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Fixation of the thoracolumbar spine with augmented reality-supported rod bending in multilevel pedicle screw instrumentation: First results of a prospective pilot study

This prospective pilot study demonstrates that augmented reality-assisted rod contouring using the ADVISE system is a feasible and safe technique for multilevel thoracolumbar pedicle screw instrumentation, resulting in significant clinical improvements and eliminating the need for forceful rod reduction maneuvers without observed implant-related complications.

Original authors: Bernardo Reyes Medina, Christoph Sippl, Fatemeh Khafaji, Shafie Ariai, Saffwan Saffour, Stefan Linsler

Published 2026-06-30

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Bernardo Reyes Medina, Christoph Sippl, Fatemeh Khafaji, Shafie Ariai, Saffwan Saffour, Stefan Linsler

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Big Picture: Fixing a Wobbly Shelf

Imagine your spine is like a tall, heavy bookshelf. When the shelves (vertebrae) get weak or wobbly due to age or wear and tear, doctors need to bolt them together to make them stable again. They do this by driving metal screws into the "wood" of the spine and connecting them with a long metal rod, kind of like running a metal bar through the holes of the bookshelf to lock it in place.

For a long time, the hardest part of this job has been bending that metal rod. The rod needs to fit perfectly into every single screw. If the rod is even slightly too straight or too curved compared to where the screws are, the doctor has to use a lot of brute force to jam the rod into place.

The Problem: Think of trying to force a straight stick into a curved hole. If you push too hard, you might crack the wood around the hole or loosen the screw itself. In spine surgery, this "forced fit" creates stress that can cause the screws to loosen or pull out later, leading to pain and more surgeries.

The New Tool: A "Magic" Blueprint

This study tested a new technology called Augmented Reality (AR) to help doctors bend the rod perfectly the first time.

Imagine you are trying to build a custom frame for a picture. Instead of guessing the shape, you hold up a tablet that sees the picture frame and draws a perfect, glowing outline of exactly how the frame needs to be cut. That is what the ADVISE system did for the surgeons.

The Scan: After the screws were already in the patients' backs, the surgeon used a tablet (covered in a sterile plastic bag) to scan the area.
The Blueprint: The tablet's camera saw the screws and, using 3D technology, calculated the exact curve needed for the metal rod to slide in without any force.
The Fit: The tablet showed the surgeon a digital "ghost" of the rod on the screen. The surgeon then bent the real metal rod to match that digital shape.

What They Did in the Study

The researchers at Bayreuth Medical Center in Germany tested this on 20 patients who needed surgery on multiple levels of their lower back (thoracolumbar spine). These were mostly older adults (average age 72) with degenerative spine issues.

The Goal: To see if this "magic blueprint" method was safe, easy to use, and if it helped the patients feel better.
The Process: They used the AR system to guide the rod bending for every single patient.

The Results: A Perfect Fit

The study found that the new method worked very well:

No Struggle: In every single case, the rod slid into the screws smoothly. The surgeons didn't have to use any "forceful reduction maneuvers" (no jamming or prying). It was like sliding a key into a lock that fits perfectly, rather than forcing a key that's the wrong shape.
No Breakages: During the surgery and the three months after, zero screws loosened, zero rods broke, and zero screws pulled out. This is a big deal because, in traditional surgery, these complications happen fairly often, especially in older patients with weaker bones.
Less Pain: The patients' pain scores dropped significantly. Before surgery, they rated their pain as an 8 out of 10. Three months later, it was down to a 4 out of 10. Their ability to move and function (measured by a disability index) also improved greatly.
Speed: The technology didn't slow things down. It only took about 3 to 5 minutes to scan the screws and generate the rod template.

The Conclusion

The study concludes that using this Augmented Reality system is safe and feasible. It acts like a GPS for the metal rod, ensuring it fits the screws perfectly without needing to force it.

What the study did not claim:

They did not say this is a cure for all spine problems.
They did not claim it works better than traditional methods yet (because they didn't compare it directly to a group of patients who didn't use the robot).
They did not know if the screws would stay secure for 5 or 10 years, because they only followed the patients for three months.

In short: This pilot study showed that giving surgeons a "digital blueprint" to bend the metal rods helped them avoid forcing the hardware, resulting in a smooth surgery with no immediate screw failures and happy patients. It's a promising new tool that needs more testing over a longer time to see if it keeps the spine stable for years to come.

Technical Summary: AR-Supported Rod Bending in Thoracolumbar Spine Fixation

Problem Statement
Pedicle screw fixation is the gold standard for thoracolumbar spinal stabilization; however, it is frequently associated with implant-related complications, particularly screw loosening and pullout. These failures are often attributed to mechanical stress generated at the bone–implant interface during the rod insertion phase. When there is a mismatch between the trajectory of the pedicle screws and the contour of the connecting rod, surgeons must employ forceful reduction maneuvers to seat the rod. This process can induce significant tension, leading to screw loosening (reported rates up to 27% in patients with good bone quality and over 50% in osteoporotic patients), rod fractures, and subsequent revision surgery. Traditional rod contouring relies on surgeon experience and visual estimation, which often necessitates repeated bending adjustments and excessive force. While computer-assisted systems have shown promise in reducing pullout forces, there is a lack of clinical evidence regarding the use of Augmented Reality (AR) for rod contouring in multilevel spine fixation.

Methodology
This study was a prospective, single-centre pilot trial conducted at Bayreuth Medical Center between August 2024 and February 2026. It enrolled 20 consecutive patients (mean age 71.6 years) undergoing multilevel posterior thoracolumbar instrumentation for degenerative spinal pathologies (involving at least three contiguous segments).

The core intervention involved the use of the ADVISE system (Neo Medical, Switzerland), an AR-based rod contouring software. The technical workflow proceeded as follows:

Screw Insertion: Pedicle screws with removable guides were inserted into the vertebrae.
3D Scanning: Using an iPad enclosed in a sterile cover, the surgeon scanned the surgical field. The software utilized LiDAR and computer vision to detect the position of the removable guides attached to the screw heads.
Virtual Modeling: The software superimposed virtual guide models onto the physical guides to confirm alignment. It then calculated the precise 3D positions of the screw heads and the distances between them in both sagittal and coronal planes.
Template Generation: Based on these measurements, the system generated a patient-specific rod template displayed at a 1:1 scale on the iPad. This template dictated the exact length and curvature required for the rod.
Rod Contouring and Insertion: Surgeons cut and bent the rods according to the digital template. The system provided visual feedback (via markers on the set-screw driver) to confirm the rod was seated in a stress-free position without the need for reduction maneuvers.

Key Contributions

First Clinical Evidence: This study provides the first prospective clinical data on the feasibility and safety of AR-assisted rod contouring specifically for multilevel thoracolumbar instrumentation.
Workflow Integration: It demonstrates a streamlined workflow where the AR scanning and template generation phase adds only 3 to 5 minutes to the procedure without disrupting sterility or surgical flow.
Stress-Free Fixation: The study validates a method for achieving "controlled fixation" where the rod aligns perfectly with the screw heads, theoretically eliminating the need for forceful reduction maneuvers that cause mechanical overload.

Results

Feasibility and Safety: All 20 procedures were successfully completed using the AR-assisted workflow. There were no intraoperative screw pullouts, implant-related technical failures, or complications attributable to the AR system.
Implant Integrity: A total of 206 pedicle screws and 40 rods were implanted. At the three-month follow-up, no cases of screw loosening, rod fracture, implant migration, or construct disassembly were observed. Radiographic evaluation (CT and fluoroscopy) confirmed accurate screw placement (all Grade A or B per Gertzbein–Robbins classification) and stable constructs.
Clinical Outcomes: Significant improvements were recorded in pain and functional disability:
- VAS (Visual Analogue Scale): Improved from a mean of 8.0 preoperatively to 4.0 at three months ( $p < 0.001$ ).
- ODI (Oswestry Disability Index): Improved from 69.2 preoperatively to 45.6 at three months ( $p < 0.001$ ).
- MacNab Criteria: At three months, 60% of patients achieved "good" or "excellent" outcomes.
Operative Metrics: The mean operative time was approximately 350 minutes, with blood loss averaging 1170 ml. The specific time to generate the rod template was negligible (mean 3.5 minutes).

Significance and Claims
The authors claim that the ADVISE AR system is a feasible and safe tool for multilevel thoracolumbar instrumentation that facilitates improved rod–screw alignment. By enabling the creation of patient-specific rods that match the exact screw trajectory, the technology allows for fixation without external reduction forces. The study posits that this "controlled fixation" approach may reduce the mechanical stress that typically leads to screw loosening and pullout.

However, the authors maintain a modest stance regarding the long-term implications. They explicitly state that while the short-term results (3 months) show no complications and significant clinical improvement, the study was not powered to detect rare complications or long-term differences compared to conventional methods. The authors conclude that larger comparative studies with extended follow-up are necessary to definitively determine the impact of this technology on implant survival, pseudarthrosis, and adjacent segment degeneration. The current significance lies in establishing the technical viability and safety of integrating AR into the rod contouring workflow.