External fixator pin design

Area of Science:

• Orthopedic biomechanics
• Biomaterials engineering
• Surgical implant design

Background:

• External fixation systems are crucial for bone fracture stabilization.
• Pin loosening in cancellous bone is a common failure mode, leading to instability and infection.
• Optimizing the bone-pin interface is essential for robust external fixation.

Purpose of the Study:

• To systematically evaluate thread design features for improved bone-pin interface strength in cancellous bone.
• To identify critical design parameters that enhance the pullout strength of external fixation pins.
• To inform the design of next-generation external fixation pins with superior bone integration.

Main Methods:

• A systematic study of 5 mm self-tapping half pins with varying pitch, tooth profile, and minor diameter.
• Coaxial pullout testing was performed on fresh bovine cancellous bone.
• Evaluation of five commercially available external fixator pins to compare real-world performance.

Main Results:

• A significant increase in pullout strength was observed with a decrease in the minor diameter of the fixation pin.
• No statistically significant differences in pullout strength were found based on thread profile or pitch.
• Pins with larger interference fit demonstrated superior pullout strength in commercially available options.

Conclusions:

• Reducing the minor diameter of external fixation pins significantly enhances their holding power in cancellous bone.
• A larger interference fit, within acceptable limits for torsional strength, is recommended for optimal cancellous bone pin application.
• Current external fixation pin designs may not fully exploit the potential for enhanced bone-pin interface strength.