External fixator clamp reuse degrades clamp mechanical performance

Area of Science:

• Orthopedic biomechanics
• Biomaterials science
• Surgical instrumentation

Background:

• External fixator clamps are crucial for maintaining fracture reduction stability.
• The mechanical integrity of these clamps is essential for successful fracture healing.
• The impact of clamp reuse on mechanical properties is not fully understood.

Purpose of the Study:

• To evaluate the effects of clamp reuse on the mechanical properties of three common external fixator clamp types: Kirschner-Ehmer (KE), Securos, and IMEX-SK.
• To compare the degradation patterns among the tested clamp types.

Main Methods:

• An experimental bench test was conducted to assess the mechanical properties of 18 clamps of each type (KE, Securos, IMEX-SK).
• Six mechanical variables were tested: fixator pin slippage, connecting bar slippage, fixator pin rotation, connecting bar rotation, and clamp-bolt axis pivot (clockwise and counterclockwise).
• Each clamp underwent six repeated tests for each variable at a consistent clamp-bolt tightening torque of 7.68 Nm.

Main Results:

• All three clamp types exhibited degradation in at least one mechanical variable after reuse.
• The IMEX-SK clamp showed significant degradation in connecting bar slippage and fixator pin rotation, with an increased resistance to clockwise clamp-bolt axis pivot.
• The Securos clamp degraded significantly in connecting bar slippage, connecting bar rotation, and fixator pin rotation, while the KE clamp showed degradation only in connecting bar slippage.

Conclusions:

• Repeated use of external fixator clamps leads to degradation of their mechanical performance, affecting their ability to resist motion.
• The IMEX-SK and Securos clamps demonstrated greater susceptibility to degradation compared to the KE clamp.
• Clinicians should be aware of the potential for reduced fixator composite rigidity and unpredictable performance when reusing external fixator clamps.