Three-Dimensional Printing Guide Template Assisted Percutaneous Vertebroplasty (PVP)

Podsumowanie

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.

Streszczenie

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.

Wprowadzenie

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.

Protokół

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

1. Identify patients who have OVCF by older patients with back pain, tenderness in the spinous process, paraspinal muscles at back, etc.
2. Use posterioanterior X-ray fluoroscopy to check if patient has vertebral compression fracture.
3. 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.
4. 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

1. 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.
2. 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.
3. 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

1. 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.
2. 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.
3. 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.
4. 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).
5. 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.
6. 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

1. Save all of the 3D template data and send it in the MCS format to a three-dimensional printing company.
2. 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

1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.
7. 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.
8. Finally, use fluoroscopy to check the distribution of the bone cement within the vertebral body by anteroposterior and lateral views. Stitch the insertions.

Wyniki

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

Dyskusje

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

Materiały

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