Assessment of the tolerance angle for pedicle screw insertion

Area of Science:

• Orthopedic Surgery
• Biomedical Engineering
• Surgical Robotics

Background:

• Pedicle screw insertion requires precise cannulation, a step influenced by surgeon experience.
• Variability in bone quality can affect surgical tool behavior during cannulation.
• A standardized method is needed to characterize tool-bone interaction.

Purpose of the Study:

• To develop and validate a reliable experimental protocol for characterizing surgical tool slippage during the cannulation process.
• To assess the influence of synthetic bone density on cannulation parameters.
• To identify key metrics for predicting perforation during pedicle screw insertion.

Main Methods:

• Utilized an MTS Acumen 3 A/T device with a Kistler load cell for a three-step cannulation test on synthetic bone samples.
• Tested three foam densities at a constant rotational speed (10° mm⁻¹) and varying cannulation angles (10°–30°).
• Scanned samples post-test to compute cannulation coefficients and analyzed force data.

Main Results:

• Developed a reproducible protocol with high intraclass correlation coefficients (ICC) for synthetic bone samples (Sawbone: 0.979, Creaplast: 0.909).
• Cannulation coefficient and maximum Z-axis force effectively describe perforation.
• An angular threshold of 17.5° predicted perforation with 89.5% area under the ROC curve.

Conclusions:

• The developed protocol reliably characterizes surgical tool slippage during cannulation.
• Identified critical parameters and an angular threshold for predicting perforation, independent of surgeon experience.
• This method can help optimize pedicle screw insertion based on bone quality assessment.