Mechanical performance of the standard Orthofix external fixator

Area of Science:

• Orthopedics
• Biomedical Engineering
• Materials Science

Background:

• External fixators are crucial for bone fracture stabilization.
• Assessing the mechanical performance and reusability of external fixation devices is vital for patient outcomes and healthcare costs.

Purpose of the Study:

• To evaluate the static and fatigue performance of the Orthofix unilateral external fixator.
• To compare its mechanical properties against the Hoffmann-Vidal quadrilateral frame.
• To identify potential failure modes and reusability considerations.

Main Methods:

• Static and fatigue testing of the Orthofix unilateral external fixator.
• Comparison with the Hoffmann-Vidal quadrilateral frame under identical fixation.
• Cyclic loading (2 million cycles) and manual tightening/loosening cycles were applied.
• Mechanical properties (bending, torsional, axial stiffness) and wear were assessed.

Main Results:

• Orthofix demonstrated higher bending stiffness and equal torsional stiffness compared to the Hoffmann-Vidal frame.
• Axial stiffness was lower in the Orthofix device.
• Ball joint stiffness correlated with tightening torque.
• Significant stiffness degradation was not observed after 2 million cycles.
• Repetitive use led to abrasive wear, cam migration, and reduced locking strength (20-25%) after 50 cycles.
• Wear was also noted on screw threads.

Conclusions:

• The Orthofix external fixator exhibits robust mechanical properties but requires inspection and potential component replacement for re-use.
• Periodic tightening of the ball joint and fixation screws is necessary to maintain frame stiffness during clinical application.
• Design modifications are recommended to enhance the mechanical performance and durability of the Orthofix device.