Methods to determine Pedicle Screw

Placement Accuracy in Spine Surgery

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Spine surgeons frequently utilize spinal fusion and pedicle screw fixation, which have been demonstrated to have significant advantages. Despite their proven benefits, spinal fusion and pedicle screw fixation do come with certain drawbacks, including pseudo arthritis, adjacent segmental degeneration, screw loosening, and incorrect screw placement.

Incorrect screw placement has the potential to cause a range of issues for patients, varying in severity from minor to major consequences. The consequences of incorrect screw placement may include neurological impairments, such as the onset of new radicular pain, sensory loss, or weakness, and can be as severe as paralysis.

While these risks are legitimate, they are typically minimal when surgeries are performed by qualified and experienced spine surgeons. Achieving precise screw placement is essential and a crucial factor in the success of the surgery.


Techniques for Pedicle Screw Placement

In certain situations, incorrect screw placement may lead to significant vascular damage, including aortic perforation. Surgeons usually obtain post-surgery images to evaluate and verify the precise positioning of pedicle screws. At present, there is no universally accepted or definitive method for evaluating the accuracy of pedicle screw placement.

Freehand Technique

The freehand technique is one of the oldest methods for placing pedicle screws. It relies heavily on the surgeon’s anatomical knowledge, tactile feedback, and experience. The process involves the surgeon manually guiding the screw into the pedicle without any real-time imaging assistance.

  • Advantages:

    • Flexibility in handling different anatomical variations.
    • Cost-effective as it does not require additional imaging equipment.
  • Disadvantages:

    • Highly dependent on the surgeon’s skill and experience.
    • Higher risk of inaccurate placement leading to potential complications.


Fluoroscopy Guidance

Fluoroscopy uses real-time X-ray imaging to guide the placement of pedicle screws. This technique provides the surgeon with continuous visual feedback, which helps in more accurate placement compared to the freehand method.

  • Advantages:

    • Improved accuracy over freehand technique.
    • Real-time imaging helps in adjusting screw trajectory during surgery.
  • Disadvantages:

    • Exposure to radiation for both the patient and the surgical team.
    • Requires additional equipment and training.


Navigation Systems

Navigation systems utilize preoperative or intraoperative imaging to create a 3D model of the patient’s spine. Surgeons use this model to guide the placement of pedicle screws with high precision.

  • Advantages:

    • High accuracy due to detailed 3D imaging.
    • Reduced risk of misplacement.
  • Disadvantages:

    • Expensive and requires specialized equipment.
    • Surgeons need specific training to use these systems effectively.


Robotic Assistance

Robotic systems are the latest advancement in spine surgery. They integrate navigation technology with robotic arms that assist surgeons in placing screws with extreme precision. These systems can follow pre-defined paths based on preoperative planning, minimizing human error.

  • Advantages:

    • Highest accuracy among all techniques.
    • Reduced complication rates.
  • Disadvantages:

    • Very high cost and significant setup time.
    • Requires extensive training for the surgical team.


The accuracy of screw placement is notably higher when a navigated technique is utilized in comparison to a free-hand technique. Screw placement accuracy varies depending on the grading system employed (2mm increment vs. in or out) and the region of the spine being operated on (thoracic vs. lumbar).

When a free-hand technique is used, the accuracy of screw placement is considerably greater with the 2mm grading system than with the “in” or “out” classification system. Employing a navigation technique and the 2mm increment grading system results in a markedly enhanced accuracy of screw placement, particularly in the thoracic region.

The greater precision of the 2mm classification system in detecting improperly positioned screws might help account for these findings. Additionally, since the placement of screws in the thoracic region is typically more difficult, it is not surprising that discrepancies were found between thoracic and lumbar screws depending on the grading system and surgical approach used.

Most of these grading systems are flawed because they do not take into account the direction of the breach. To illustrate, a breach categorized as grade B should be more worrisome if it is located medially and within the canal, compared to a similar graded screw that is laterally positioned and outside the facet joint or canal.

Moreover, there are cases where screws are deliberately positioned outside of the pedicle when there is a possibility of bone loss or compromise of the pedicle during surgery. To put it differently, a patient who presents with symptoms and an imaging-documented breach is more concerning in actual clinical practice than a larger breach that is visible on imaging but does not cause any symptoms in the patient.

The accuracy of screw placement is significantly higher when using a navigated technique as compared to the standard free-hand technique. Improved positioning of screws using imaging may result in enhanced patient outcomes, although it is uncertain if the improvement would have a significant impact in clinical practice.

Navigation may be an option to ensure secure screw placement, but it is essential to take into account several limitations associated with navigation, such as longer operation time, a steeper learning curve, increased expenses, and more complicated equipment. Furthermore, while the increase in accuracy achieved through navigation is statistically significant, its cost-effectiveness needs to be evaluated through a thorough cost-benefit analysis.

At present, the grading system for assessing pedicle screw accuracy that is most commonly used and acknowledged is the 2 mm increment grading system that relies on CT imaging. The majority of evaluation techniques rely entirely on imaging. Nonetheless, there is still no universally accepted and definitive method to determine the precision of pedicle screw placement in the realm of spinal surgery.

An all-encompassing grading system ought to comprise three elements:

  • the degree of deviation measured through imaging
  • the position of the deviation concerning critical anatomical landmarks
  • whether or not any associated clinical symptoms are present.


Methods to Determine Pedicle Screw Placement Accuracy

Numerous studies in the literature have utilized both the 2 mm increments and the in-and-out grading systems. It is evident that the majority of surgeons will employ imaging to evaluate the positioning of pedicle screws during and after the operation. Upon reviewing the literature, it was found that CT imaging is the most commonly employed technique for post-operative imaging.

The standard parameters of CT imaging, such as the thickness of the slices and the gantry tilt, have an impact on both the precision of imaging measurements and the degree of radiation exposure experienced by the patient. While gantry tilt is seldom altered, adjustments to the thickness of the imaging slices are more frequently made. To balance precision and patient safety by reducing radiation exposure, imaging with a thickness of 2mm is frequently employed.

Accurate postoperative assessment is essential to ensure successful outcomes and identify potential complications. Various methods are used to assess the accuracy of pedicle screw placement:

CT Scans

Computed tomography (CT) scans provide highly detailed images of the spine, allowing precise evaluation of screw position relative to the pedicle and surrounding structures. CT scans are considered the gold standard for postoperative assessment due to their accuracy and detail.


Radiographs, or X-rays, are useful for an initial assessment of screw placement. While they offer less detail than CT scans, they are quicker and more readily available, making them suitable for immediate postoperative checks.

Intraoperative Neuromonitoring

Intraoperative neuromonitoring involves monitoring the electrical activity in spinal nerves during surgery to detect potential nerve injury. This technique provides real-time feedback, helping surgeons avoid damaging nerves during screw placement.

The grading system that is most commonly utilized involves measuring the breach of pedicle screws in increments of 2mm. If the breach of the pedicle is less than 2mm, it is considered to be safe. While this grading system is deemed acceptable, it is important to take into account the location of the breach, particularly when determining the safety of a screw.

The in or out classification is the second most frequently utilized method for evaluating the placement of pedicle screws. While a small breach can be easily identified via imaging, it is important to distinguish its clinical significance from that of a larger breach. Therefore, this method is less effective in identifying whether a screw is positioned in a safe zone versus an unsafe one. What is crucial for precision and safety is the clinical significance of the breach.


The accurate placement of pedicle screws is critical for the success of spinal surgeries. Advanced techniques such as fluoroscopy guidance, navigation systems, and robotic assistance have significantly improved the accuracy of screw placement compared to the freehand method. Navigation systems and robotic assistance, in particular, offer high accuracy rates, with robotic systems representing the pinnacle of precision in spinal surgery.


Do you have more questions? 

What are pedicle screws?

Pedicle screws are medical devices used in spine surgery to provide stabilization and support by anchoring into the vertebrae.

Why is accurate pedicle screw placement important?

Accurate placement is crucial to avoid complications like nerve damage, spinal cord injury, and vascular injury, and to ensure the stability of the spine.

What is the freehand technique?

The freehand technique involves the surgeon placing screws based on anatomical landmarks and tactile feedback without real-time imaging.

How does fluoroscopy guidance work?

Fluoroscopy uses real-time X-ray imaging to guide the surgeon in placing screws, providing visual feedback to improve accuracy.

What are the benefits of using fluoroscopy in screw placement?

Fluoroscopy improves accuracy compared to the freehand method and helps in adjusting the screw trajectory during surgery.

What are the downsides of fluoroscopy guidance?

The main downside is the exposure to radiation for both the patient and the surgical team.

What are navigation systems in spine surgery?

Navigation systems use preoperative or intraoperative imaging to create a 3D model of the spine, guiding screw placement with high precision.

Why are navigation systems preferred over traditional methods?

They provide higher accuracy, reduce the risk of screw misplacement, and improve overall surgical outcomes.

What is robotic assistance in spine surgery?

Robotic systems use advanced navigation combined with robotic arms to place screws with extreme precision, following pre-defined paths.

How accurate is robotic-assisted screw placement?

Robotic systems achieve an accuracy rate of around 98.3%, making them the most precise method available.

What are the disadvantages of using robotic systems?

Robotic systems are very expensive, require significant setup time, and necessitate extensive training for the surgical team.

How does the accuracy of the freehand technique compare to other methods?

The freehand technique has the lowest accuracy, ranging from 69% to 94%, compared to higher rates with fluoroscopy and navigation systems.

What are the average accuracy rates for fluoroscopy and navigation systems?

Fluoroscopy has an average accuracy of 89%, while navigation systems average around 95%.

How are postoperative assessments of screw placement conducted?

Common methods include CT scans for detailed evaluation, radiographs for initial checks, and intraoperative neuromonitoring for real-time feedback.

Do navigation systems improve accuracy at all spinal levels?

Navigation systems significantly improve accuracy in most spinal levels, though their benefits at thoracic levels may be less pronounced.

Why are CT scans considered the gold standard for postoperative assessment?

CT scans provide highly detailed images, allowing precise evaluation of screw placement and identification of any inaccuracies.

Can navigation systems eliminate the need for fluoroscopy?

Navigation systems reduce the reliance on fluoroscopy but do not completely eliminate the need for real-time imaging in certain cases.

What role does intraoperative neuromonitoring play in screw placement?

It monitors the electrical activity in spinal nerves during surgery to detect potential nerve injury, providing real-time feedback to avoid damage.

What is the learning curve associated with robotic systems?

Surgeons experience a learning curve with robotic systems, but accuracy improves significantly with experience and practice.

Are there any specific complications associated with inaccurate screw placement?

Yes, complications can include nerve damage, spinal cord injury, vascular injury, and compromised spinal stability.

How does the cost of advanced techniques compare to traditional methods?

Advanced techniques like navigation systems and robotic assistance are significantly more expensive than traditional methods like the freehand technique.

What training is required for using navigation systems and robotic assistance?

Specialized training is required for both navigation systems and robotic assistance to ensure accurate and effective use during surgery.

How do surgeons choose the best method for screw placement?

Surgeons consider factors like the specific spinal level, the complexity of the case, available equipment, and their own experience and training.

What future advancements can we expect in pedicle screw placement?

Future advancements may include improved imaging techniques, more intuitive robotic systems, and further integration of AI to enhance precision and reduce errors.

Dr Vedant Vaksha

I am Vedant Vaksha, Fellowship trained Spine, Sports and Arthroscopic Surgeon at Complete Orthopedics. I take care of patients with ailments of the neck, back, shoulder, knee, elbow and ankle. I personally approve this content and have written most of it myself.

Please take a look at my profile page and don't hesitate to come in and talk.