Primary Experimental Feedback on a Co-manipulated Robotic System for Assisted Cervical Surgery

Robotic-assisted surgery has emerged as a promising approach to improve surgical ergonomics, precision, and workflow efficiency, particularly in complex procedures such as cervical spine surgery. In this study, we evaluate the performance of a collaborative robotic system designed to assist surgeons in drilling tasks by assessing its accuracy in executing predefined trajectories. A total of 14 drillings were performed by eight experienced cervical surgeons, utilizing a robotic-assisted setup aimed at ensuring stability and alignment. The primary objective of this study is to quantify the deviations in the position and orientation of the drilling tool relative to the planned trajectory, providing insights into the system’s reliability and potential impact on clinical outcomes. While the primary function of robotic assistance in surgery is to enhance surgeon comfort and procedural guidance rather than solely optimizing precision, understanding the system’s accuracy remains crucial for its effective integration into surgical practices part of this primary experimental feedback, the study offers an in-depth analysis of the co-manipulated robotic system’s performance, focusing on the experimental setup and error evaluation methods. The findings of this study will contribute to the ongoing development of robotic-assisted cervical surgery, highlighting both its advantages and areas for improvement in achieving safer and more efficient surgical workflows

💡 Research Summary

This paper presents an experimental evaluation of a collaborative robotic system designed to assist surgeons during cervical spine drilling, a critical step in pedicle screw placement. The hardware platform consists of a Franka Emika Panda robot (seven degrees of freedom) equipped with a 3 mm drill bit, a patient‑specific 3‑D printed cervical model (C2–C7) fabricated from PC‑ABS, and an OptiTrack V120 motion‑capture system operating at 120 Hz to track both the robot and the vertebral model.

Eight experienced cervical surgeons performed a total of sixteen drilling attempts on the model; fifteen trials yielded usable data and were considered successful. The experimental workflow required the surgeon to select a vertebra and the side of entry, after which the robot autonomously aligned its end‑effector with a pre‑planned entry‑exit trajectory defined during the pre‑operative planning stage. Surgeons could then fine‑tune the entry point while the robot maintained its orientation. Once confirmed, the robot locked all degrees of freedom except translation along the drilling axis, retracted the drill by ~3 cm, and then advanced it 15 mm into the bone. Throughout the procedure, the robot’s internal joint sensors and the external OptiTrack system recorded joint states, tool‑tip positions, and interaction forces/torques.

Error quantification was performed in two complementary ways. Positional error was defined as the Euclidean distance between the instantaneous drill tip and its orthogonal projection onto the intended trajectory, thereby capturing deviations perpendicular to the path—those most detrimental to screw placement accuracy. Orientation error was computed from the quaternion representing the rotational difference between the actual tool direction and the planned direction; the skew‑symmetric part of the resulting rotation matrix yielded a three‑component error vector and the associated rotation angle. All data were transformed into a common vertebra reference frame before analysis.

The results show that the system achieves sub‑millimetre positional accuracy and sub‑degree angular accuracy, both well within clinically acceptable limits (typically ≤1–2 mm and ≤2–3° for pedicle screw insertion). Median position errors were –0.1 mm (X‑axis), ≈0 mm (Y‑axis), and 0.2 mm (Z‑axis). Median angular error was about 0.5°. However, the analysis revealed axis‑specific performance characteristics: the X‑axis exhibited the highest external forces and the largest angular error, indicating lower rotational stiffness; the Y‑axis showed minimal forces but comparatively larger translational error, reflecting higher compliance; the Z‑axis displayed balanced behavior. These patterns are consistent with the intentional compliance of serial collaborative robots, which prioritize safe human‑robot interaction over rigid precision.

Clinically, the measured errors suggest that the robot can reliably guide surgeons, reducing hand tremor and maintaining the planned trajectory throughout drilling. Nonetheless, the reduced rotational stiffness along the X‑axis could become a limitation in anatomically constrained scenarios where fine angular adjustments are critical. The authors propose several avenues for improvement: mechanical reinforcement of the robot’s joints, implementation of higher‑bandwidth force/torque feedback control, and validation on anatomically realistic cadaveric specimens. Future work will also include a direct comparative study between manual and robot‑assisted drilling to quantify benefits in operative time, radiation exposure, and risk of neurovascular injury.

In summary, this primary experimental study demonstrates that a collaborative robot can provide clinically acceptable guidance for cervical spine drilling, highlights specific mechanical and control‑related weaknesses, and outlines a clear roadmap for further development and eventual clinical translation.