Fatigue performance of external fixator pins

Area of Science:

• Orthopedic biomechanics
• Biomaterials engineering
• Medical device design

Background:

• External fixators are crucial in orthopedic trauma and reconstruction.
• Pin fatigue failure can lead to construct instability and treatment complications.
• Understanding stress concentration in fixator pins is vital for improving device longevity.

Purpose of the Study:

• To assess the fatigue performance of commonly used external fixator pins.
• To quantify stress concentration effects at pin threads and other features.
• To identify design modifications that enhance pin fatigue strength.

Main Methods:

• Cyclic bending fatigue tests were performed on various external fixator pin types.
• A strength reduction factor (SRF) was calculated to evaluate stress concentration.
• Comparison of fatigue performance between smooth, threaded, and modified pin regions.

Main Results:

• Half pins exhibited significantly higher SRF values compared to full pins due to smaller thread root diameters.
• Finer threads and cold rolling processes demonstrated potential to increase pin fatigue strength.
• Depth markers and self-tapping fluted regions were identified as critical stress concentration sites.

Conclusions:

• Certain half pins may be susceptible to fatigue fracture under severe clinical loading.
• Pin design features, including thread characteristics and manufacturing processes, critically influence fatigue life.
• Further research into optimized pin designs is warranted to mitigate fatigue failure risks.