How good are we at rod bending?—a review of the literature and a case series of experienced pediatric and adult scoliosis surgeons

Introduction

Low back pain affects more than 577 million people globally (1). When conservative treatments fail, corrective spinal fusion becomes a preferred surgical intervention, particularly for conditions such as scoliosis, kyphosis, and spinal stenosis. In the US alone, approximately 1.62 million instrumented spinal surgeries are performed annually (2). Even with many conservative treatments and potential surgical interventions, back pain is still the leading cause of worldwide disability (3). Surgical management for debilitating deformity is often required. The success of corrective spinal fusion surgery hinges on two key components: precise placement of pedicle screws and accurate rod bending to align with the screws, ensuring inter-vertebral immobility and pain relief (4). However, manual rod contouring is challenging. Inaccurate rod shapes increase stress at the screw-bone interface, leading to complications such as screw loosening and rod breakage rates as high as 4.2% in some populations, often necessitating revision surgeries (5,6). The pull-out resistance of loosened screws diminishes significantly, exacerbating this issue in multilevel fusions and areas of high local stress (7,8). Prolonged surgery time, linked to such complexities, also increases costs, blood loss, and infection risks, highlighting the need for more standardized and precise rod contouring methods (9,10).

Technological advancements have improved pedicle screw placement through navigation systems, augmented reality (AR), and robotics. Recent advances in robotic-assisted spinal surgery have improved precision in screw placement and reduced manual bending time, offering potential advantages in surgical efficiency and alignment outcomes (11). AR-guided rod bending reduces bending time and maneuvers but still relies on the surgeon’s skill (11). Stereo neural networks for screw positioning further enhance precision, suggesting minimal human influence could improve outcomes (12,13). Yet, the rod bending process remains largely unexplored and dependent on the surgeon’s dexterity.

Intraoperative changes in rod geometry, particularly during scoliosis surgery, introduce further complexities in achieving the desired spinal alignment. Significant deformation of the rod has been observed during these procedures, which suggests that maintaining the intended rod shape requires continuous, precise adjustments throughout surgery (14). These challenges underscore the importance of careful rod manipulation to ensure that the final rod configuration matches the surgical plan and effectively corrects the spinal deformity. Pre-bent rods, designed based on predefined geometries, have been shown to reduce operation time and improve clinical outcomes by eliminating the need for manual intraoperative rod contouring (15). However, caution is advised when using pre-bent rods, as they unwanted plastic deformation compared to manually bent rods, which can better maintain curve correction over time (16).

Further research into biomechanical implications shows that rod materials and contouring techniques significantly affect rod strength and fatigue life. For instance, rod contouring with a French Bender reduces the fatigue life of titanium spinal constructs, suggesting a need for improved methods to enhance durability (17,18). Additionally, preoperative planning tools, like 3D stereoradiography, aid in achieving more accurate rod shapes and better surgical outcomes (12). Patient-specific rods (PSRs) promise to transform preoperative planning into postoperative reality, enhancing surgical outcomes by precisely matching the patient’s anatomical requirements (19-21). The potential for AR-based navigation to deliver accurate, operator-independent results in pedicle screw placement and rod bending supports further integration of advanced technologies in spinal surgery (22).

Despite these advancements, some gaps remain in the literature regarding the tools, number of bends, and cuts surgeons use to achieve the desired rod shape. While many efforts have been made to improve techniques in spine surgery, there is a surprising lack of data regarding baseline bending maneuvers, cutting attempts, and the time it takes to shape a rod. This study is valuable for gathering information needed to inform future innovations and enhance surgical precision. The purpose of this case series was to investigate the intraoperative process of spinal rod cutting and bending, focusing on the number of attempts and maneuvers required to achieve the desired rod configuration. By identifying common challenges and quantifying the effort involved, this study aims to provide insights that can lead to the development of more efficient techniques and tools for spinal rod manipulation. This information will serve as a baseline for future studies exploring rod bending and cutting in greater detail, particularly those performed by fellowship-trained spine surgeons. We present this case series in accordance with the AME Case Series reporting checklist (available at https://jss.amegroups.com/article/view/10.21037/jss-24-113/rc).

Case presentation

Ethical statement

The study was conducted with the approval of the Institutional Review Board (IRB) at the Cleveland Clinic Foundation (IRB #24-371). This study was conducted in compliance with all relevant ethical standards and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patients or their legal guardians for publication of this case series and accompanying images. A copy of the written consent is available for review by the editorial office of this journal. All patient data were treated as confidential according to Health Insurance Portability and Accountability Act standards. Any protocol amendments were submitted to the IRB for review and approval.

Materials and methods

The study was a minimal risk prospective observational study conducted during May–June 2024. The primary aim was to assess the surgical rod cutting techniques in adult and pediatric spinal surgeries, focusing on the time required for the process, the number of attempts and bending maneuvers, potential contamination events, and a qualitative evaluation of the rod measuring method.

Study design

The study included nine patients and 18 rods used across both adults and pediatric patients undergoing surgeries involving rod insertion. The inclusion criteria were broad to ensure generalizability: all adult and pediatric patients undergoing any surgery involving rod insertion. Exclusion criteria were patients receiving pre-cut or pre-bent rods and those undergoing spine surgery without rod insertion.

The observer was present in the operating room during the rod cutting procedure and documented various parameters, including the time from initial rod measurement to final insertion, the number of rod cuts, bending maneuvers, any contamination events, and a qualitative description of the rod measuring method. The type of rod used was also recorded.

Demographics

Demographic data for each patient, including age, gender, and type of surgery (adult or pediatric), were collected.

Patient population or clinical outcomes

The primary outcomes measured practical aspects and results of the rod cutting procedure. Parameters recorded included the time required for rod cutting, the number of attempts and bending maneuvers, contamination events, and a qualitative assessment of the measuring method used. The data was averaged to determine the typical number of attempts and maneuvers.

Data collection and management

Data were input into the institutional REDCap system. Only password-protected secure computers on the Main Campus were used for data analysis and retrieval. The data were stored securely in REDCap and accessible only to research personnel. If data needed to be transported, IRONKeys were used. No Cleveland Clinic Foundation data were shared with any outside institution.

Statistical analysis

The data were analyzed with the support of biostatisticians from the Qualitative Health Sciences associated with the Orthopaedic and Rheumatologic Institute. Descriptive statistics were the primary mode of presenting evidence. As the study was prospective and did not include comparison data, the focus was on averaging the number of attempts and maneuvers. Continues variables were summarized by median and interquartile range (IQR), and categorical variables were reported using counts and percentages. The analysis was performed using R (4.3.1).

Study oversight

The principal investigator (Dr. R.G.), co-investigators (Dr. O.F.), and coordinator (K.O.) oversaw the study. Dr. O.F. was responsible for the overall study conduct, data integrity, and protocol compliance.

Surgical rod characteristics

As seen in Table 1, this study evaluated 18 rods used across spinal surgeries. Titanium rods were used in 66.7% of cases (n=12), while cobalt chromium rods accounted for the remaining 33.3% (n=6). Most rods (44.4%) were supplied by Stryker, followed by Globus and Everest (11.1% each), with 33.3% of cases having unspecified suppliers. Rod diameters were primarily 6 mm (77.8%), with 5.5 mm used in 11.1% of cases. The initial rod lengths varied, with 500 mm being most common (33.3%), followed by 600 mm (22.2%) and 450 mm (11.1%). For 33.3% of cases, the initial rod length was not recorded.

Rod measuring method

As seen in Table 2, the methods for rod measurement varied, with the Bovie cord being the most frequently used method (33.3%), followed by the malleable rod and suture string (11.1% each). In 33.3% of cases, no specific measurement method was recorded.

Intraoperative rod manipulation data

Table 3 shows the intraoperative rod manipulation data. The average rod manipulation time was 20.0 minutes, with a minimum of 13.0 minutes and a maximum of 29.0 minutes. The number of rod cuts ranged from 0 to 3, with the majority of cases (66.7%) requiring two cuts. The average number of ex-situ rod bends ± standard deviation (SD) was 4.22±4.24, while in-situ bends averaged 0.89±1.17. Importantly, no contamination events were recorded across all procedures.

The primary tools used for rod manipulation included the table top cutter and French rod bender, each used in 77.8% of cases. In-situ benders were employed in 44.4% of cases, while heavy rod holders were used in 22.2% of cases. No instances of dural tear, vascular injury, or spinal cord injury were observed during the procedures.

Rod manipulation analysis by rod characteristics

• Rod type, represented in Table 4: titanium rods required an average of 2.33 ex-situ bends and 1.33 in-situ bends, while cobalt chromium rods required more manipulation, with an average of 8.00 ex-situ bends and no in-situ bends. The manipulation time was comparable between titanium and cobalt chromium rods, with times of 26.8 and 24.7 minutes, respectively.

  Table 4

  Rod type (n=18)

  
  

  Variables	All (n=18)	Rod type
  		Cobalt chromium (n=6)	Titanium (n=12)
  Average number in-situ bends	0.89±1.13	0.00±0.00	1.33±1.15
  Average number ex-situ bends	4.22±4.11	8.00±3.90	2.33±2.74
  Rod manipulation time (min)	26.1±21.6	24.7±4.03	26.8±26.7

  Data are presented as mean ± SD. SD, standard deviation.
• Rod measuring method, represented in Table 5: the Bovie cord, which was used in three cases, had an average manipulation time of 28.0 minutes with 7.33 ex-situ bends and 1.00 in-situ bends. Cases where no specific method was recorded had the shortest average manipulation time at 13.3 minutes.

  Table 5

  Rod measuring method (n=9)

  
  

  Variables	All (n=9)	Rod measuring method
  		Old rod (n=1)	Piece of suture string (n=1)	Bovie cord (n=3)	Malleable rod (n=1)	None used (n=3)
  Average number in-situ bends	0.89±1.17	1.00	2.00	1.00±1.73	2.00	0.00±0.00
  Average number ex-situ bends	4.22±4.24	2.00	1.00	7.33±5.51	8.00	1.67±1.53
  Rod manipulation time (min)	26.1±22.3	13.0	18.0	28.0±7.55	80.0	13.3±10.4

  Data are presented as mean ± SD. Data without SD value indicate the only observed value because n=1. SD, standard deviation.
• Initial rod length, represented in Table 6: rods with an initial length of 500 mm required the longest manipulation time (41.7 minutes) and the highest number of ex-situ bends (7.33). Rods with unspecified initial lengths had an average manipulation time of 9.33 minutes and required the least amount of bending.

  Table 6

  Initial rod length (n=9)

  
  

  Variables	All (n=9)	Initial rod length (mm)
  		Not recorded (n=3)	450 (n=1)	500 (n=3)	600 (n=2)
  Average number in-situ bends	0.89±1.17	0.33±0.58	2.00	0.67±1.15	1.50±2.12
  Average number ex-situ bends	4.22±4.24	1.33±1.15	1.00	7.33±4.04	5.50±6.36
  Rod manipulation time (min)	26.1±22.3	9.33±4.04	18.0	41.7±33.3	32.0±4.24

  Data are presented as mean ± SD. Data without SD value indicate the only observed value because n=1. SD, standard deviation.

Figures and visual representation

Figures 1-3 present a visual summary of rod characteristics, measuring methods, and manipulation data, respectively, providing a graphical comparison of the manipulation times, bend counts, and other parameters across various rod characteristics.

Figure 1 Comparison of rod types: manipulation time and bending attempts (in and out of spine).

Figure 2 Comparison of rod measuring method: manipulation time and bending attempts (in and out of spine).

Figure 3 Comparison of initial rod length: manipulation time and bending attempts (in and out of spine).

Discussion

The manual contouring of spinal rods during surgery poses significant challenges, largely due to the subjective nature of the process and its reliance on the surgeon’s experience and dexterity. These challenges have long been recognized as key factors influencing the success of corrective spinal fusion procedures, particularly in preventing complications such as screw loosening and rod breakage (4,11). Despite advancements in preoperative planning and surgical technologies, variability in rod bending techniques remains a concern. This study addresses notable gaps in the literature by providing data on the actual intraoperative details of rod bending and cutting maneuvers, time expended, and tools used. This information is vital for future innovations aimed at improving the precision of spinal rod manipulation during surgery.

The findings from this study, based on 18 spinal rods, provided valuable insights into rod manipulation times, bending techniques, and the influence of rod characteristics such as material and length. The average time spent on rod manipulation was 20.0 minutes, ranging from 13.0 to 29.0 minutes. The number of rod cuts per case ranged from 0 to 3, with most cases requiring two cuts (66.7%). Titanium rods required fewer ex-situ bends (2.33) compared to cobalt chromium rods (8.00), reflecting potential differences in material flexibility. Measurement methods, such as the use of the Bovie cord, were associated with longer manipulation times (28.0 minutes), though the small sample size limits definitive conclusions. Rods with longer initial lengths (500 mm) appeared to require more ex-situ bends (7.33), highlighting the importance of efficient measurement and manipulation tools. While the absence of contamination events is reassuring, these findings underscore the variability in current techniques and suggest opportunities for improving efficiency and consistency in rod preparation.

While this study excluded patients with pre-bent rods, future investigations should include comparative analyses of intraoperative manipulation versus pre-bent rod use to assess cost-efficiency and surgical outcomes. Measuring tools further complicate the process. In some cases, methods like using suture string to measure rod length were employed, which can be inefficient and waste operating room resources. Moreover, smooth, minimal attempts at rod bending are essential, as repeated manipulations can lead to notching which compromises rod integrity and increases the likelihood of mechanical failure. These findings emphasize the significant impact that current practices can have on surgical efficiency and patient safety, highlighting the need for improved techniques and tools.

Comparing this study with existing literature, we see that while the challenges of rod bending are documented, they are not adequately quantified. Studies have highlighted the mechanical vulnerabilities introduced by manual rod contouring, such as reduced fatigue life and yield strength in contoured rods (17,18). However, these studies focus on post-contouring rod properties rather than the intraoperative processes leading to these outcomes. This study complements those findings by detailing the manipulations required, time taken, and methods used, which are important yet often overlooked factors in surgical planning.

The time required for rod manipulation, as observed in this study, underscores the need for more efficient methods to reduce operative time. Longer surgeries are directly correlated with increased risks, such as greater blood loss and higher infection rates (9,10). Understanding the inefficiencies and time-consuming aspects of current rod bending practices is essential for developing solutions to improve surgical efficiency and outcomes.

These findings may inform the development of new technologies and methods that reduce variability in rod bending. AR and robotics have shown promise in improving the accuracy of rod bending, thereby reducing reliance on individual surgeon skill (11,22). However, adopting such technologies may face challenges due to their complexity and the need for significant infrastructure and training. The data from this study could guide research into simpler, more adaptable tools that improve rod insertion metrics and integrate easily into current surgical practices.

This study has limitations. The small sample size and focus on experienced surgeons may limit the generalizability of the findings. Additionally, while pre-bent rods were excluded from the study, future research should compare intraoperative manipulation with pre-bent rod use to assess differences in cost-efficiency, time, and surgical outcomes. The small sample size also limits the statistical power for comparative analysis, reducing the ability to draw firm conclusions from subgroup data. Furthermore, the observational nature of the study does not directly address long-term patient outcomes, such as rod breakage or screw loosening. Finally, variability in surgical contexts, such as differences in rod lengths and materials, may introduce confounding factors that were not fully explored in this analysis. Future studies should aim to include larger, more diverse patient populations and examine long-term clinical outcomes. This case highlights how rod contouring needs can vary based on specific surgical contexts, and future studies should account for this variability in their design.

Conclusions

This study provides valuable data on the intraoperative practices of rod cutting and bending in spinal surgery. This study’s primary strength is that it sets a framework for identifying which parameters should be consistently collected and compared in future research. Establishing baseline data on the number of rod bending and cutting maneuvers, time involved, and tools used will allow future studies to explore correlations with clinical outcomes and optimize surgical techniques. The findings highlight the variability in current techniques and underscore the need for more standardized methods. While technologies such as AR and robotics hold promise for improving surgical outcomes, they may face difficulties in widespread adoption. The data gathered in this study could guide research toward simpler, more adaptable solutions that integrate easily into surgical workflows. To address the variability and inefficiency in current rod manipulation techniques, surgeons might consider utilizing standardized tools and techniques, such as pre-operative planning software that customizes rod contours based on patient-specific anatomy and anticipated corrections. Additionally, AR guidance could facilitate real-time visualization and adjustment, potentially reducing reliance on trial-and-error adjustments and minimizing manipulation time. Implementing these approaches could streamline intraoperative processes, enhance accuracy, and ultimately improve patient outcomes. Based on these results, we recommend further research into developing easy-to-use tools that enhance accuracy, efficiency, and overall success in rod insertion during spinal surgeries.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the AME Case Series reporting checklist. Available at https://jss.amegroups.com/article/view/10.21037/jss-24-113/rc

Peer Review File: Available at https://jss.amegroups.com/article/view/10.21037/jss-24-113/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-24-113/coif). E.W. has done direct consulting with Precision Medical Products on other projects not related to this publication and has stock in Orthofix Medical Inc. from his previous employment with them. R.G. received consulting fees (individual) from Stryker Spine and Highridge Medical. The other authors have no 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 with the approval of the Institutional Review Board (IRB) at the Cleveland Clinic Foundation (IRB #24-371). All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patients or their legal guardians for publication of this case series and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

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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