Relationship between locking-bolt torque and load pre-tension in the Ilizarov frame

Area of Science:

• Orthopedic biomechanics
• Surgical device engineering

Background:

• Ilizarov frames are essential for treating complex fractures.
• Proper assembly is critical for frame stability and patient outcomes.
• The mechanical behavior of the wire-bolt interface under physiological loading is not fully understood.

Purpose of the Study:

• To mechanically test the wire-bolt interface in Ilizarov frames.
• To define the optimal locking-bolt torque for Ilizarov frames during physiological loading.
• To investigate the effect of locking-bolt torque on wire pre-tension and frame stiffness.

Main Methods:

• Mechanical testing of the wire-bolt interface using a simulated bone model (copper tube).
• Application of varying locking-bolt torques (up to 14 Nm and beyond).
• Analysis of force-displacement curves and wire pre-tension loss.
• Microscopic examination of wire damage.

Main Results:

• Ilizarov wire force-displacement curves are unaffected by locking-bolt torque.
• Optimal pre-tension is maintained up to 14 Nm; higher torques lead to pre-tension loss.
• Low and high torques result in poor wire holding and plastic deformation, respectively.
• Wire damage was observed under microscopy at varying torque levels.

Conclusions:

• 14 Nm is identified as the optimal locking-bolt torque for Ilizarov frames.
• Deviations from optimal torque compromise frame stability and may impede fracture healing.
• Precise assembly is crucial to prevent complications like delayed union.