Intraoperative O-arm navigation yields 100% accuracy in pedicle screw placement for adolescent idiopathic scoliosis: a single-institution study

Introduction

Adolescent idiopathic scoliosis (AIS) is a progressive spinal deformity diagnosed once lateral spinal curvature (i.e., the Cobb angle) reaches or exceeds 10 in a patient between 10 and 18 years old that does not have an underlying condition as a cause. It is the most common form of scoliosis with a prevalence ranging between 1% and 3%, and it is more commonly seen in girls. Two-thirds of AIS patients experience worsening of their spinal curve during adolescence, with progression more likely to continue into adulthood in those whose curves exceed 45–50° at the end of growth. In these patients, treatment focuses on reducing the rate of curve progression before they reach skeletal maturity through brace treatment or surgery for more severe curves (1). In patients who pursue surgical treatment, the goal of spinal instrumentation and fusion is to minimize further disease progression and maintain function through operative fixation, reaching satisfactory coronal correction while preserving or improving alignment of the spine in the sagittal plane.

To this aim, pedicle screws are an established means of stable spinal fixation followed by corrective de-rotation, correction of angular deformity, and manipulation followed by fusion (2). In spite of these advantages multiple complications from the use of pedicle screws have been reported. These include spinal cord or nerve root compression resulting from screw malposition, major vessel injury, pseudoarthrosis, and a risk of revision from unsatisfactory bone purchase (2,3). These risks can be exacerbated when attempting to place screws in smaller pedicles, such as those seen in adolescents and the cervical spine (4). Cadaveric studies show that 83% of cervical vertebrae in adults have an inner pedicle width that is less than 3.5 mm (5). The smallest pedicle screws widely available are 3.5 mm in diameter, increasing the risk of pedicle screw excursion and necessitating the need for meticulous placement. In order to minimize risks of iatrogenic injury, accurate pedicle screw placement must be prioritized and accomplished in these spinal fusion procedures through precise guidance.

Traditionally, surgeons utilized free-hand fixation techniques when operating on scoliosis patients which relied on accurately locating physical landmarks to determine where to insert the screw, and this led to a wide range in accuracy of screw placement (3). This proved particularly difficult in deformity cases with small pedicles and complicated anatomy interfering with the surgeon’s view. In order to improve the accuracy of pedicle screw placement, fluoroscopic-assisted techniques were developed, yet these did not come without their own limitations such as increased operative time, radiation exposure, and instances of cortical perforation. However, studies do show that image-guided procedures have significantly lower rates of mechanical instrumentation-related complications, postoperative revisions, and unplanned readmissions (3). The O-arm, a portable CT-scanner which enables the use of image-guided navigation intraoperatively for instrumentation, has been shown to be accurate in visualizing pedicle screw position in the thoracic and lumbar spine, but it has less accuracy in the cervical spine. This may be because the cervical spine pedicles are smaller and more affected by artifact, as suggested by a human cadaveric study by Santos et al. (6). However, recent studies have also suggested that smaller pedicles such as those found in the cervical spine of adult patients or pedicles in children may be difficult to measure even with the O-arm and that surgeons may routinely miss instances of cortical breach, raising concern for late-effect iatrogenic injury (6,7). Our study seeks to support the current widely used practice of using intraoperative O-arm imaging during spinal fusion surgery for patients with AIS.

Therefore, the aims of this study are to (I) determine the accuracy of pedicle screws placed with intraoperative O-arm guidance at the thoracic and lumbar levels in spinal fusions for patients with AIS; (II) measure postoperative curvature correction and fusion maintenance; and (III) determine the reoperation rate and major complications for screw misplacement using O-arm guidance. We present this article in accordance with the STROBE reporting checklist (available at https://jss.amegroups.com/article/view/10.21037/jss-25-117/rc).

Methods

We conducted a retrospective review of all pediatric patients, aged of less than 18 years, undergoing posterior spinal instrumentation and fusion (PSIF) for AIS at the Department of Orthopedic Surgery at Maimonides Medical Center in Brooklyn, New York between June 2023 and August 2024 with a minimum of 2 weeks follow-up in office. AIS patients with Lenke 1AN–6C curve types and a pre-operative Cobb angle greater than 40° were studied (Figure 1). All surgeries followed a local navigation protocol via a two-step navigation process consisting of navigated pedicle probing and navigated pedicle screw placement. Patients underwent pre- and post-instrumentation intra-operative CT scans by O-arm to plan and confirm final screw position before primary closure (Figure 2). Postoperative imaging with X-rays were routinely collected at 5 weeks and 12 months following index surgery (Figure 3).

Figure 1 A pre-operative whole spine radiograph of a patient with adolescent idiopathic scoliosis (age: 12 years; sex: female; Cobb angle: 55.6°).

Figure 2 An intraoperative CT image of a pedicle screw placed without breach of the pedicle cortex (age: 13 years; sex: male). CT, computed tomography.

Figure 3 A post-operative whole spine radiograph of the patient from Figure 1 at the first follow-up visit (age: 12 years; sex: female; Cobb angle: 26.2°).

One researcher who was not involved in any of the surgeries evaluated all pedicle screws imaged via the Medtronic O-arm^TM Surgical Imaging System and graded the pedicle placement according to the Gertzbein and Robbins and Heary classifications in October 2025 (8,9). Screw placement was evaluated by determining cortical compromise by any portion of the screw (Figure 2). According to the Gertzbein and Robbins classification, each screw placement was assigned to one of five grades: Grade A = no breach of the pedicle cortex; Grade B = breaching the pedicle cortex <2 mm; Grade C = breaching the pedicle cortex 2–4 mm; Grade D = breaching the pedicle cortex 4–6 mm, or Grade E = breaching the pedicle cortex >6 mm or placement outside the pedicle (8). According to the Heary classification, each screw placement was also assigned to one of five grades: Grade I = completely contained within the pedicle; Grade II = breaches the lateral pedicle but the screw tip is completely contained within the vertebral body; Grade III = the screw tip breaches the anterior or lateral vertebral body; Grade IV = breaches the medial or inferior pedicle; or Grade V = breaches the pedicle or vertebral body, endangers neurological or vascular structures, and requires revision (9).

For each patient, the intra-operative blood loss (mL), total operative time (min), and pre-operative, post-operative, and follow up Cobb angles (°) were also recorded and a simple statistical analysis was performed. Any loss to follow up was analyzed with the patient’s available data. A review of all charts for instances of reoperation, major complications, and neurologic compromise due to screw misplacement was also performed.

Statistical analysis

All statistical analyses were conducted in R (R version 4.5.1) (10). A Wilcoxon Signed-Rank test was performed to compare pre-operative and post-operative Cobb angles. P<0.001 indicated a statistically significant difference.

Ethical considerations

The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the institutional review board of Maimonides Medical Center (No. IRB00000434) and individual consent for this retrospective analysis was waived.

Results

Accuracy of pedicle screw placement

A total of 227 pedicle screws were placed in 12 patients with AIS (4 males, 8 females; age range: 12–17 years; median age: 14 years) from June 2023 to August 2024. Of these 227 screws, the positions of 227 were considered Grade A according to the Gertzbein and Robbins classification and Grade I according to the Heary classification. These results show an accurate placement rate of 100% in our population (Figure 2).

Post-operative curvature correction and fusion maintenance

The mean pre-operative Cobb angle was 52.9° (n=12; range: 49.1–59.0°), the mean post-operative Cobb angle was 20.5° (n=12; range: 11.0–39.8°), and the mean follow-up Cobb angle was 19.8° (n=11; range: 6.4–41.3°) (Figures 1,3). One patient did not return for follow up after his or her post-operative visit. These results show a mean curvature correction of 33.1° (n=12; range: 8.5–49.8°) at the most recent visit. The results of our Wilcoxon Signed-Rank test showed a large, significant difference between the pre-operative Cobb angles (Mdn =51.5, n=12) and the post-operative Cobb angles (Mdn =19.7, n=12), (W+ =0, P<0.001, r=−1). The mean post-operative follow-up time was 5.25 weeks (n=12; range: 2–13 weeks), and the mean most recent follow-up time was 9.9 months (n=11; range: 1–13 months).

Reoperation rate and major complications

Among 12 patients with AIS, 0 patients required reoperation, resulting in a reoperation rate of 0%. Additionally, among these patients, 0 patients experienced a major complication, resulting in a major complication rate of 0%.

Discussion

We found an accurate placement rate of 100% in our population utilizing intraoperative O-arm acquired CT images. Furthermore, we found a mean curvature correction of 33.1° at postoperative follow up visits in addition to a 0% reoperation rate and a 0% major complication rate, and our Wilcoxon Signed-Rank test indicated a large significant effect of O-arm navigation-guided PSIF on Cobb angle. These findings show that intraoperative O-arm images are accurate in determining pedicle screw position in scoliosis surgery, and their utilization contributes to safe and effective correction of the spinal curve in patients with AIS. Pedicle screws are frequently utilized in the treatment of a variety of spinal disorders and deformities, particularly AIS (6). Their accurate placement in posterior scoliosis surgery is imperative in order to minimize the risk of serious neurovascular complications and to ensure both stable fixation in the bone and secure fixation of the spine (6,11). Intra-operative computer-assisted image guidance has been shown to successfully produce higher rates of accuracy in instrumented spine surgery (12,13). However, to the best of our knowledge no other study has been able to show that pedicle screw placement under CT-based navigation in spinal fusion surgery for patients with AIS also has such strong accuracy.

The findings of this study coincide with the results of other investigations. One study by Patil et al. assessed the accuracy of pedicle screw placement in 25 patients (188 screws) utilizing the O-arm/Stealth system and found that three screws (2.6%) breached the medial cortex and three screws (2.6%) did not follow the pilot hole trajectory (12). Another study by Conrads et al. retrospectively analyzed posterior instrumentation procedures performed in 285 patients (1,704 screws) in order to assess the accuracy of navigated, O-arm-controlled pedicle screw placement in thoracic and lumbar spine instabilities. They identified a high precision of screw positioning achieved in all spinal sections, with 1,621 screws (95.1%) showing excellent positioning. The lateral rim of the pedicle or vertebral body was breached in 25 (1.5%) and 28 (1.6%) screws, respectively. Intraoperative revision was performed for 78 screws and resulted in excellent positioning in 58 of them (14). The previously mentioned human cadaveric study by Santos et al. assessed the accuracy of intraoperative O-arm images in determining pedicle screw position and found that the overall accuracy for the thoracic and lumbar spine was 73% (6).

Of note, two studies concerned with pedicle screw placement in scoliosis specifically did not share such supportive findings. A prospective experimental study by Filezio et al. compared the accuracy of O-arm-acquired radiographic and CT evaluation of thoracic pedicle screw placement with open laminectomy in a simulation laboratory. In twenty simulation models of scoliosis from T3 to T7 and a total of 200 pedicle screws, they identified 48 breaches in the axial direct view after laminectomy, 18 of which were classified as unacceptable, and four breaches in the sagittal direct view, three of which were classified as unacceptable (7). Furthermore, Urbanski et al. compared the accuracy of intraoperative 3D image navigation against a freehand technique in 49 patients with idiopathic scoliosis undergoing posterior spinal fusion and found no differences between the two in terms of the proportion of screws that were properly positioned (96% freehand and 96% navigation; P=0.52). However, while this study did not find an increased accuracy compared to the freehand technique, its findings still demonstrate the accuracy of intraoperative O-arm navigation, with 374 out of 451 placed pedicle screws classified as having a Grade 0 breach and 58 having Grade 1 according to the Gertzbein and Robbins classification (11). This finding is in line with our own and those of much of the literature regarding pedicle screw placement in a variety of spinal surgeries: pedicle screw placement under navigation does provide a high degree of accuracy.

Our 0% major complication rate and 0% reoperation rate are also consistent with the results of other studies. A retrospective clinical study by Zhang et al. did not observe any direct intraoperative or postoperative complications caused by cervical pedicle screw placement, such as injury to the spinal cord, nerve root, or vertebral artery (15). A prospective single-center study by Åkerstedt et al. studied the agreement and accuracy of reviewers classifying pedicle screw placement in 70 patients who underwent instrumented thoracolumbar spine surgery with navigation. In addition, they similarly found that none of their patients developed any symptoms or complications resulting from screw malposition, and they further observed that no pedicle screws placed were revised or led to reoperation (13). Finally, in the study by Conrads et al., of 285 patients who underwent thoracic and lumbar spine surgery, only one required repeat surgery as a result of a missed pedicle screw malposition (14). These results support our own finding that O-arm navigation serves to improve the safety and success of pedicle screw placement.

The current study has some limitations. The first is the limited number of cases enrolled, owing to the low incidence of AIS. Future studies should seek to enroll more patients, but this study is strengthened by its significant number of pedicle screws analyzed [227]. Second, we did not compare the accuracy of screws placed under O-arm navigation to those placed without intraoperative navigation. However, at our hospital, the use of intraoperative navigation of screw placement is standard of care, so it was not possible for our spine surgeons to provide a control group without navigation. Finally, there is potential for measurement bias. As we had only one reviewer available to analyze each pedicle placement, the possibility of human error cannot be ignored. We attempted to decrease this bias by utilizing the Gertzbein and Robbins and Heary classifications in our analysis. These are popular classification systems used to assess the position of pedicle screws after spinal fixation, and we hope that by adhering to their criteria, we have limited this potential bias.

Conclusions

Intraoperative O-arm navigation offered a high level of precision for pedicle screw placement in AIS, a population characterized by severe spinal curvature and small, distorted pedicles. In this study, the use of O-arm guidance resulted in a 100% screw accuracy rate with no breaches, complications, or need for revision surgery. Postoperative radiographs confirmed meaningful deformity correction, which was sustained at intermediate follow-up. These findings underscore the value of advanced intraoperative imaging in enhancing both the safety and effectiveness of surgical treatment for complex pediatric spinal deformities. As technology becomes increasingly integrated into spine surgery, O-arm navigation should be considered an effective adjunct in AIS cases requiring reliable screw placement and optimal alignment outcomes.

Acknowledgments

None.

Footnote

Provenance and Peer Review: This article was commissioned by the Guest Editor (Ahmed K. Emara) for the series “Cost, Healthcare Utilization, Patient-Reported Outcomes and Technology in Modern Spine Surgery” published in Journal of Spine Surgery. The article has undergone external peer review.

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jss.amegroups.com/article/view/10.21037/jss-25-117/rc

Data Sharing Statement: Available at https://jss.amegroups.com/article/view/10.21037/jss-25-117/dss

Peer Review File: Available at https://jss.amegroups.com/article/view/10.21037/jss-25-117/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jss.amegroups.com/article/view/10.21037/jss-25-117/coif). The series “Cost, Healthcare Utilization, Patient-Reported Outcomes and Technology in Modern Spine Surgery” was commissioned by the editorial office without any funding or sponsorship. M.K.N. has received consulting fees from Stryker, Johnson and Johnson Ethicon, Pacira BioSciences Inc., Sage Products Inc., Bonutti Technologies Inc., Alafair Biosciences Inc., Next Science LLC, CurvaFix Inc., Hippocrates Opportunities Fund LLC, and Ferghana Partners Inc. The authors have no other conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the institutional review board of Maimonides Medical Center (No. IRB00000434) and individual consent for this retrospective analysis was waived.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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