Mechanical comparison of two external fixator clamp designs

Area of Science:

• Orthopedic biomechanics
• Biomaterials and implant design
• Surgical instrumentation

Background:

• External fixation devices are crucial for stabilizing bone fractures.
• The security of fixation pin-clamp interfaces directly impacts construct rigidity.
• Existing clamp designs may have limitations in resisting pin migration under load.

Purpose of the Study:

• To evaluate and compare the performance of two external fixator clamp designs.
• To quantify the ability of each clamp to resist fixation pin movement.
• To assess the influence of tightening torque on clamp stability.

Main Methods:

• Mechanical testing of two external fixator clamp designs (Kirschner-Ehmer and an experimental design).
• Fixation pins were subjected to controlled loads to measure resisting forces at varying clamp bolt torques (4.4, 6.1, 7.8 Nm).
• Load/displacement curves were analyzed using nonlinear regression, with plateau and rise coefficients compared via ANOVA.

Main Results:

• The experimental clamp design prevented pin slippage at 7.8 Nm, unlike the Kirschner-Ehmer clamp which showed slippage at all tested torques.
• At 7.8 Nm, the experimental clamp exhibited only slight plastic deformation, while the Kirschner-Ehmer clamp and bolt showed bending.
• Increasing clamp bolt torque significantly improved resistance to pin movement for both designs.

Conclusions:

• The experimental external fixator clamp offers superior security against fixation pin movement compared to the Kirschner-Ehmer type.
• The new clamp design enhances overall construct rigidity and offers improved clinical design features.
• This clamp design is recommended for greater stability in external fixation applications.