Summary
Herein, we present a three-dimensional printing guide template for percutaneous vertebraplasty. A patient with a T11 vertebral compression fracture was selected as a case study.
Abstract
Percutaneous vertebroplasty (PVP) is considered an effective treatment for the back pain caused by osteoporotic vertebral compression fracture. The accuracy of PVP mainly depends on the surgeons' experience and multiple fluoroscopes during a traditional procedure. Puncture related complications were reported all over the world. To make the surgical procedure more precise and decrease the rate of puncture-related complications, our team applied a three-dimensional printing guide template to PVP to modify the traditional procedure. This protocol introduces how to model target vertebrae DICOM imaging data into three-dimensions in the software, how to simulate operation in this 3-D model, and how to use all of the surgical data to reconstruct a patient specific template for application. Using this template, surgeons can identify suitable puncture points accurately to improve the accuracy of the operation. The whole protocol includes: 1) diagnosis of the osteoporotic vertebral compression fracture; 2) acquisition of CT imaging of the target vertebra; 3) simulation of the operation in the software; 4) design and fabrication of the 3-D printing guide template; and 5) application of the template into an operation procedure.
Introduction
As the most common type fracture among all kinds of osteoporotic fractures, osteoporotic vertebral compression fracture (OVCF) is a highly concerning clinical problem nowadays. As current guidelines recommend, percutaneous vertebroplasty is one of the most effective minimally invasive methods to clinically treat osteoporotic vertebral compression fractures1.
Traditionally, surgeons perform percutaneous vertebroplasty guided by a C-arm fluoroscope to treat a vertebral compression fracture to restore the compressed vertebral body and relieve early-stage pain2. Even experienced surgeons make mistakes in confirming suitable puncturing points by simply relying on their personal experience. This operation could cause some puncture-related complications (e.g., cement leakage into surrounding tissues, nerve root injury, intra-spinal hematoma, etc.3,4,5); moreover, almost 50% of patients have local complications from traditional PVP with 95% of complications coming from cement leakage into surrounding tissue or embolization of paravertebral veins6. With the emergence of precision surgery, a 3-D printing guide template has been used in many spinal surgery operations7 because it can enhance the procedural accuracy, decreasing the difficulties and minimizing the operational risks. Here, we apply a 3-D printing guide template into the PVP to make the surgical procedure more precise and to decrease the rate of puncture-related complications. Compared with the traditional method, operations assisted by the 3D printing guide template have 1) increased surgical puncture accuracy, 2) minimized the radiation exposure during the operation, 3) shortened the surgical procedure time, and 4) decreased the probability of puncture-related complications.
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Protocol
The present study was approved by the ethics committee of Beijing Friendship Hospital Capital Medical University.
1. Diagnosis of the osteoporotic vertebral compression fracture (OVCF) by X-ray fluoroscopy, magnetic resonance image (MRI), bone scintigraphy, and symptoms
- Identify patients who have OVCF by older patients with back pain, tenderness in the spinous process, paraspinal muscles at back, etc.
- Use posterioanterior X-ray fluoroscopy to check if patient has vertebral compression fracture.
- Use an MRI to diagnosis whether a patient has a newly onset vertebral compression fracture, and determine the target compressed vertebrae. For patients who cannot undergo the MRI, use bone scintigraphy.
- Order PVP treatment for the patient who has an acute vertebral compression fracture and record the Visual Analogue Scale (VAS) score and Oawestry Disability Index (ODI)8.
NOTE: There are a few criteria for inclusion: 1) vertebra fractured patient whether having history of a low-energy trauma or not; 2) no history or evidence of metabolic bone disease or cancer; 3) VAS score ≥ 7; 4) diagnosis as vertebral fracture by X-ray, MRI or bone scintigraphy.
2. Preoperative localization of target vertebra
- Before the operation, conduct prone computer tomography on the patient with three radiopaque markers placed in the midline of patient's back skin at the compressed vertebral level. While pressing the most painful part, confirm the target area by x-ray fluoroscopy and a physical examination on the patient's back.
- Before the prone computer tomography scan, put a gradienter on the patient's back just inferior to the fixed markers. Record the patient's body position and then remove it. Have the patient stay in the same position during surgery.
- Save the CT images (1 mm scanning layer thickness, 1 mm layer spacing, and either 90 slices (conventional scanning) or 400 slices (thin slice scanning) in a DICOM format. Put a cotton pad on the patient's back to ensure that the markers remain until the operation.
3. Simulating the percutaneous vertebroplasty procedure in the computer software
- Export the CT images in DICOM format into medical imaging processing software (e.g., MIMICS) and select the target slices to reconstruct the compressed vertebra.
- Select Threshold Segmentation to adjust the threshold range for the target vertebra from 125-3071H and create a mask. Press Duplicate Mask to make two masks: Mask A and Mask B.
- Click Mask Edit to erase the target vertebra in Mask A. Then click Boolean Operations to form a new Mask C by using Mask B to minus Mask A. Press Calculate 3D from Mask to reconstruct the target vertebra.
- Simulate PVP via a bilateral transpedicular approach in the software. First, define the Medcad cylinder in the software as the puncture needle model. Define the cylinders as the same length and radius as the puncture needle (a length of 125 mm and a radius of 1.25 mm).
- Simulate the entry point, the entry angle (head inclination angle and abduction angle orientation), and the puncture needle depth for a real PVP with the 3-D views of the target vertebra.
- Adjust the puncture needles to its ideal position by using the Move and Rotate function. Keep needle trajectories consistent with these principles: 1) the puncture needles can extrapolate through the pedicle, preferably in its superior half; 2) the ideal location of the tips is at the point within the anterior one third of the vertebral body on the lateral view.
4. Three-dimensional printing guide template
- Save all of the 3D template data and send it in the MCS format to a three-dimensional printing company.
- Convert MCS format data into a STL format and design the template using software. Reconstruct the base, which must cling to patient's back skin, reconstruct the trajectory canal according to all of the parameters, including skin entry points, entry angles and the depth of the two needles' trajectory, print two same templates out for the operation.
NOTE: The guide template is made from polylactic acid, which can be sterilized and by low temperature steam disinfection.
5. Applying the three-dimensional printing guide template to assist the real PVP operation
- Make the patient lie prone on the operation table as for the CT scanning in accordance with the gradienter record. Measure the distance of the three radiopaque markers and draw the outline of the three markers to match the template with the target location.
- Match a skin template along with the skin outline. Insert and press two swabs through the needle's trajectories on the template to mark the insertion points on the skin. Then remove the template and draw the points as point A and B.
- Remove the template and disinfect the skin. Drape the area and put the tips of two puncture needles at the insertion points (point A and B). Then, use the anteroposterior view of C-arm fluoroscopy to confirm whether the puncture points determined by template are feasible.
- Give the patient local anesthesia by injecting a 5 mL mixture of 1% lidocaine and 1% ropavicaine at each puncture point. Fix another sterilized template on the patient's back by sterilized film.
- Tap the two needles into the target vertebra slightly via insertions through the guiding cylinders of the template. Verify with the C-arm fluoroscope that the trajectories are suitable for insertion. Make sure that the punctuation is within the pedicles and then tap the needles to advance further until the end of the trajectory.
- When the whole needles are completely inserted into the guiding cylinders, verify with the C-arm fluoroscope that the needle tips have reached their ideal location.
- Inject bone cement into the vertebral body through the needles. Inject 2 mL of bone cement via each trajectory for a total of 4 mL of bone cement to the vertebra.
- Finally, use fluoroscopy to check the distribution of the bone cement within the vertebral body by anteroposterior and lateral views. Stitch the insertions.
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Representative Results
Acquisition of CT images and digital modeling were performed in the hospital, while 3-D printing was performed in a 3-D printing company. Thirty minutes were needed to reconstruct the 3-D model from the CT images for the 3-D printing, and the 3-D printing company needed about 6 hours to print 2 guide templates out and send to the hospital.
The pre-operation images of the target vertebra of the patient were shown in Figure 1 and Figure 2: X-ray (A1: Posterioanterior view; A2: Lateral view); magnetic resonance image (A3: TIWI view; A4: T2WI view; A5: FS view). Figure 3 illustrates the acquisition of CT images, marks the target vertebrae, and records the patient's body position. From the coronal plane (Figure 4A), the transverse plane (Figure 4B) and the sagittal plane (Figure 4C), the CT vertebra image was reconstructed into a 3-D model (Figure 4D). The simulation of the PVP operation procedure in the image processing software is shown in Figure 5. Figure 6 presents the length of guiding cylinders of the template, and Figure 7 shows the procedures to fabricate the guide template. Figure 8 shows the formation of the base (Figure 8A), the formation of the guiding cylinder (Figure 8B), the production process (Figure 8C), and the final template (Figure 8D). Figure 9 shows typical operation steps.
Figure 1: X-ray of the OVCF patient. Shows the pre-operation X-ray images of the target vertebra of the patient. (A1: Posterioanterior view; A2: Lateral view). Please click here to view a larger version of this figure.
Figure 2: MRI of the OVCF patient. Shows the pre-operation MRI images of the target vertebra of the patient. (A3: TIWI view; A4: T2WI view; A5: FS view). Please click here to view a larger version of this figure.
Figure 3: Preoperative localization of target vertebra. Illustrates the acquisition of CT images, marking of the target vertebrae, and recording of the patient's body position. Please click here to view a larger version of this figure.
Figure 4: Reconstruction of vertebra in MIMICS. Presents the reconstructed vertebra model from the CT vertebra image from (A) the coronal plane, (B) the transverse plane, (C) the sagittal plane and (D) the 3-D model. Please click here to view a larger version of this figure.
Figure 5: Simulation of PVP operation procedure in the MIMICS. Shows the simulation of PVP operation procedure in the MIMICS. Please click here to view a larger version of this figure.
Figure 6: Date of guiding cylinders of the template. Presents the length of guiding cylinders of the template. Please click here to view a larger version of this figure.
Figure 7: The procedures of fabricate the guide template. Illustrates the steps to fabricate the template, including reconstructing the base and the trajectory canal. Please click here to view a larger version of this figure.
Figure 8: The model of guiding template. Shows (A) the formation of the base, (B) the formation of the guiding cylinder, (C) the producing process and (D) the real template entity. Please click here to view a larger version of this figure.
Figure 9: Typical operation steps. (A) Use the gradienter to ensure that the patient is in the same position when the CT was performed; (B) Match one template with skin to determine the puncture points; (C) Final puncture points; (D) Use the puncture needles to double check the puncture points; (E) Fix the other sterilized template and insert the needles; (F) Tap the needles to the end of the trajectories; (G) Inject bone cement bilaterally via the needles; (H) Final fluoroscope of the distribution of bone cement within the vertebral body. Please click here to view a larger version of this figure.
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Discussion
Percutaneous vertebroplasty (PVP) is considered one of the best methods to treat osteoporotic vertebral compression fracture9 due to some distinct advantages: it is minimally invasive; there is less bleeding, and recovery is rapid. Traditional PVP is primarily guided by a C-arm fluoroscope that requires repeated fluoroscopy to determine safe and ideal puncture points, puncture angles and orientations, which increases the intraoperative radiation dosage and the operation time10. Moreover, the success rate of the operation relies mainly on the experience of the surgeons. However, there are still 1.2%-15.7% error rates and 0-7.42% reoperation rates, even for operations assisted by an image-guided navigation system11.
A 3D guide template has some advantages for assisting in thoracic and cervical pedicle screw insertion operations12,13,14. Our team combines a 3-D printing guide template with PVP. The results of our randomized, nonblinded, controlled clinical study show that the template provides many advantages before and during the operations: increased puncture precision; minimized surgical time and radiation exposure; and decreased puncture-related complications. For medical residents with less opportunity to perform the operation on patients, the template could shorten the learning curve of the operation and help them find the puncture points easier.
Moreover, our clinical task research focuses on applying a 3-D guide template into one segment OVCF patients. In the future, we will apply the guide template into complicated OVCF patients with severe osteoporosis, severe kyphosis, scoliosis or multi-segment fractured vertebra. These complicated OVCF operations require multiple fluoroscope scans and have long operational times, even for experienced surgeons. Applying the 3-D guide template for these cases offers a more precise and safer puncture approach, reduces operation time, and reduces radiation exposure.
However, there are some limitations of the three-dimensional printing guide template assisted percutaneous vertebroplasty. Time is required to grasp the use of the medical imaging software. During the template design, any single mistake made by surgeons unfamiliar with the software may lead to an unsuccessful surgery. Hence, this method requires that at least one surgeon in the team is familiar with the software usage as well as the operation procedures. Preoperative design of the template and template printing increase patient costs and the surgeon's workload. Sometimes, the template becomes slightly deformed after the sterilization, which impacts the perfect attachment of the template to the patient's back skin and the puncture accuracy. Therefore, our team is seeking alternative materials for template fabrication that would not deform after sterilization.
Collectively, 3D printing guide template assisted percutaneous vertebroplasty could help surgeons comprehensively visualize the fractured vertebra and develop an individualized surgical plan for the patient. It contributes to puncture accuracy during the procedure and decreases puncture-related complications. It minimizes the surgical time and radiation exposure while shortening the PVP learning process for young surgeons.
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Disclosures
The authors have no conflict of interest regarding any drugs, materials, or devices described in this study.
Acknowledgments
The study was funded by the Beijing Municipal Science & Technology Commission (No.Z181100001718078), China.
Materials
| Name | Company | Catalog Number | Comments |
| X-ray machine | Company Philips | machine | |
| Magnetic resonance image machine | Company GE | machine | |
| computer tomography | Company GE | machine | |
| HORI 3D printing machine | Company of Beijing Huitianwei Technology co. ltd. | machine | |
| Geomagic Design X | 3D Systems Company | software | |
| Materialise Interactive Medical Image Control System | Materialise Company | software | |
| VertePort needle | Stryker Company | operation appliance | |
| Spineplex | Stryker Company | operation appliance | |
| Percutaneous Cement Delivery System | Stryker Company | operation appliance | |
| Spirit Level Plus | IOS App store | gradientor |
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