A new alternative to expandable pedicle screws: Expandable poly-ether-ether-ketone shell

Area of Science:

• Spinal surgery
• Biomaterials science
• Orthopedic biomechanics

Background:

• Pedicle screw fixation in the sacrum is prone to pullout due to high cyclic micromotions and poor bone quality.
• Existing expandable screws have limitations that this study aims to overcome.
• Sacral fixation challenges necessitate innovative solutions for improved implant stability.

Purpose of the Study:

• To biomechanically compare a newly designed poly-ether-ether-ketone (PEEK) expandable shell with classical pedicle screws.
• To evaluate the pullout strength and fatigue performance of the PEEK expandable shell system.
• To determine the mechanical viability of the PEEK expandable shell as a safer alternative for sacral fixation.

Main Methods:

• Biomechanical testing including torsion, pullout, fatigue, flexion/extension moment, axial, and torsional gripping capacity tests.
• Testing conducted on polyurethane foam and calf vertebrae models according to ASTM standards (F543, F1798, F1717).
• Comparison of pullout loads and endurance limits between the PEEK expandable shell and classical pedicle screws.

Main Results:

• The PEEK expandable shell demonstrated significantly higher pullout loads (33-53% increase) compared to classical pedicle screws in both polyurethane foam and calf vertebrae.
• The PEEK shell exhibited superior endurance at 90% of its yield load, versus 70% for classical screws.
• Fatigue performance was enhanced with the PEEK shell due to its capacity to dampen micromotions.

Conclusions:

• The expandable PEEK shell offers substantially improved pullout performance and mechanical stability over classical pedicle screws.
• The PEEK expandable shell demonstrates superior fatigue resistance, crucial for long-term sacral fixation.
• The PEEK expandable shell presents a mechanically safe and effective alternative to existing expandable pedicle screw systems for sacral fixation.