Biomechanical comparison of hybrid external fixators

Area of Science:

• Orthopedic biomechanics
• Trauma surgery
• Biomaterials engineering

Background:

• Tibial fractures, particularly OTA 41-C proximal metaphyseal and shaft types, require stable fixation.
• Hybrid external fixators offer an alternative to conventional methods, but their biomechanical properties need thorough evaluation.

Purpose of the Study:

• To assess and compare the stiffness characteristics of four different hybrid external fixators against the conventional Ilizarov fixator.
• To evaluate the impact of connector placement on fixator rigidity.

Main Methods:

• Five composite tibiae were instrumented with four types of hybrid external fixators (Synthes, ACE Fischer, Howmedica Monticelli-Spinelli, Smith & Nephew Trauma Ilizarov) and a conventional Ilizarov fixator.
• Fixators underwent mechanical testing under axial compression, bending (anterior/posterior, medial/lateral), and torsion using a materials testing machine.
• Stiffness was quantified by analyzing load-deformation and torque-angle data.

Main Results:

• The Synthes and Monticelli-Spinelli fixators exhibited the highest rigidity when wire-to-ring connectors were positioned internally.
• Fixator stiffness varied by loading mode, being greatest in axial compression and lowest in posterior bending.
• Wire length was identified as a significant factor influencing overall fixator stiffness.

Conclusions:

• The tested hybrid external fixators, in their standard configurations, provide stiffness comparable to the conventional Ilizarov fixator for treating proximal tibial fractures.
• These findings support the use of hybrid external fixators as a viable option for managing complex tibial shaft and metaphyseal fractures.