INTRODUCTION
Lumbar disc herniation (LDH) is one of the most common causes of low back pain [1], with an incidence rate between 3.7% and 5.1% [2]. Surgical intervention, as a primary treatment option [3], can alleviate nerve compression caused by LDH, thereby reducing symptoms and improving function [4,5]. Minimally invasive spinal surgery offers advantages such as minimal trauma, less bleeding, faster recovery, and fewer complications, enabling patients to quickly resume normal work and daily activities [6]. And it has been recommended as the preferred surgical approach for LDH radiculopathy by the North American Spine Society’s 2013 evidence-based guidelines [7]. Transforaminal endoscopic lumbar discectomy (TELD) is a representative technique that uses endoscopes inserted through small incisions, thus minimizing trauma. With the aid of fluid media and highdefinition endoscopic visualization, surgeons can achieve more effective hemostasis and anatomical identification [8]. However, current endoscopic surgeries have some limitations. Firstly, achieving an accurate and reasonable puncture trajectory demands extensive experience [9], and inexperienced surgeons may require repeated fluoroscopies, resulting in high radiation exposure. Moreover, unlike open surgery, endoscopic procedures cannot observe surrounding anatomical landmarks directly, increasing the risk of losing anatomical position in the field of view and damaging important tissues such as nerve roots. These factors significantly increase the difficulty and learning curve of endoscopic surgery, limiting its widespread adoption. Therefore, reducing the difficulty and improving the accuracy of TELD is a critical issue.
In recent years, digital navigation technology has matured and been applied to spinal surgeries. Guided by navigation devices, surgeons can obtain real-time intraoperative imaging and track surgical instruments, significantly enhancing the precision and safety of the procedures. The effectiveness and safety of TELD assisted by optical or electromagnetic navigation have been well documented [10,11]. Recently, a new navigation system has integrated optical and electromagnetic navigation into a single device, offering the advantages of simultaneous optical and electromagnetic tracking with seamless mode switching. We utilized the C-arm-based integrated optical and magnetic surgical navigation system to assist surgeons in performing TELD and compared the clinical outcomes with those of patients who underwent TELD using traditional x-ray fluoroscopy. The objective of this study is to provide reference and theoretical basis for the clinical promotion of this new technology.
MATERIALS AND METHODS
1. Trial Design and Patient Population
From November 2022 to December 2023, data from patients who underwent TELD for LDH at our hospital were retrospectively analyzed. Based on the treatment approach, patients were categorized into 2 groups: the control group (underwent TELD with x-ray fluoroscopy assistance) and the navigation-guided TELD (Ng-TELD) group (underwent TELD with navigation guidance).
This study was performed according to the Helsinki Declaration and approved by the Human Research Ethics Committee of Beijing Chaoyang Hospital (2023-ke-532), which classified it as a retrospective audit and approved access to the patient data used in this research. Written informed consent was obtained from the individual(s) for the publication of any potentially identifiable images or data included in this article.
All patients were followed up by an independent observer, with the follow-up period extending to July 2024 and an average follow-up duration of 11.8 months (range, 7–18 months).
Inclusion criteria: (1) single-level LDH, (2) severe lower limb radicular pain as the primary complaint, (3) ineffectiveness of conservative treatment for more than 3 months, (4) symptoms consistent with imaging findings, (5) American Society of Anesthesiologists physical status classification system class I–III.
Exclusion criteria: (1) central-type disc herniation at the affected level; (2) history of lumbar fractures, infections, tumors, or previous surgeries; (3) presence of spinal instability, cauda equina syndrome, or severe osteoporosis; (4) bleeding disorders; (5) loss to follow-up or incomplete data.
2. Preoperative Management
Aside from the differences in navigation methods, both groups received identical adjunctive treatments. Upon admission, routine hematology and biochemistry tests were completed, and imaging examination were conducted to confirm the affected segment and extent of the LDH. All surgeries were performed by the same team of surgeons.
3. Surgical Technique
All surgeries were performed under local anesthesia (1% lidocaine) with patients in the prone position. Standard iodine and alcohol disinfection were applied, and sterile drapes were placed.
In the Ng-TELD group, the integrated optical and magnetic surgical navigation system (model ZETNa, BOSSCOME, Chongqing, China) was used. Once the surgical area was prepared, a reference tracker was gently secured to the posterior superior iliac spine using either an iliac crest fixation device or adhesive tape, ensuring delicate handling throughout, and connected to the computer mainframe (Fig. 1A) for real-time calibration. A C-arm (Fig. 1B) was used to scan and transfer images to the navigation workstation for automatic registration and reconstruction (Fig. 1C), providing coronal and sagittal spinal images. The entry point, direction, and depth were planned. The surgical instruments were registered (Fig. 1D), and an operating channel was established under navigation guidance (Fig. 1E).
In the control group, the operating channel was established under C-arm x-ray guidance. Based on the patient’s preoperative magnetic resonance imaging (MRI) images, the entry point for the needle was located 8–10 cm lateral to the symptomatic side of the spinous process. The puncture needle was inserted with a 15° caudal tilt and a 20° ventral tilt, reaching the anterior-lateral aspect of the superior articular process of the vertebral body. After confirming the correct position, the needle core is removed, and a guidewire was inserted. The skin was incised, and sequential dilation was performed using dilators. The central catheter was implanted, followed by the bone channel dilation and placement of the working channel and the intervertebral foramen endoscope. Under endoscopic visualization, fat and ligament debris were removed, and the protruding intervertebral disc tissue was excised. The ligamentum flavum was partially resected to expose the dura mater. The dura was retracted medially to expose the nerve root, and the herniated disc tissue beneath the nerve root was removed to fully decompress the nerve root. The nerve root was rechecked for any additional decompression needs. Finally, the working sleeve and intervertebral foramen endoscope were removed, and the incision was closed with sutures. Corresponding to the above text, we present the recent surgical operation video (Supplementary video clip 1).
4. Postoperative Management
The postoperative management was identical for both groups of patients. Pain relief and neurotrophic medications were administered as appropriate. Patients were instructed to perform lumbar and back muscle exercises. Starting 2 days postsurgery, patients were allowed to engage in activities while wearing a lumbar brace. The brace was to be worn for 3 months, during which excessive lumbar movements were to be avoided.
5. Clinical Outcomes
Baseline data and disease information were recorded. Surgical duration, intraoperative fluoroscopy count, and hospital stay length were documented. Total surgery time was measured from the completion of sterilization draping and endoscopic instrument assembly, including the preparation time for the navigation system, and ended when the dressing was applied. Due to the minimal and unmeasurable intraoperative blood loss, it was excluded from the analysis. Postoperative short-term pain was assessed using the visual analogue scale (VAS) one week after surgery (around the time of discharge) to avoid interference from short-term pain caused by the invasive fixation of the reference tracker. The medium- to long-term outcomes were evaluated using the VAS score at the final follow-up. The Oswestry Disability Index (ODI) was employed to evaluate the degree of disability preoperatively and at the final follow-up. The EuroQol VAS was used to assess patients’ quality of life preoperatively and at the final follow-up. Surgical outcomes were evaluated using the MacNab criteria (excellent, good, fair, poor). During the follow-up period, symptom recurrence, complications, and other adverse events were recorded.
6. Statistical Analysis
Data were analyzed using IBM SPSS Statistics ver. 25.0 (IBM Corp., Armonk, NY, USA). The distribution of data was evaluated using the Kolmogorov-Smirnov test. Continuous data conforming to normal distribution were expressed as mean±standard deviation, while categorical data were presented as frequencies and percentages. The independent samples t-test was used to compare normally distributed data between groups. The Mann-Whitney U-test was employed for comparing nonnormally distributed data between groups, and Fisher exact test was used for comparing binary categorical data between groups. Repeated measures data that were normally distributed were analyzed using Repeated Measures Analysis of Variance, followed by Bonferroni adjustments for multiple comparisons. Continuous efficacy indicators before and after surgery were evaluated using paired sample t-tests. A p-value (2-tailed) < 0.05 was considered statistically significant.
RESULTS
1. Study Population
According to the inclusion and exclusion criteria, a total of 61 patients were enrolled (Table 1). Among them, there were 31 patients in the control group and 30 patients in the Ng-TELD group. The average age of the patients was 49.90 years, and the time from symptom onset to surgery was 10.65 months. There were 34 male patients (55.7%) and 27 female patients (44.3%). Symptoms were predominantly right-sided in 33 patients (54.1%) and left-sided in 28 patients (45.9%). The surgical segments were L3–4 or above in 14 patients (23.0%), L4–5 in 31 patients (50.8%), and L5–S1 in 16 patients (26.2%). During the procedure, 15 patients (24.6%) underwent noninvasive reference frame fixation using adhesive tape, while 46 patients (75.4%) had the reference frame secured using an invasive method with an iliac crest fixation device. There were no significant differences in baseline characteristics between the 2 groups (p> 0.05).
2. Clinical Outcomes
Postoperative radiating leg pain and lower back pain significantly improved in the patients (Table 2). The mean preoperative VAS score for radiating leg pain was 6.30± 0.99, which improved to 1.66± 0.70 one week postoperatively and further improved to 0.62 ± 0.61 at the final follow-up. Lower back pain improved from a preoperative score of 4.11± 1.76 to 1.69± 0.77 one week postoperatively, and to 0.84±0.61 at the final follow-up. The differences in VAS scores at different time points were statistically significant (p< 0.05). The ODI showed significant improvement, decreasing from a preoperative score of 58.23%± 8.62% to 8.56%± 3.27% at the final follow-up. These differences were statistically significant (p< 0.05). There were no significant differences between the control group and the Ng-TELD group in terms of various efficacy evaluation indicators at the same time points (p> 0.05).
The additional average preparation time required for the navigation device was 5.03 ± 1.38 minutes. The Ng-TELD group had significantly shorter total surgery time (58.43± 12.37 minutes vs. 83.23± 25.90 minutes), puncture and catheter placement time (5.83± 1.09 minutes vs. 15.94± 3.00 minutes), and endoscopic decompression time (47.17± 11.98 minutes vs. 67.29± 24.23 minutes) compared to the control group. And the number of fluoroscopy sessions was also significantly lower in the Ng-TELD group (3.20± 1.45 vs. 16.58± 4.25). All these differences were statistically significant (p< 0.05). But there was no significant difference in hospital stay length between the 2 groups (p> 0.05).
During the follow-up period, a total of 5 adverse events (8.2%) occurred (Table 2), with 3 cases (9.7%) in the control group and 2 cases (6.7%) in the Ng-TELD group. One patient in the control group had insufficient decompression. Each group had one patient with postoperative nerve root dorsal side injury, manifesting as numbness in the affected limb. These patients recovered by the 3rd and 4th weeks postoperatively after receiving neurotrophic treatment and electrical stimulation. Additionally, 1 patient in each group experienced recurrence at 6 months and 8 months postoperatively, respectively. There were no cases of spinal cord hematoma, organ injury, muscle strength reduction, or the need for revision surgery. There were no significant differences in complications between the 2 groups (p > 0.05). At the final follow-up, according to the MacNab criteria, 57 patients (93.4%) were rated as excellent, 3 patients (4.9%) as good, and 1 patient (1.6%) as fair, the overall excellent and good rate of 98.4%. In the control group, 1 patient (3.2%) was rated as good and 1 patient (3.2%) as fair, while in the Ng-TELD group, 2 patients (6.7%) were rated as good. There was no significant difference (p> 0.05).
3. Case Report
A 28-year-old male patient had been experiencing right-sided lower back pain for 3 years, accompanied by pain in the right posterior thigh, lateral calf, and dorsum of the foot. He had previously received conservative treatment, but the symptoms recurred. Over the past month, the pain had worsened, and numbness had developed in the right lower limb. MRI revealed L4–5 disc degeneration and prolapse (Fig. 2A), with significant posterior right protrusion, right foraminal stenosis, and significant nerve root compression (Fig. 2B). The patient underwent Ng-TELD after admission (Fig. 2C–E). Postoperatively, his back and leg pain significantly relieved, and he was discharged on the third postoperative day. A follow-up MRI at 3 months showed a reduction in the protrusion of the L4–5 disc (Fig. 2F) and significant relief in nerve root compression (Fig. 2G). During the 9-month follow-up, there was no recurrence of back or leg pain, and the lumbar spine and lower limb function, including sensation, were good without complications.
DISCUSSION
Studies have shown that surgery provides more stable medium to long-term efficacy for LDH patients compared to conservative treatment [12]. With advancements in surgical techniques, physicians are aiming to minimize surgical trauma. TELD, as a representative of minimally invasive spinal surgery, has been confirmed by numerous studies for its clinical efficacy [13]. Its effectiveness in treating LDH is comparable to that of traditional surgery [14], with improvements in pain and functional status showing no difference in medium- to long-term follow-ups, and may even be superior [15]. In this study, patients treated with TELD showed significant improvements in pain, spinal function, and quality of life, further validating the surgical efficacy of TELD. The relief of these symptoms was immediate, and the recurrence rate was very low, indicating stable medium-term efficacy. Due to the avoidance of extensive paraspinal muscle dissection and alterations to the bony anatomical structure, patients recovered rapidly postoperatively, with an average discharge time of 5 days, which is better than open surgery. Additionally, TELD-treated patients had smaller surgical scars and required less anesthesia and opioid medication [16]. However, the learning curve for TELD is steep. During surgery, physicians need to puncture the optimal position and then insert the working channel and complete the decompression based on their experience. Physicians typically need to perform 15 procedures to gradually become proficient with this technique [17]. Postoperative outcomes are significantly related to the surgeon’s experience [18]. Inexperienced operations during the long learning process often lead to incomplete decompression or even damage important structures such as nerves or blood vessels. For patients with a high iliac crest or highly migrated disc herniations, even experienced doctors face significant surgical risks.
Optimizing spinal endoscopic techniques is a current hot topic. The selection of the puncture site and precise placement of the working cannula are core aspects of the procedure [19]. This process largely relies on repeated x-ray fluoroscopy to locate anatomical landmarks, which increases surgical duration and intraoperative radiation exposure. Prolonged radiation exposure has significant health implications for the operating staff [20]. Therefore, it is crucial to reduce fluoroscopic exposure for both surgeons and patients to lower the risk of radiation-induced conditions. The computer navigation system, utilizing the C-arm, acquires spinal imaging of the patient and provides real-time guidance for procedures such as puncture and foraminal stenosis, helping physicians avoid bony obstructions during the puncture process. Physicians use imaging fluoroscopy only at key steps [21], thereby better controlling radiation exposure. Compared to traditional x-ray fluoroscopy, navigation significantly reduces the number of fluoroscopic exposures (3.20± 1.45 vs. 16.58± 4.25), and is markedly lower than the average fluoroscopic exposure of 11.71 times observed in experienced physicians at other centers [22]. Furthermore, several studies have shown that navigation assistance notably improves the accuracy and stability of the physician’s operations [23-25]. However, in this study, no significant differences were observed between the 2 groups regarding efficacy indicators and complications. On one hand, this may be due to the small number of cases included in this study. On the other hand, as Vardiman et al. [26] have concluded, navigation systems can help less experienced physicians overcome the learning curve more quickly and partially compensate for a lack of experience [27]. Therefore, our experienced spinal surgery team might extend the surgery time to ensure efficacy, which is another reason for the lack of significant difference in adverse events between the 2 groups. Under local anesthesia, an extended surgical duration inevitably decreases the patient’s trust in the procedure. Navigation-assisted devices can map the anatomical landmarks and guide surgical paths in real time, improving procedural efficiency [28,29]. Although it is undeniable that setting up navigation equipment requires some additional time, this impact is relatively minor. As outlined in the methods section, the preparation of the navigation system primarily involves steps such as placing the receiver, installing the magnetic field generator, performing fluoroscopic imaging, transferring images, and registering the surgical instruments. While these steps may seem fragmented, many can be performed simultaneously, and each takes only a short amount of time, allowing an experienced team to complete the setup swiftly. In our study, the additional time required to assemble the navigation system was only 5 minutes, which did not significantly affect the overall surgical efficiency. Notably, the time required for TELD under navigation was reduced by nearly half an hour compared to the time needed under x-ray fluoroscopy (58.43± 12.37 minutes vs. 83.23± 25.90 minutes), and was shorter than the average surgical time reported by experienced surgeons at other centers (62.2–75.0 minutes) [30,31]. It was also less than the operation time reported in previous studies using standalone electromagnetic navigation [32] or optical navigation [33]. Additionally, we observed another phenomenon: under navigation assistance, the time required for puncture, cannulation, and endoscopic decompression was significantly reduced, indicating that physicians receive continuous guidance throughout the entire procedure. Spinal endoscopic surgery failures are often related to inadequate decompression [34]. Under navigation, the interaction between instruments, vertebrae, and intervertebral discs is clearly and precisely visualized. The endoscope and surgical instruments used during the procedure can be registered with the navigation system, allowing for full visualization during decompression. Surgeons can observe the maximum safe distance the surgical instruments can reach in real time, enabling appropriate removal of the herniated disc and achieving thorough decompression. This significantly reduces the risks of losing orientation under the endoscope, insufficient or unnecessary decompression, and injury to blood vessels and nerves, thereby shortening the operation time, avoiding unnecessary damage, and enhancing patient satisfaction [35]. The complication rate for treated patients was only 6.7%, with no cases of incomplete decompression or disc collapse in the Ng-TELD group, and these minor complications allowed for rapid recovery.
In addition, the benefits of navigation systems for healthcare institutions are also noteworthy. Firstly, the use of navigation systems significantly shortens surgical time, thereby improving overall surgical turnover efficiency. Secondly, navigation assists surgeons in addressing complex anatomical challenges, enhancing surgical precision, and thus increasing the hospital’s capacity to manage more complex cases. Furthermore, with the precise guidance provided by navigation, unnecessary damage and intraoperative complications are minimized, leading to higher patient satisfaction and improved hospital reputation. More importantly, from the perspective of medical education, the application of navigation also presents substantial advantages. Due to limited spatial understanding and practical/anatomical experience, junior surgeons often find it challenging to master TELD. Navigation reduces radiation exposure, thereby minimizing health risks during the learning process. Moreover, the comprehensive support offered by the navigation system simplifies the establishment of the surgical pathway and completion of decompression, enabling young surgeons to smoothly overcome these 2 core steps of TELD. This not only accelerates their learning curve but also boosts the confidence of novice surgeons, facilitating the broader adoption of the technology [32]. Undoubtedly, the introduction of navigation systems increases healthcare costs. However, considering factors such as fewer adverse events and shorter surgical times, the implementation of navigation systems could still bring considerable benefits to hospitals—a conclusion validated by Menger et al. [36]. Nonetheless, this conclusion may vary depending on the hospital infrastructure and regional context. Future research should continue to explore the clinical utility and cost-effectiveness of different navigation technologies to provide more informed decision-making guidelines for healthcare institutions [37].
Given the successful application of navigation systems in spinal surgery, navigation technology has progressively gained wider adoption and has undergone continuous refinement over the years. As early as 2009, endoscopic spine surgeons in Korea pioneered the integration of navigation-guided lumbar decompression with endoscopic spine surgery. Today, various navigation devices are already being applied in clinical practice, the most commonly used surgical navigation systems include ultrasound navigation, optical navigation, and electromagnetic navigation, each offering distinct advantages that contribute to the ongoing advancement of minimally invasive spinal procedures [38]. Ultrasound navigation provides positioning by emitting and receiving ultrasound waves. It is cost-effective, simple to operate, noninvasive, and free from radiation. However, it suffers from low signal-to-noise ratio, high image noise, and poor image quality. Additionally, ultrasound waves attenuate in bone, creating strong acoustic shadows that obscure the surgical area and lead to positioning inaccuracies [39]. Optical navigation is the mainstream system, using binocular or multi-eye vision principles to track premodeled surgical instruments and fixed reference frames. It offers high accuracy but cannot accurately track non-rigid instruments like puncture needles due to premodeled instrument models [40]. Moreover, light path occlusion and image drift also affect navigation accuracy. Electromagnetic navigation systems use signals received by coils and magnetic field emitter positions for localization, allowing them to penetrate objects in the surgical area, avoid light path occlusion, and navigate deformable surgical instruments such as puncture needles. However, they are susceptible to electromagnetic interference and have lower accuracy compared to optical navigation, limiting their clinical application [41]. In this study, a novel integrated optical and magnetic surgical navigation system was employed, connecting optical and electromagnetic devices to the same host and operating within a unified system. This system achieved integrated registration and synchronization of optical and electromagnetic navigation spatial coordinates with imaging coordinates through spatial transformation and accuracy optimization algorithms, ensuring navigation precision. The Ng-TELD group exhibited a 100% excellent rate in postoperative MacNab scores. Additionally, the system allows for seamless switching between optical and electromagnetic navigation, enabling physicians to detect navigation drift in real-time, track deformable instruments, and avoid electromagnetic interference from metal instruments. This integration overcomes the limitations of both optical and electromagnetic navigation, providing complementary advantages and significantly improving puncture positioning accuracy. The navigation system used in this study is a 2-dimensional navigation system, which is more user-friendly compared to other systems. The two-dimensional navigation, performed through C-arm fluoroscopy in the anteroposterior and lateral views, aligns with the surgical habits of endoscopic procedures. It eliminates the need for preoperative and intraoperative computed tomography localization, significantly reducing fluoroscopic exposures for both physicians and patients.
However, several issues were identified with this system during its application. Firstly, as mentioned earlier, the use of navigation devices undoubtedly increases the time required for preoperative preparation. Additionally, computer navigation relies on algorithms that involve complex processes such as localization and registration; any issues in these processes can lead to navigation inaccuracies. On the other hand, patient movement under local anesthesia can affect the accuracy of navigation, so future studies might consider the use of general anesthesia for some patients. To prevent locator displacement during the procedure, it is advisable to fix the locator to the iliac spine to enhance stability and verify its accuracy through fluoroscopic checks. Any deviations should be promptly re-registered [42]. Despite these limitations, the new navigation system has already exceeded expectations in clinical benefits and has integrated advantages that other navigation systems cannot match, showing promising clinical prospects.
There are some limitations to this study. Firstly, since optical-magnetic navigation is a new technology, the number of cases included in the study is limited. Although the average follow-up period of 11.8 months is sufficient for a nonfusion surgery patient cohort [43], extending the follow-up period may provide additional insights. Lastly, the single-center retrospective study design inevitably introduces some confounding factors. The invasive fixation method may cause additional mild postoperative pain. Although the fixation method was randomly selected, it is necessary to pay closer attention to this issue in future studies to minimize potential bias. In the future, we plan to conduct a multicenter large-sample randomized controlled prospective study to further analyze the clinical guidance effects of optical-magnetic navigation and to expand its application to other surgeries or conditions, continuously improving this technology in practice.
CONCLUSION
In summary, the new integrated optical and magnetic surgical navigation system combines the advantages of both optical and electromagnetic navigation. It effectively assists physicians in selecting puncture points for TELD, establishing working channels, and performing disc decompression. This system significantly reduces radiation exposure for both physicians and patients, and shortens operation time, demonstrating a strong potential for future applications.
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