Does Resistance Indicate Malposition? A Standardized Comparison of Pedicle Screw Placement

Area of Science:

• Spine Surgery
• Biomechanical Engineering
• Surgical Navigation

Background:

• Pedicle screw malpositioning is a common complication in spinal fusion surgery, potentially necessitating revision.
• Real-time detection of malpositioning is desirable to improve surgical outcomes.
• Analyzing mechanical resistance and torque during screw insertion has been proposed as a potential method for detection.

Purpose of the Study:

• To evaluate the reliability of torque-based mechanical resistance for real-time detection of pedicle screw malpositioning.
• To compare torque values during drilling, tapping, and insertion between correct and malpositioned screw trajectories.

Main Methods:

• Utilized five fresh-frozen human thoracolumbar spine specimens.
• Employed 3D-printed templates to create correct and four defined malpositioned trajectories (medial, lateral, superior, superolateral) with offsets of 2.0-3.5 mm.
• Conducted drilling, tapping, and insertion at constant speed and feed force, measuring peak torque.

Main Results:

• No statistically significant differences in peak torque were observed between correct and malpositioned trajectories during tapping and insertion phases.
• Regional analysis of thoracic versus lumbar spine did not yield significant differences in torque.
• A statistically significant difference in torque was found only during the drilling phase between the correct trajectory and the superolateral malposition (p=0.038).

Conclusions:

• Under standardized conditions, torque-based mechanical resistance is generally not a reliable indicator for detecting pedicle screw malposition in real-time.
• Further research may be needed to explore alternative or refined methods for intraoperative malposition detection.