic robotic arm (Figure 7) which obviates the need for the patient mounted track utilized by previous models. The ROSA® robot (Medtech Surgical, Montpellier, France) received FDA approval in 2016. It likewise utilizes preoperative CT scans to assist in planned screw trajectory with the purported advantage of real-time IG to gauge screw depth. The Excelsius GPS™ (Globus Medical Inc., Audubon, PA) most recently gained FDA approval in 2017. Similar to the ROSA® robot, this system combines both real-time IG using preoperative or intraoperative imaging which can be used either manually by the surgeon or in conjunction with an automated robotic surgical arm.
Robotics and IG systems provide significant value in regard to accuracy and decreasing radiation exposure to the surgical team during spine surgery. Newer systems integrating features of both real-time IG and robotics systems are promising, and further studies are necessary to determine instances where these systems provide the greatest benefit in spine surgery.
Dr O’Toole is a consultant for Globus Medical, RTI Surgical, Spinal Elements, and the FDA, and receives royalties from Globus Medical, RTI Surgical. Dr Lehman receives royalties from and provides education for Medtronic and Stryker, and is a consultant for Medtronic. The other authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.
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This manuscript provides a historical perspective on the emergence of robotics and image-guided navigation systems in spinal surgery. The introduction of these advanced technological platforms mirrors the current state of art in other medical, surgical, and non-medical arenas. As the adoption rate increases and solid data is collected to support its clinical and economical value, it is conceivable that the use of such technology will be heavily incorporated in current practice and may be considered “standard of care”. I would like to congratulate the authors on their tremendous effort to compile a very informative article.
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