The evolution of spine surgery has been marked by significant advancements in technology, technique, and approach. The progression from open procedures to the current era of minimally invasive techniques has been largely driven by efforts to improve surgical precision and enhance patient outcomes. Early interventions predominantly relied on conventional open procedures, often associated with significant tissue disruption, prolonged recovery times, and heightened risks of complications. However, advancements in surgical instrumentation, imaging modalities, and navigational techniques have revolutionized the landscape of spinal interventions.

These innovations have led to the emergence of minimally invasive spine surgery (MISS) as a foundation of contemporary surgical care. Spinal disorders represent a pervasive healthcare challenge, affecting millions worldwide and encompassing a spectrum of pathologies ranging from degenerative conditions to traumatic injuries and neoplastic processes [1,2]. Among the most common procedures performed to address these conditions are decompressions, fusions, discectomies, and corrections of spinal deformities, with 455,500 spine fusions and 285,600 vertebral discectomies performed in the United States in 2018 alone [3]. Spine fusion procedures hold the highest mean cost per stay with an aggregate cost of 14,145 million dollars annually [3]. The prevalence of spine-related injury and the potential for improving patient outcomes while reducing postoperative recovery time and complications has driven the demand for advanced surgical interventions.

MISS represents a paradigm shift in spinal surgery, characterized by its emphasis on minimizing tissue trauma, preserving anatomical structures, and facilitating expedited patient recovery [4]. MISS has achieved these outcomes by leveraging innovative techniques and technologies. In this process, the integration of emerging technologies has become increasingly popular in modern spine surgery. From robotic-assisted systems to advancements in surgical site visualization and navigation platforms, surgeons have an array of innovative tools at their disposal to improve accuracy, minimize invasiveness, and mitigate surgical complexities. Such tools include digital 3-dimensional (3D) exoscopes, used intraoperatively for enhanced target visualization for the surgeon and surgical team [5]. Additionally, computer-based navigations have allowed surgeons to precisely maneuver in surgical locations with limited visibility and lighting using real-time cross-sectional images to create interactive, intraoperative visualizations [6]. Robotic systems have also aided in enhancing surgical precision, stability, and control while decreasing radiation exposure [7]. More recently, augmented reality has entered the realm of spine surgery to better track surgical movement by superimposing imaging studies onto the real-time surgical procedure [8]. These advances, while already transformative in their impact, have the potential to further improve accuracy, efficiency, and safety. Most importantly, they provide alternative options for surgeons to be more particular in personalizing the care that each patient receives.

Despite the great potential of current technologies in spinal surgery, certain limitations persist, impeding their widespread adoption. Challenges such as learning curves, high equipment costs, and technological constraints limit their implementation [9,10]. Additionally, more research is needed to assess if significant long-term improvements in patient functionality and pain following MISS can be achieved with these technologies as compared to contemporary techniques. Considering these factors, this review explores and evaluates various technologies in the field of spine surgery, assessing their clinical indications, impacts on patient and providers, and future directions in advancing spinal care.

The introduction of the operating microscope (OM) marked a transformative era in microsurgery, originating in 1962 and extending to spine surgery in 1977 [11]. Renowned for its exceptional visualization, the OM became a standard tool for visualizing spinal structures and abnormalities in MISS. However, the OM has limited maneuverability which forces surgeons to adopt uncomfortable positions for extended periods of time, increasing strain on the spine, head, and neck [5,11,12]. These factors may contribute to avoidable discomfort and fatigue, potentially impacting surgical performance and increasing the likelihood for medical error [13,14].

A primary metric of neurosurgical optics platforms is the provision of intense light and magnification for detailed visualization of critical neural, vascular structures, and tissue differentiation [15]. While traditional microscopes achieve this through a face-to-machine interface, exoscopes have introduced a shift by enabling surgeons to view the surgical field through a digital screen, moving away from direct ‘through-the-lens’ approach and allowing surgeons to visualize target areas without direct engagement with the microscope [16]. Such novel systems have the potential to offer a broad viewing angle and high-resolution image quality similar to OM and endoscopy, and from a distance comparable to that of the OM [13].

This shift may improve aspects of neurosurgery including surgical ergonomics and injury prevention [15,16]. Sustained neck flexion remains a high-risk factor for spine surgeons and a common cause for many musculoskeletal disorders in this field [17]. Spine surgeons exhibit a higher prevalence of musculoskeletal disorders, with 7.1% undergoing surgical intervention for lumbar and 4.6% for cervical disc disease, surpassing disease estimates in the general population [18]. In a study comparing the posture of surgeons utilizing exoscope to OM in anterior cervical procedures, surgeons spent significantly more time in a deviated posture with OM than with the exoscope in both flexion/extension and lateral bending [19]. Similarly, in a study involving 34 neurosurgeons utilizing exoscope system for a microsurgical exercise, participants demonstrated significantly less head/body displacement during the exercise compared to OM [20].

The indication for exoscope systems also extends to educational settings through its capability to provide detailed anatomical visualization to multiple monitors in the surgical suite, expanding the viewing capabilities to more team members and students [21-23]. While exoscopes show promise in addressing limitations associated with OMs, challenges include poor video quality, stereoscopic availability, and a learning curve for surgeons transitioning to exoscope technology [12,13,22]. Despite these challenges, the mobility, ergonomics, and educational benefits of EX systems position them as promising alternatives in numerous surgical settings [21].

Traditional exoscopes function as digital camera systems attached to an adjustable arm that delivers intense light and magnification to the surgical site (Figure 1) [7]. Images are transmitted to high-definition monitors allowing the surgeon and surgical assistant to view neural and vascular structures in real-time, without being limited to the single view of an ocular mount [11,24]. Although configuration will vary across models and designs, exoscopes provide an adjustable distance between the camera lens and surgical field, typically 25 to 50 centimeters [5]. These systems provide a wider field of view and a longer focal distance than OM, with magnification levels ranging from ×4 to ×30 [5,6,13,24].

One of the initial limitations associated with the traditional exoscope was the lack of stereoscopic vision, or depth perception. However, the design of 3D exoscope systems utilizing dual camera technology has created a stereoscopic effect for surgeons with the use of 3D glasses and 3D (Figure 2) [5,11,13,25]. Improvements in digital monitor resolution to provide 4K and ultrahigh definition has been able to improve image sharpness and quality, however, headaches, dizziness, and nausea have been reported in studies using 3D exoscopes due to the use of polarized glasses [5,8]. Studies have assessed the learning curve for 2-dimensional (2D) and 3D exoscope systems among surgical trainees and experienced neurosurgeons. Findings among the use of 2D systems suggested a learning rate and plateau noninferior to that of OM [26]. Experimental trials with 3D systems have also revealed a significant improvement in microsurgical task performances after just 3 task repeats, irrespective of prior experience with OM and with no significant differences in the learning curve between senior neurosurgeons and trainees [27]. These findings emphasize that exoscope systems are not significantly inferior in terms of learning proficiency and may be implemented into training and clinical use without excessive difficulty. Though OM remains the gold standard, the advantageous capabilities and evolving features of exoscope systems present an alternative to traditional microscopes in certain surgical scenarios, with potential shared indications.

The integration of exoscope systems emerged with the introduction of 2D systems, offering comparable image quality and superior comfort to OM. While novel 3D exoscope systems offer advanced capabilities, 2D exoscopes can offer sufficient visualization, particularly in noncomplex cases [28]. In a case study involving lumbar disc prolapse repair, microdiscectomy using a 2D exoscope resulted in an uneventful procedure and symptom relief. The study recommended caution in its use for complex cases, favoring OM, yet acknowledges that experienced surgeons may still employ 2D exoscope systems effectively [28].

Additional studies have conducted side-by-side comparisons of 2D exoscope systems and OM in similar cases, comparing operating time, blood loss, and self-reported surgeon comfort. Specifically, lumbar decompression, laminotomy for disk herniation removal, and anterior cervical discectomy with fusion (ACDF) all exhibited extended operating times with the exoscope, ranging from 5 to 40 minutes longer than their respective microscope procedures [24]. However, the exoscope provided better visualization and comfort in hard-to-reach areas of the surgical site due to the ability to maintain a comfortable and upright position [24]. Robotically controlled hands-free models of 2D exoscope systems have also been utilized and compared to OM regarding visual quality and surgical experience. In the treatment of lumbar disc herniation by discectomy, overall evaluations by surgical teams postoperatively suggest that the 2D exoscope system offered similar visual quality as compared to the OM [29]. However, in the treatment of cervical disc herniation by cervical discectomy, depth perception was given a much lower grade by the team when compared to the OM. There were no surgical complications or intraoperative switches to the OM in all cases [29].

The advent of 3D exoscope systems and their implementation in neurosurgical intervention is rapidly growing (Figure 2) [25]. Enhanced technical capabilities, visual clarity, and application stem from cutting-edge advancements in this technology to meet the demands of contemporary surgical practices. Most studies cited in this section have been published within the last 3 years, highlighting the relevance of investigating the advantages and disadvantages of these systems in various procedures, and a comparison of 3D exoscope systems to traditional OM for MISS.

The feasibility of training and implementation of 3D exoscope systems have been assessed by examining trends in operating time and blood loss in a series of MISS cases. Among 74 procedures, a study demonstrated that the average operating time for microdiscectomy with 3D exoscopes plateaued after 6 cases by the surgical team and after 9 cases for both decompression and lumbar fusion procedures [8]. Surgeons have additionally reported a shorter learning curve in comparison to training in endoscopic technique and noted the main drawback as a need for repositioning and refocusing using the exoscope arm [30].

In an application of 3D exoscope for ACDF, a subjective questionnaire revealed that the 3D exoscope was consistently rated as noninferior to OM for clinical use and as superior in comfort levels for all conducted procedures [5]. The study notes significantly improved intraoperative posture and image quality as compared to previous 2D models, which opens the door for use in more technically demanding spinal procedures [5]. In a retrospective review of 50 patients undergoing ACDF, a comparison of 3D exoscope to OM revealed no significant differences in operative time, blood loss, or postoperative improvement between the 2 groups. Surgeons found the exoscope system’s intraoperative handling comparable to the OM, with higher comfort levels reported in the subjective questionnaire. However, the exoscope was rated as slightly inferior for depth perception and illumination during ACDF procedures when compared to the OM [12]. Similarly, in a cohort of lumbar decompression and ACDF cases performed with 3D exoscope, depth perception and illumination were rated inferior for ACDF compared to OM, although no significant differences were observed in mean operative time, blood loss, or postoperative symptom improvement [14].

A more detailed comparison of the differences in illumination and magnification was conducted in a study analyzing a surgical team’s survey responses following a series of 18 spinal procedures, including ACDF and lumbar decompression. The 3D exoscope system was graded as equal or superior to OM in the categories of handling and structure identification as well as illumination and magnification of the superficial field [31]. However, the illumination and magnification of the deep surgical field was rated as inferior to OM in 61% and 31%, respectively [31]. This expands on the findings of previous studies regarding differences in visualization between OM and exoscope and may help guide decision making when considering the use of 3D exoscope systems in specific surgical scenarios. It is worth mentioning that when comparing magnification and illumination of the superficial and deep fields, the magnification of depth of the operative field was rated better in cervical procedures compared to lumbar procedures [31].

The use of 3D exoscope technology has also been introduced in tumor resection procedures, providing alternative methods for visualizing spine and brain tumors. In a series of 5 intradural extra-medullary tumor excisions, the 3D exoscope technology has been demonstrated as successful, resulting in no complications and offering improved magnification and illumination of the surgical field like that of OM [15]. The novel advancements allowing for the visualization of 5-aminolevulinic acid (5-ALA)-induced fluorescence also mark a significant stride in neurosurgical interventions, addressing previous limitations and introducing the convenience of simultaneous visualization capabilities, distinguishing it from conventional OM. In early preliminary trials of exoscope systems in brain and spine surgery, limitations included a lack visualization for 5-ALA induced fluorescence in tumor resection, necessitating a switch to microscope intraoperatively [11,31]. However, novel 3D exoscope systems have integrated visualization of 5-ALA-induced tumor fluorescence and cases have demonstrated successful visualization and resection in neurosurgical interventions [32-34]. In a prospective clinical trial analyzing the use of 3D exoscope for visualizing 5-ALA-induced fluorescence in high-grade glioma resection in 20 patients, histopathological analysis of 121 collected specimens suggested a 75% sensitivity and 80% specificity for detecting neoplasm, and a positive predictive value of 95% [34].

Advancements in imaging and stereotaxic procedures paired with rapid developments in computation opened the door for 3D reconstructions of surgical sites [35]. The introduction of the C-arm in the 1950s, tomographic imaging in the 1970s, and 3D reconstruction in the late 1990s all funneled into the conventional applications of navigation systems used in spine surgery today [35]. Early computed tomography (CT) had largely been implemented for preoperative reconstructions, but innovation in the field has led to the introduction of modern image-guided navigation systems which allow for a combination of preoperative and intraoperative data for more accurate image-based guidance [36-38]. More recently, advent of the O-arm introduced 360° imaging capabilities which has helped mitigate reconstructive inaccuracy in imaging due to patient positioning and enhanced evaluation of pedicle fixation [35,39].

Surgical navigation systems have attempted to address drawbacks of visualization associated with traditional surgical techniques by providing a fully contextualized image of the operating area and surgical instrumentation (Figures 3 and 4) [36,40]. Markers are placed on surgical instruments and external landmarks of the patient’s anatomy. The navigation software then utilizes real-time imaging and instrument markers to create a digital map of the operating area. The bony landmarks of the patient serve as a reference point for the software to align the digital map with the preoperative imaging [41,42]. While early navigation techniques relied on a frame-based stereotactic technology which required placing rigid bodies at indicated spinal levels to provide fixed reference points for targeting and 3D reconstruction, this method carries various limitations including the need to account for intraoperative variations in patient positioning and lengthened operative time [43,44]. Contemporary frameless navigation systems offer more convenience and flexibility for surgeons and patients by aligning preoperative virtual CT or magnetic resonance imaging (MRI) spine imaging with the patient’s anatomy, a process known as registration [45]. Operating room setup comprises several key components, including a navigation console, which runs the navigation software, and high-resolution display monitors positioned within the surgeon’s line of sight to provide real-time visual feedback during the procedure [45]. Central to the system is the tracking setup, which may include infrared cameras placed around the operating room to track reflective markers attached to the patient and surgical instruments [45]. Intraoperative imaging, such as fluoroscopy or intraoperative CT/MRI, are utilized to provide real-time images during surgery, further ensuring accuracy. The workflow includes patient registration, aligning preoperative imaging data with the patient’s anatomy using anatomical landmarks or surface matching techniques, and instrument calibration to ensure that all surgical instruments are correctly tracked by the navigation system. Throughout the procedure, the navigation system provides continuous real-time guidance, allowing the surgeon to navigate to the target area with precision [46].

Surgical navigation systems can be utilized for a variety of surgical indications and have demonstrated efficacy in both orthopedic and neurosurgical procedures. Procedures include tumor resection, spinal deformities, adolescent scoliosis, spinal trauma, interbody fusions, foraminal stenosis, degenerative disease of body, facet, or disc, spondylolisthesis, and rheumatoid arthritis [34,47]. The efficacy of navigation systems has been analyzed largely through comparisons of this technology to unnavigated procedures in pedicle screw placement. Reviews of pedicle screw insertion utilizing navigation systems suggest that the most common indications among adult populations include spondylolysis, spondylolisthesis, osteochondritis, post laminectomy, and scoliosis surgery [48,49]. Comparing fluoroscopy-based navigation to traditional methods showed that surgical navigation systems decreased cortex penetration by 62% [50,51]. Results from a systematic review analyzing differences in pedicle screw insertion accuracy between conventional methods and navigation technology showed a decreased risk of pedicle perforation with CT navigation in most in vivo studies [49]. An analysis of 11 other studies examined the success rate of 7,498 pedicle screws placed. 5,963 of the screws (79%) were placed using CT-guided navigation systems, 520 (7%) were placed using fluoroscopy-guided systems, and 1,015 (14%) were placed with conventional techniques. For each modality, accuracy rates were calculated: CT-based and fluoroscopy-based systems demonstrated a 97.7% and 87.8% accuracy rate, respectively, as compared to a rate of 79.5% for free-handed techniques [50-59]. When compared to fluoroscopy-based navigation, CT-based systems have shown a significant increase in accuracy relative to conventional methods [52,53,55,60,61]. Notably, pedicle screw placement was shown to improve with navigation systems regardless of the spinal level [52,62].

Though navigation techniques are associated with improvements in pedicle screw placement and thus lower complications and reoperation rates, such benefits may come at the expense of relatively longer operation times and increased radiation exposure. Among conventional, fluoroscopy, and navigation methods for pedicle screw placement, CT navigation demonstrates higher perioperative time requirements for spine surgery. This is likely due to the preoperative imaging and the image registration process [48,49,63]. The extent of radiation exposure is subject to surgical protocol for respective procedures which necessitates optimization of navigation techniques to balance patient safety and surgical accuracy. Studies indicate that advanced navigation systems in spine surgery significantly reduce radiation exposure to surgeons, particularly CT and O-arm interventions, by allowing them to stand away from the radiation source during imaging [64,65]. However, these systems tend to increase patient radiation exposure due to the need for multiple and high-resolution images for accurate navigation [49,66]. A retrospective analysis of dosimetric data from 101 patients receiving CT navigated spine surgery analyzed the number of acquisitions, total radiation dose, and dosimetric differences between various surgical indications. Results indicate that mean acquisition number and cumulative patient radiation exposure is higher in more major surgeries including spinal deformity correction [66]. Various studies highlight the need for careful balancing of the benefits of navigation accuracy with the radiation exposure risks, recommending minimized acquisitions and tailored approaches based on surgical complexity [49,65,66]. Understandably, there has been hesitance in accepting navigation systems as ubiquitous surgical tools due to the steep learning curve and few studies have shown the exact effect on surgeons’ mentalities regarding procedures [45]. Similarly, few studies have analyzed the cost-effectiveness of navigation systems from a practitioner’s perspective.

The first usage of robotics noted in the field of surgery dates to 1985 when The Programmable Universal Machine for Assembly was used to collect stereotactic brain biopsies [67]. Since this advancement, robotic technology has progressed into usage across the field of medicine, including spine surgery. Seven different robotics systems are approved by the Food and Drug Administration for usage in spinal procedures [68]. These systems are headlined by the da Vinci system which revolutionized minimally invasive procedures [69]. Current systems range from autonomous control with only supervision by the surgeon to direct control of the robotic system [70]. Even with the expansion of robotic spine systems, the transition into the usage of this technology has been slowed by many surgeons. One of the main barriers in this transition is the inadequate or lack of training resources that are available with the new technology [71]. Another barrier to entry into the operating room for this technology is the high upfront cost of equipment. Despite these barriers, surgical systems have shown promise in improving surgical outcomes and physician experience.

Robotic systems have shown a great improvement in accuracy of pedicle screw placement over conventional hand placements (Figure 5) [72]. Accuracy of pedicle screw placement has been demonstrated to be 98.74% through usage of a robotic guided system with intraoperative repositioning [73]. These results were repeated in a study which demonstrated a pedicle screw accuracy of 97.9% compared to preoperative planning with none requiring revised placement [74]. Blood loss, surgical time, and postoperative length of stay have been decreased in the usage of robotics assisted minimally invasive surgery in comparison to traditional open procedures [75]. Not only have robotic systems demonstrated a higher level of accuracy, but they have also shown promise in decreasing harm by radiation, with decreases in procedure time and radiation exposure. Radiation exposure has been found to be 9.96 times higher for the surgeon when robotic navigation systems were not used [76,77].

Similarly, robotic systems have demonstrated themselves to be cost effective options due to lower rates of revisions and complications [78,79] demonstrated similar cost-effectiveness as $608,546 would be saved during a 1-year period at an academic center performing 557 elective thoracolumbar instrumentation cases through the usage of robotic technology. These results demonstrate a clear improvement in surgical outcomes and processes through the implementation of robotic systems. However, usage remains scarce, and propositions have been made for curriculums to aid in the transition of robotics into mainstream usage by surgeons [80].

The landscape of spine surgery has evolved significantly over the years, driven by technological advancements aimed at improving patient outcomes, reducing morbidity, and enhancing surgical precision. The transition from conventional open procedures to minimally invasive techniques has modernized spinal interventions and offered benefits such as reduced tissue exposure, faster recovery, and improved surgical accuracy.

Among the innovative technologies shaping modern spine surgery, exoscope-assisted procedures have emerged as promising alternatives to traditional microscopes. These systems offer enhanced visualization and may mitigate the risks associated with prolonged surgical procedures and surgeon fatigue. Similarly, the integration of navigation systems has revolutionized spinal surgeries by providing real-time surgical guidance. Additionally, robotic systems have shown promise in enhancing surgical outcomes, with increased accuracy and reduced recovery times.

Despite their distinct functionalities, these innovations share common objectives to prioritize precision and accuracy in surgical interventions. The shared objectives are achieved through unique routes including the ability to increase surgical visualization capabilities and intraoperative guidance. Benefits inherent in these technologies, provide surgeons with clearer views of the surgical site and enabling intricate procedures through smaller incisions. Moreover, there is a need to continue improving the accessibility of these technologies, with efforts to reduce the cost barriers associated with acquiring and implementing these technologies.