Paper template–based intraoperative rod bending for percutaneous stabilization of thoracic extension-distraction fracture: illustrative case

Abstract

BACKGROUND

Distraction fractures are unstable spinal injuries characterized by a horizontal fracture line through the vertebra, often occurring following deceleration mechanisms. Surgical management typically involves fixation and fusion to restore sagittal alignment. Minimally invasive approaches, including percutaneous pedicle screw fixation, have demonstrated reduced operative morbidity while achieving deformity correction comparable to that of open techniques. However, accurate rod contouring in percutaneous procedures remains technically challenging.

OBSERVATIONS

A 61-year-old male presented with a three-column unstable T7 distraction fracture in the setting of diffuse idiopathic skeletal hyperostosis following a rear-end motor vehicle accident at low to moderate speeds. A T4–10 percutaneous pedicle screw fixation for fracture reduction and stabilization was performed. Preoperative CT images were formatted and printed at a 1:1 scale on a sheet of paper; cut along the fracture line, taped together to reduce the fracture, and photocopied; sterilely bagged; and used intraoperatively to guide rod bending prior to placement.

LESSONS

Using a 1:1 ratio paper printout of the patient’s preoperative CT scan as an anatomical template, the authors appropriately performed intraoperative rod bending without additional adjustment of rod contour. This method offers a practical, cost-effective solution to improve the precision and efficiency of rod bending in percutaneous spinal fusion.

https://thejns.org/doi/10.3171/CASE26257

Traumatic fractures of the spine represent a common indication for spine surgery, with the thoracolumbar junction (T10–L2) especially vulnerable to injury due to the biomechanical stress carried between the mobile lumbar spine and the relatively rigid thoracic spine.^1,2 Distraction fracture is a distinct subset of unstable spine fractures often characterized by a horizontal fracture line through the spinous process, laminae, transverse processes, and pedicles and into the vertebral body due to flexion-distraction forces.³ Frequently following rapid deceleration in motor vehicle accidents, where the spine flexes over the lap seat belt, distraction injuries have accounted for 7.2% of indications for radiographic evaluation of the vertebrae in blunt trauma patients.^4,5 Although they can be overlooked on clinical examinations due to the lack of accompanying neurological deficits, early diagnosis and treatment of distraction fractures are crucial to optimizing prognosis and outcome.⁴

Surgical management of distraction fractures involves fixation and fusion, with long- and short-segment stabilization resulting in improved sagittal alignment and functional recovery.⁶ Long-segment instrumentation could provide increased long-term stability by distributing corrective force over a greater number of segments, while restricting instrumentation to the fractured level may reduce unnecessary motion segment loss.^6–8 Minimally invasive techniques, such as percutaneous pedicle screw fixation, are valuable treatment options for patients with thoracolumbar fractures due to their association with decreased operative time, hospital stay, and blood loss.^3,7,9,10 Demonstrating similar efficacy in the correction of traumatic malalignment to open procedures, percutaneous fixation has provided adequate sagittal balance and long-term outcomes.^3,7,9,10

Rod bending has been incorporated into percutaneous fixation to preserve normal spinal curvature at the level of the fractured vertebra and the overlying disc.¹¹ Strategies for rod bending include prebending of the rods prior to implantation and in situ rod contouring on the spine.^11–14 Nevertheless, accurate rod bending remains a technical challenge, especially for multilevel fusion constructs.¹⁴ We present the successful reduction of a three-column distraction fracture of the T7 vertebra with rod bending using a 1:1 ratio paper printout of the preoperative CT scan for the percutaneous stabilization, illustrating the utility of such a method for achieving appropriate rod contouring.

Illustrative Case

History and Imaging

A 61-year-old male with a history of stroke, prediabetes, and gout was transferred to the emergency department of our hospital from his previous hospital for trauma reevaluation. He arrived at his previous hospital by ambulance with thoracic back pain following a rear-end motor vehicle collision with an estimated vehicle speed of 25 to 50 mph. He was wearing a seatbelt with no airbag deployment. Physical examination findings were unremarkable, including a Glasgow Coma Scale score of 15 and a National Institutes of Health Stroke Scale score of 0. CT imaging of the thoracic spine demonstrated an acute T7 fracture with separation of the superior endplate from the vertebral body and mild adjacent hematoma, which prompted the transfer to our hospital.

On arrival at our hospital, he described midline thoracic pain, ranging from 3 of 10 at baseline up to 7–8 of 10 with movement. He denied any symptoms concerning for acute neurological injury, such as saddle anesthesia, bowel or bladder dysfunction, nausea, vomiting, or other motor or sensory deficits. CT of the thoracic spine was performed, which revealed a three-column unstable fracture at T7 with approximately 10.7 mm of separation of the anterior superior endplate of the vertebral body in the setting of diffuse idiopathic skeletal hyperostosis (DISH) (Fig. 1).

FIG. 1.

Sagittal CT scan of the thoracic spine demonstrating an acute three-column unstable fracture involving the anterior superior endplate of the T7 vertebral body. The T7 vertebral body fracture was 10.7 mm distracted. The horizontal fracture line extends through the vertebral body to the posterior elements, suggesting a flexion-­distraction injury. No retropulsion into the spinal canal is noted.

Rod Bending and Percutaneous Fusion

Given that the patient was neurologically intact, surgery was recommended to stabilize the spine and preserve neurological function. A unique consideration in this patient’s plan was that he had long lever arms above and below the fracture level, a result of DISH. Therefore, the incorporation of three vertebral segments above and below the fracture was chosen, as opposed to two.¹⁵ Fusion of the T4–6 or T8–10 levels was unnecessary, as the segments were already fused in the setting of DISH. Therefore, an open surgery to decorticate the lamina, facet joints, and spinous processes of T4–10 was not indicated, which might also lead to increased blood loss and time to recovery. However, an appropriate angulation of the rods for the percutaneous fixation was necessary so that the fractured T7 vertebral body could join in an anatomical configuration and fuse together. After a thorough discussion of risks, benefits, and alternatives, the patient elected to proceed with the surgical plan.

Because of the operation being percutaneous as opposed to open, the location of the pedicle screw tulip heads would be difficult to visualize, creating a challenge for proper rod contouring. Various rod bending strategies were therefore considered to ensure appropriate seating of the rods within the tulip heads. Computer-assisted rod bending systems, such as Bendini (NuVasive), can estimate rod trajectory based on tulip head positions and produce a contoured rod of appropriate length for percutaneous placement.¹⁶ However, use of such a system would add to the cost of the operation. Additionally, such a system may not be readily available at all medical centers and is often limited to use with a specific implant manufacturer. Moreover, rods contoured using such a system would not necessarily reduce the distracted fracture.

Alternatively, we used the patient’s preoperative CT imaging as a template for rod bending. To create the template, we selected a sagittal thoracic CT slice that involved the pedicles. A screenshot of this image was captured directly from the PACS viewer with a ruler overlaid on the screen to preserve the on-screen distance measurement scale (e.g., the built-in digital CT ruler/measurement marker shown in millimeters). The screenshot was then printed on paper and resized so that the digital marker exactly matched the corresponding length measured with a physical ruler (e.g., the 100-mm reference line measured 100 mm on paper). Once the 1:1 scale was confirmed, the printed image was trimmed, and the two broken pieces of T7 were angled so that the fractured edges closed down, approximating anatomical reduction. The finalized template was produced by sending the properly formatted CT scan through a copy machine (Fig. 2). The entire process took about 5 minutes and incurred negligible cost.

FIG. 2.

Creation of the paper template using the patient’s preoperative CT images printed on paper. A:Before scale adjustment. B: After scale adjustment to achieve 1:1 scale based on the 100-mm reference marker. C: After trimming and taping the cut image to approximate fracture reduction. D: After reproduction using a copy machine with estimated tulip head positions marked. E: After placement in a sterile bag to guide intraoperative rod sizing and bending. The template preparation process was recreated for publication purposes, with steps shown reflecting the exact method used in this case.

The paper template was sterilely placed in a bag and brought into the operative field to assist with rod bending. The patient’s reference frame was secured to the T2 spinous process for percutaneous placement of pedicle screws at T4–6 and T8–10 under neuronavigation. The appropriately bent rods were then inserted subfascially through the screw towers and held in place within the tulip heads (Fig. 3). After fluoroscopic confirmation of the successfully reduced distraction fracture at T7 with the properly contoured rods, final tightening was performed with countertorques, followed by removal of the towers (Fig. 4).

FIG. 3.

Intraoperative radiographs of the thoracic spine. A: Anteroposterior radiograph obtained after patient positioning to approximate the location of the spinous process clamp for the O-arm. B and C: Lateral radiographs obtained after rod insertion through the screw towers but before set cap tightening, demonstrating the construct at T4–6 (B) and T8–10 (C) with the rod held within the tulip heads. The set caps for the middle pedicle screws were used to increase the kyphosis across the fractured vertebral body, as seen in the gap between the rod and the tulip heads.

FIG. 4.

Intraoperative photographs. A: Placement of pedicle screws over T4–6 and T8–10, followed by percutaneous insertion of appropriately bent rods. B: Rod bending using the paper template.

Outcome

The patient recovered well without neurological deficits or focal weakness. He denied signs of saddle anesthesia, bowel or bladder dysfunction, or problems with fine motor control. Postoperative radiographs showed well-maintained sagittal alignment without screw pullout. The 10.7-mm distraction of the T7 vertebral body fracture observed before surgery was successfully reduced to 0 mm (Fig. 5). He continued to wear a thoracolumbar spine orthosis. At the 2-month follow-up, the patient was able to perform all activities of daily living without assistance.

FIG. 5.

Postoperative radiographs of the thoracic spine. A: Anteroposterior radiograph demonstrating intact hardware. B: Lateral radiograph demonstrating successful reduction of the T7 distraction fracture to 0 mm.

Informed Consent

The necessary informed consent was obtained in this study.

Discussion

We present a case of a T7 three-column distraction fracture treated with percutaneous fusion with the use of a printout of the patient’s preoperative CT scan as a paper template for intraoperative rod bending. Proper rod bending has been shown to enhance restoration of sagittal balance in spinal fusion, while adequate rod curvature can contribute to better surgical outcomes.¹⁷ However, freehand rod bending remains a technical challenge, and extensive reviews have revealed the inconsistency and variability in rod bending, resulting in misaligned rods and increased risk of hardware failure.^14,18 Although adjustments of rod contour can be made following rod placement, in situ reduction of rod misalignment can affect the rotation of motion segments, induce high joint loading, and increase the strains in adjacent spinal segments.¹⁹ Appropriate rod bending with minimized rebends is preferred to reduce the risk of rod fracture or screw loosening. Therefore, we propose the use of a printout of the formatted preoperative CT scan that provides 1:1 comparison to the spine to assist with intraoperative rod bending.

Observations

Rod bending has long been incorporated in instrumented spinal fusions for the surgical correction of spinal deformities.¹⁴ Owing to the unstable nature of distraction fractures, the literature has largely recommended surgical stabilization over conservative management for the improved kyphosis, pain, and functional outcomes achieved by surgical management, with pedicle screw fixation being a well-­established technique for treating distraction fractures.^6,20 During pedicle screw fixation for the reduction of thoracolumbar distraction fractures, surgeons may incorporate rod bending to restore and maintain the physiological curvature of the spine.²⁰ Rod bending can be performed under direct visualization of the anatomy in traditional open procedures, allowing fine in situ manipulation of hardware for optimal rod-screw conformity. On the other hand, percutaneous pedicle screw fixation poses additional challenges to the surgeon by limiting both visualization and working fields. Since the location of the tulip heads may not be visible, achieving appropriate rod contour may require multiple trial-and-error attempts at rod passage and removal, while repeated rebending can introduce residual stress, compromise the mechanical integrity of the rods, prolong operative time, and increase the risk of complications.^14,21

Rod bending is susceptible to surgeon-dependent variability, including differences in bending technique, visual-spatial judgment, and estimation of springback compensation, which may lead to a mismatch between the intended and actual contour of the fused segment and an unpredictable residual stress distribution within the construct.^14,22–24 To address the variability and inadequacy of rod manipulation techniques, several strategies have been proposed and tested. One approach is to use reference templates for rod bending. Two-dimensional metallic templates bent to selected angles have been shown to aid manual rod bending in achieving target angles.²² A 3D-printed moulage designed based on the 3D reconstruction of the patient’s CT scan significantly improved the accuracy of rod bending compared to freehand bending without the moulage.²⁵ A 1:1 ratio 3D-printed spine model of the instrumented vertebrae and pedicle screw head tulips allowed preoperative cutting and bending of rods that were later autoclaved for intraoperative use, and no adjustments of rod contour or length were made after percutaneous insertion.²⁶

Besides template-guided rod bending, augmented reality and computer-assisted technologies have been developed to overcome the technical challenges of freehand rod bending. Recent innovations in automated rod bending using augmented reality and robotics allowed the reduction of per-screw tensile/compressive residual stress and instrumentation time, while improving inter- and intrasurgeon consistency.²⁷ Intraoperative use of augmented reality technology also increased the precision of rod bending while decreasing the number of in situ checks, rod length corrections, and radiographic verifications compared to freehand techniques.²⁸ Computer-assisted rod bending balanced the precision of automated shaping systems and the flexibility of manual bending by instructing rod bending via an algorithm-generated protocol, with surgeons using a custom-designed tool.¹⁸ In a retrospective comparative study, the computer-assisted rod bending system significantly reduced screw pullout and loosening, leading to improved postoperative low back pain compared to manual rod bending.²⁹

Nonetheless, prebent rod systems designed for adolescent idiopathic scoliosis (AIS) facilitated standardized rod bending during posterior spinal surgeries for AIS patients.³⁰ Representative rod shapes were identified from previously treated patients and could be used in corrective surgeries for AIS without additional rod contouring.³⁰ Four-dimensional anatomical spinal reconstruction that calculated the postoperative apex of thoracic kyphosis could further assist with producing notch-free, prebent rods for AIS surgery.^31,32

We introduce a rod bending technique guided by a 1:1 scale printout of the patient’s preoperative CT scan, which replicates the spinal anatomy. In our patient, CT-guided, appropriately bent rods successfully reduced the distraction fracture of the T7 vertebra. No rebends were performed following rod installation, ensuring minimal mechanical stress within the fusion construct. We explored the benefits of using a template, producing a cost-effective option that facilitated proper intraoperative rod contouring without requiring extensive preoperative preparation or advanced technologies. Our method addressed the limitations of percutaneous procedures and enabled direct visualization of the patient’s anatomy during rod bending, using printed CT images as a reference.

Lessons

We present a case of a three-column T7 distraction fracture reduced with percutaneous stabilization, using a 1:1 printout of the preoperative CT scan as a paper template to assist with rod bending. Despite the benefit of rod contouring in enhancing postoperative sagittal realignment, the paucity of standardized methods for achieving precise rod shapes limits the accuracy of manual rod bending. Referencing a printed CT scan depicting the patient’s anatomy at 1:1 scale may be a beneficial method for efficiently promoting accurate rod bending without being technologically demanding.

This approach may be subject to limitations. As manual rod bending is still required, the quality of bent rods may still depend on the surgeon’s experience and familiarity with rod bending. Furthermore, the printed preoperative CT scan must accurately capture the patient’s anatomy, and its utility would be compromised if there exists a mismatch between the printed image and the patient’s actual spinal curvature. Nevertheless, the use of a printed CT scan to guide intraoperative rod bending is a feasible approach to improving the accuracy and efficiency of rod bending, ensuring the production of mechanically favorable constructs in percutaneous spinal fusion.

Disclosures

N. Bhatia reported personal fees from Alphatec, Spineart, Lifespine, Orthofix, and Aurora spine outside the submitted work. D. Park reported personal fees from Globus, TrackX, and Elliquence; grants from Amplify Surgical; and royalties from Alphatec and SeaSpine outside the submitted work.

Author Contributions

Conception and design: Jin, Lopez, Bhatia, Wu, Bow. Acquisition of data: Jin, Lopez, Bhatia, Bow. Analysis and interpretation of data: Jin, Lopez, Bhatia, Lee, Mills, Bow. Drafting the article: Jin, Lopez, Bhatia, Lee. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Jin. Administrative/technical/material support: Lopez. Study supervision: Hashmi, Wu.

Correspondence

Haiyue Jin: University of California, Irvine, Orange, CA. haiyuej1@hs.uci.edu.