Nine-Grid Area Division Method: A New Ideal Bone Puncture Region for Percutaneous Vertebroplasty in Lumbar Spine

Summary

Herein, we present a "Nine-grid Area Division Method" for percutaneous vertebroplasty. A patient with an L1 vertebral compression fracture was selected as a case study.

Abstract

Percutaneous vertebroplasty (PVP) is widely recognized as an efficacious intervention for alleviating low back pain resulting from osteoporotic vertebral compression fractures. The ideal bone puncture point is conventionally situated at the projection "left 10 points, right 2 points" of the pedicle in the lumbar spine. Determining the optimal bone puncture point represents a critical and complex challenge. The accuracy of percutaneous vertebroplasty (PVP) is primarily influenced by the proficiency of the operating surgeons and the utilization of multiple fluoroscopes during the conventional procedure. Incidences of puncture-related complications have been documented globally. In an effort to enhance the precision of the surgical technique and reduce the occurrence of puncture-related complications, our team applied the "Nine-grid Area Division Method" for PVP in the lumbar spine to modify the traditional procedure. There is potential to decrease the number of puncture times, the radiation exposure dosage, and the duration of surgical procedures.

This protocol introduces the definition of the "Nine-grid Area Division Method" and describes the process of modeling target vertebrae DICOM imaging data within medical imaging processing software, simulating operations within a 3-D model, refining the 3-D model using reverse engineering production software, reconstructing the vertebral engineering model within 3-D modeling design software, and utilizing surgical data to determine safe entry regions for pedicle projection. By employing this methodology, surgeons can effectively identify appropriate puncture points with precision and ease, thereby reducing the intricacies associated with puncturing and enhancing the overall accuracy of surgical procedures.

Introduction

Osteoporotic vertebral compression fracture (OVCF) is the most prevalent type of fracture among osteoporotic fractures and poses a significant clinical concern in contemporary healthcare¹. According to current guidelines, percutaneous vertebroplasty is recognized as one of the most efficacious minimally invasive treatment modalities for OVCF². The predominant method for performing percutaneous vertebroplasty (PVP) involves the pedicle puncture approach, which encompasses three key parameters: the identification of the bone puncture entry point, puncture angle, and puncture depth. Of these parameters, the selection of the bone puncture entry point is considered the most crucial.

Currently, C-arm X-ray machines are widely employed in the domestic and international practice of traditional PVP surgery to facilitate the adjustment of the surgical path of the puncture needle. The crucial aspect lies in identifying the "ideal bone puncture point," which is conventionally situated at the projection "left 10 points, right 2 points" of the pedicle in the lumbar spine (Figure 1A)³. Despite their experience, even seasoned surgeons may make mistakes when determining appropriate puncture points based solely on personal experience. This can lead to puncture-related complications such as cement leakage into surrounding tissues, nerve root injury, and intra-spinal hematoma^4,5,6. Additionally, nearly half of patients experience local complications from traditional PVP, with 95% of these complications attributed to cement leakage into surrounding tissue or embolization of paravertebral veins⁷. Our preliminary research found that the actual PVP bone puncture points in the lumbar spine are not always located at the ideal pedicle projection "left 10 points and right 2 points"⁸. Some actual puncture points can also achieve satisfactory puncture results near the "ideal bone puncture point," which does not affect surgical safety and accuracy.

Based on the above assumptions, we propose, for the first time, the concept of the "ideal bone puncture region" for PVP in the lumbar spine and divide the projection of the pedicle into a "Nine-grid Area". The concept of the ideal bone puncture region pertains to specific anatomical regions where the puncture entry point can successfully and securely reach the puncture ideal endpoint through the pedicle.The term "Nine-grid Area Division Method" refers to a technique in the X-ray anteroposterior image whereby the longest and shortest diameters of the pedicle projection are divided into three equal parts, resulting in the division of the area into nine regions (Figure 1B). These regions are sequentially numbered from 1 to 9, progressing from the outermost to the innermost and from top to bottom. Using the X-ray projection of the lumbar pedicle as an anatomical marker, we establish the "ideal bone puncture region" for PVP through the "Nine-grid Area Division Method" instead of being confined to a single point. We use computer simulation to explore a safe puncture path during the puncture process.

Hence, we suggest the implementation of the "Nine-grid Area Division Method" as a potential method for enhancing the convenience, efficiency, and safety of auxiliary puncture techniques in PVP surgery, with the aim of enhancing procedural accuracy and minimizing puncture-related complications. It is important to note that this study presents a theoretical approach that requires validation through extensive research to ascertain its efficacy and safety.

Protocol

The present study was approved by the Ethics Committee of Beijing Friendship Hospital Capital Medical University. This method will be introduced via a retrospective case study, utilizing only the preoperative prone-position computed tomography (CT) imaging data of the patient. The "Nine-grid Area Division Method" in assisted percutaneous vertebroplasty (PVP) offers a simpler and more effective approach compared to traditional methods, resulting in reduced surgical and radiation exposure times. This technique may benefit young residents by facilitating easier identification of puncture points and potentially shortening the learning curve for PVP procedures, warranting further investigation. The individual described here is a female of 68 years of age.

1. Diagnosing osteoporotic vertebral compression fracture (OVCF) using X-ray fluoroscopy, magnetic resonance image (MRI), bone scintigraphy, and symptoms

1. Identify the patient who has OVCF among older patients with symptoms such as back pain, tenderness in the spinous process, and paraspinal muscles at the back. Utilize posteroanterior X-ray fluoroscopy to assess for the presence of a vertebral compression fracture at the L1 level (Figure 2A). Employ MRI imaging to confirm the diagnosis of a newly occurring lumbar vertebral compression fracture and identify the specific vertebra affected, which is determined to be L1 (Figure 2B).

2. The preoperative acquisition of CT imaging of the patient in a prone position

1. Place the patient in a prone position to perform prone CT on the patient. Confirm the target area by x-ray fluoroscopy and a physical examination of the patient's back while pressing the most painful part.
2. Make the patient lie in a prone position on the operation table, place a gradienter on the patient's back before the prone CT scan, record the patient's body position, and then remove the gradienter (Figure 3).
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 DICOM format.

3. Establish the 3-D model and simulate the operation in medical imaging processing software

1. Export the CT images in DICOM format into medical imaging processing software by clicking New Project. Select the desired slices for reconstructing the compressed vertebra.
2. Utilize the Threshold Segmentation tool to adjust the threshold range for the target vertebra, specifically within the range of 125-3071 H to create a mask. Employ the Duplicate Mask function to generate two separate masks, Mask A and Mask B.
3. Utilize the Mask Edit feature to erase the target vertebra from Mask A. Subsequently, utilize the Boolean Operations tool to subtract Mask A from Mask B, resulting in the formation of a new mask, Mask C. Finally, activate the Calculate 3-D function to reconstruct the target vertebra using the Mask C; name this 3-D model L1 (Figure 4A).
4. Right-click on New in the Objects interface, choose Draw, and subsequently select Cylinder. Ensure that the cylinder has the same dimensions as the puncture needle, with a length of 12.5 mm and a radius of 1.25 mm.
5. Adjust the positioning of the cylinder using the Move and Rotate function to achieve the ideal position (Figure 4B). Throughout the simulation, take care to maintain needle trajectories consistent with established principles: the puncture needle must be able to traverse the pedicle, preferably in its superior half, and the optimal positioning of the tips is within the anterior one-third of the vertebral body on the lateral view.
6. Right-click on L1 in the Objects interface, choose Export STL, and subsequently export the file in STL format.

4. Polish the 3-D model in 3-D reverse engineering production software

1. Import the exported vertebral body solid file into the 3-D reverse engineering production software by clicking Import. Consequently, employ the Mesh Doctor feature to eliminate distortions and spikes from the model.
2. As the Grid Doctor function may mistakenly identify normal anatomical structures as distortions or spikes, take care to thoroughly examine the rough model to identify any internal voids, and follow step 4.1 to fill them appropriately (Figure 5A).
3. Employ the Precise Surface function to transform the solid model into a triangular mesh surface, opting for the Organic Geometry Material (Figure 5B). Await the completion of the automated surface construction process and subsequently export the file in STP format.

5. Reconstruct the vertebral engineering model and confirm the safe entry regions of pedicle projection in 3-D modeling design software

1. Import the STP format of the precise surface document into 3-D modeling design software to reconstruct the vertebral engineering model by clicking Open. Employ the Section View feature to examine the pedicle's morphology in horizontal, sagittal, and coronal orientations, providing an initial observation of the pedicle's morphology and structure (Figure 6A).
2. In the Section View panel, adjust the angle of the section for optimal visualization. By utilizing Transparency Section Bodies, observe the narrowest point of the pedicles (Figure 6B) and record the angle parameters at Section 1 in the left panel.
3. To adjust the angle of the vertebral model, click on the Insert-Features-Move/Copy function and select the Translate/Rotate button located at the bottom of the left panel. Revisit the Section View panel and adjust the view angle parameter in Section 1 to 0.
4. Fine-tune the displacement parameters in the Section 1 panel to attain a satisfactory pedicle section view. Reorient for an improved perspective to observe the pedicle section. Document the confirmed displacement parameters in the panel (Figure 7).
5. Utilize the aforementioned Move/Copy function to manipulate the position of the vertebral model. Specify the displacement parameter in the left panel. Employ the Corner Rectangle tool to encompass the entirety of the vertebral body.
6. To begin, navigate to the Features-Reference Geometry-Plane option and designate the section view as the First Reference. Modify the offset distance parameter accordingly to relocate the newly created plane to the anterior third of the vertebral body.
7. Proceed to generate a Sketch on the aforementioned plane and draw a Point at the midpoint of the vertebral body, signifying the termination point of the puncture.
8. Use the Extruded Cut function to perform the cutting of the model. Designate the rectangular sketch generated as the Selected Contours.
9. Make adjustments to both the direction and depth to divide the vertebral body model into two halves, namely the vertebral body half and the lamina half (Figure 8A). Save the engineering files in SLDPRT format, specifically as part of the process.
10. Open the file containing the vertebral body part, followed by the creation of a sketch based on the section plane. Use the Convert Entities function to convert the left pedicle projection into a curve sketch.
11. Repeat the above procedure for the right pedicle projection, resulting in the acquisition of another curve sketch. Employ the Filled Surface function to transform the curve sketches into surfaces, with the left and right pedicle projection curve sketches serving as the boundary (Figure 8B).
12. Display the resulting surface after the vertebra has been concealed. Select the Lofted Boss/Base function on the Features panel.
13. The superior positioning of the left pedicle surface, with the designation of the puncture endpoint as Profiles, will yield a conical structure delineating the paths for pedicle puncture. Use the left side as a reference for illustrative purposes, with the same process to be replicated on the right side.
14. Use the Scale function to magnify the bilateral conical structure, with the centroid serving as the scaling center point and a scale factor of 2. Employ the Move/Copy Body function to individually relocate the conical structures.
15. Within the Mate Setting panel interface, select the apex of the structure and the puncture end point, with the matching mode set as Coincident. Eliminate the vertebral body subsequently using the Delete/Keep Body function (Figure 9A).
16. The biconical structure is a compilation of bilateral pedicle puncture paths, saved in SLDPRT format. Employ the Insert Part function to reassemble the lamina part and the vertebral body part using the pedicle puncture set. Simply press the OK button to automatically align the insert position of the part with the origin (Figure 9B).
17. Employ the Combine Body function for executing Boolean operations on various components. Through the process of subtracting the puncture set from one half of the laminae while retaining all laminae components, the subsequent analysis indicates that the ideal bone puncture region includes regions 1, 4, and 7 on the left side (Figure 9C).

Results

CT imaging and digital modeling were performed in the hospital. It took 30 min to build the 3-D model from the CT images, ~10 min to polish the 3-D model in 3-D reverse engineering production software, and 15 min to reconstruct the vertebral engineering model and confirm the safe entry regions of pedicle projection in 3-D modeling design software. The ideal bone puncture region includes regions 1, 4, and 7 on the left side in this case. The notion of the ideal bone puncture region refers...

Discussion

Percutaneous vertebroplasty (PVP) has demonstrated favorable clinical efficacy in managing painful osteoporotic vertebral compression fractures (OVCF)⁹. The utilization of precise percutaneous pedicle puncture technology by surgeons plays a crucial role in determining the optimal insertion point, direction, and depth of the puncture needle, thereby significantly reducing the occurrence of complications¹⁰. Currently, C-arm X-ray machines are widely employed in the domestic a...

Materials

Name	Company	Catalog Number	Comments
Computer tomography	Company GE		machine
Geomagic Wrap (3-D reverse engineering production software)	Oqton software		software
Magnetic resonance image machine	Company GE		machine
Materialise Interactive Medical Image Control System (medical imaging processing software)	Materialise Company		software
Solidworks (3-D modeling design software)	Dassault Systèmes - SolidWorks Corporation		software
Spirit Level Plus	IOS App store		gradientor
X-ray machine	Company Philips		machine