Three-Dimensional Reconstruction–Guided Development of a Percutaneous Endoscopic Lumbar Disc Positioning Device in a Porcine Spine Model

Summary

The percutaneous endoscopic intervertebral disc positioning device developed in this study can assist in the positioning of intervertebral discs. This device reduces radiation exposure and supports technical training for young spinal surgeons.

Abstract

Lumbar disc herniation (LDH) is commonly caused by annular disruption resulting from trauma or poor posture, leading to extrusion of nucleus pulposus material and compression of lumbar nerve roots. This condition often presents with radicular pain and sensory disturbances radiating from the lower back to the lower extremities. Although most cases can be managed conservatively, severe or refractory symptoms may require surgical intervention, including conventional discectomy, minimally invasive microscopic discectomy, and endoscopic discectomy. Percutaneous endoscopic lumbar discectomy (PELD) can be performed under local anesthesia; however, the procedure relies heavily on the surgeon's experience and is associated with technical challenges, including positioning difficulty, repeated fluoroscopic confirmation, and increased radiation exposure. The objective of this study was to develop and evaluate a novel percutaneous endoscopic lumbar disc positioning device designed to improve the precision and efficiency of disc positioning during PELD. This study developed a unique percutaneous endoscopic lumbar disc positioning device. The device was realized through the reconstruction and repair of 3D models of the porcine spine and lumbar spine, fabrication of a convex base plate, design of spinal spinous process and disc positioning guiding devices, computer-aided design of a percutaneous endoscopic lumbar disc minimally invasive surgical navigation module, and accuracy testing. Experimental results showed that the device could accurately locate positions on porcine spines and may reduce fluoroscopic dependence in experimental settings. The positioning device provided high precision, supporting minimally invasive surgery by reducing incision size, avoiding damage to surrounding critical blood vessels and nerve tissues, and offering multi-directional surgical instrument guiding paths, facilitating the surgical process. The percutaneous endoscopic lumbar disc positioning device described in this study provides a structured, reproducible approach to intervertebral disc positioning during PELD. This method has the potential to improve procedural efficiency, limit radiation exposure, and support surgical training, particularly for early-career spine surgeons.

Introduction

Lumbar disc herniation (LDH) involves the extrusion of the nucleus pulposus through an annular defect into the spinal canal or neural foramen, resulting in lumbar nerve root compression. Clinical symptoms such as sharp pain, leg cramps, and numbness are presented, and even muscle weakness, atrophy, urinary and fecal incontinence can occur as permanent sequelae¹. Although most patients respond to conservative treatment, surgical intervention is required for those with refractory symptoms or progressive neurological impairment.

Several surgical techniques have been developed for the management of severe LDH, including conventional posterior lumbar discectomy¹, minimally invasive microscopic discectomy^2,3, minimally invasive endoscopic discectomy^4,5, and percutaneous endoscopic lumbar discectomy (PELD)^6,7. Each technique has its pros and cons regarding the anaesthesia method, soft tissue intervention, positioning and navigation technique, and fluoroscopy requirement. PELD can be conducted under local anesthesia and has gained popularity due to its minimally invasive procedure. During PELD, real-time C-arm imaging is used to localize the insertion of a K-wire and working cannula through the intervertebral foramen to access the herniated disc fragment, which is then removed using endoscopic instruments. This technique has also been extended to the treatment of lumbar foraminal stenosis and selected cases of LDH^8,9. The advantages of this method include minimal soft tissue damage, less bleeding, faster recovery, and the feasibility of surgery under local anesthesia^10,11.

Despite these advantages, PELD presents technical challenges, particularly during the initial placement of the K-wire and working cannula. At present, these instruments are commonly inserted using a free-hand technique under continuous fluoroscopic guidance. This approach exposes surgeons to substantial radiation and requires a steep learning curve to accurately target the pathological disc fragment^11,12,13,14. In less experienced surgeons, inaccurate cannula placement may result in incomplete decompression and suboptimal clinical outcomes. Previous studies have reported higher recurrence and reoperation rates following PELD compared with traditional posterior discectomy^14,15,16. Furthermore, improper advancement of the K-wire or working cannula can lead to complications such as nerve root injury, vascular damage, or unintended penetration into the abdominal cavity^17,18.

To address the limitations of the conventional free-hand technique, we developed a unique device designed to assist spine surgeons in precisely targeting the pathological site while minimizing fluoroscopic exposure. This device is intended to shorten operative time, reduce radiation-related exposure risks, and lower the complications in PELD. This device facilitates the K-wire positioning stage of percutaneous endoscopic lumbar discectomy (PELD), particularly in precise path planning and entry point determination. Its application is especially advantageous in cases requiring precise complex anatomical configurations or reduced dependence on repeated C-arm imaging. We believe that this device can facilitate surgical performance by early-career spine surgeons, contribute to improved clinical outcomes, and significantly reduce the learning curve, while also serving as a valuable tool for surgical education and training.

Protocol

The porcine spine samples used in this article were procured from local commercial markets. Because these samples came from animals slaughtered for food purposes and without any live animal handling, they did not require review and approval by the Institutional Animal Care and Use Committee (IACUC).

This study developed a unique percutaneous endoscopic lumbar disc positioning device by reconstructing and refining three-dimensional (3D) models of the porcine spine specimens and lumbar spine simulation models. This device includes the guiding device, the navigation module, and the positioning device. The entire system was validated through positioning and alignment tests. The reagents and the equipment used are listed in the Table of Materials.

1. 3D model reconstruction and data preparation

1. CT scanning: Perform computed tomography (CT) scanning on porcine spine specimens and L1-sacrum lumbar spine simulated models.
   CAUTION: Scanning must be performed in a control room with a lead-glass observation window.
2. Set up the CT machine: 1 mm slice thickness, 300 mA tube current, 0.5 s rotation time, and 120 kV tube voltage.
   NOTE: Ensure consistent CT machine scan settings for each scan to maintain high-fidelity reconstruction.
3. Data export: Export the scanning results as DICOM image files for processing.
   NOTE: After exporting the 3D model to STL format, check the file for completeness before proceeding to the CAD design stage.
4. 3D reconstruction: Use MATLAB to convert the DICOM datasets into three-dimensional (3D) digital models and export STL files.
5. Model allocation: Designate the lumbar spine simulated model for device structural design and the porcine spine model for positioning accuracy verification.

2. Design and fabrication of the convex base plate

1. Reference mapping: Define the device positioning using the anterior superior iliac spine (ASIS) and the spinous process as anatomical reference points.
2. Base plate design: Design a convex base plate specifically configured to capture the 3D position of the ASIS while the patient is in the prone position.
   NOTE: The dovetail joint design tolerances are very small; the printed supports must be completely removed to minimize assembly errors.
3. Component segmentation: Divide the base plate design into four separate components connected by dovetail joints to facilitate assembly.
4. Mechanical testing: Fabricate the plate and perform mechanical testing to confirm it can support the prone body weight and resist physiological movement.

3. Design of the guiding device and navigation module

1. Spinous process capture: Design a dedicated structure to accurately capture the position of the spinous processes when oriented superiorly.
2. Data integration: Reconstruct a comprehensive 3D spinal model that incorporates the specific positional data of both the ASIS and the spinous processes.
3. Navigation module CAD: Use the integrated 3D model to design the intervertebral disc guiding device and the percutaneous navigation module using AutoCAD.
4. Reference point installation: Install predefined reference points onto the navigation module to ensure consistent intraoperative alignment.

4. Computer-Aided Manufacturing (CAM) and printing

1. Data preprocessing: Perform data cleaning on the spinal imaging files to remove redundant information and optimize computational efficiency.
2. Support structure design: Design customized support structures to accommodate the curved surface geometry of the spine model during the printing process.
3. FDM fabrication: Fabricate the physical spine model and navigation module using Acrylonitrile Butadiene Styrene (ABS) via Fused Deposition Modeling (Stratasys FDM). Printing parameters: nozzle 0.4 mm, layer height 0.1 mm, print speed 50 mm/s, bed temperature 100 °C, extrusion temperature 250 °C.
   CAUTION: Avoid contact with heated parts of the printer (nozzles and printing platform); wear heat-resistant gloves when handling newly printed parts; operate the printer in a well-ventilated area.
4. Process monitoring: Monitor the thermal extrusion process to ensure uniform material deposition; adjust parameters iteratively until the dimensions are accurate.

5. Accuracy testing and verification

1. Experimental setup: Mount the 3D-printed navigation module onto the porcine spine model.
2. K-wire insertion: Insert a 2.0 mm diameter K-wire through the navigation hole in the simulation.
   CAUTION: Wear protective gloves and goggles to avoid punctures; ensure the model is securely fixed during insertion.
3. Fluoroscopic confirmation: Capture C-arm fluoroscopic images from multiple angles to verify the K-wire’s position relative to the target intervertebral disc.
   CAUTION: Wear lead aprons, thyroid shields, and goggles; minimize fluoroscopy time and maintain a safe distance from the C-arm source.
4. Result analysis: Compare the physical K-wire placement against the 3D digital design to confirm the system's accuracy.
   NOTE: The complete workflow, including CT scanning, image processing, device design, and manufacturing, takes approximately 3–4 working days, depending on the complexity of the model. CT acquisition typically takes 30–45 min, followed by 2–4 h of DICOM processing and 3D reconstruction. Navigation module design takes approximately 4–6 h, and Fused Deposition Modeling (FDM) printing and post-processing take approximately 12–18 h.

Results

Using the reconstructed 3D model of the lumbar simulated bone model (Figure 1), with the positioning information of the anterior superior iliac spine (ASIS) and spinous process, we designed the "Percutaneous Endoscopic Lumbar Intervertebral Disc Positioning Device" (Figure 2). Initially, a scaled-down physical model was printed using FDM 3D printing technology (Figure 3) to verify structural feasibility. It was observed that the K-w...

Discussion

This study presents a protocol for the development and application of a Percutaneous Endoscopic Lumbar Intervertebral Disc Positioning Device designed to facilitate reliable positioning of the intended intervertebral disc space, as confirmed by fluoroscopic imaging, reduce operative time, and potentially improve patient outcomes in PELD. We integrated medical imaging, 3D reconstruction, and additive manufacturing to establish an external navigation framework based on reproducible anatomical reference lan...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
AutoCAD (CAD software)	Autodesk	https://www.autodesk.com/	Used for device and navigation module design
Fused deposition modeling (FDM) 3D printer	Stratasys	N/A	Used for fabrication of the device and models
Lumbar spine simulation model (L3–sacrum)	Sawbones	1340-20	Used for device design and procedural simulation
MATLAB (3D reconstruction software)	MathWorks	https://in.mathworks.com/	Used for 3D reconstruction from DICOM images