Mechanical evaluation of transosseous wire rope configurations in a large animal external fixator.

The research article details the designing and testing of an external skeletal fixator for large animals like horses and cattle. The innovative design uses wire ropes as a transosseous component for the repair of long bone fractures, and explores various methods to safely and effectively introduce pretension into the ropes.

Design and Testing of the External Skeletal Fixator

The researchers developed an external skeletal fixator intending to mend significant bone fractures in large animals. Utilizing theoretical methods, they aimed for determining the optimal size of fixator components. However, they discovered that

• Standard methods used to analyze the displacement of the transosseous component may not be applicable for wire ropes.
• Large pretensions are required in the wire ropes to achieve functional stiffness appropriate for fracture fixation.

Terminating Wire Ropes and Testing Tension to Failure

An important stage in their research was establishing a method to terminate the wire ropes. The end goal was to induce suitable pretension through the rope’s interaction with the fixator rings. This process involved:

• Termination of ropes using five different methods including three varieties of copper sleeves, welded ends, and drum sockets.
• Testing each termination method under axial tension until failure to assess their strength.
• Findings showed that drum sockets exceeded the strengths provided by the other methods with 57.6% of rope breaking strength, followed by welded ends with 44.3%, and copper sleeves ranging between 8.5 to 26.6%.

Wire Rope Configurations and Fixator Stiffness Evaluation

After establishing the most effective termination method, the researchers explored the wire rope configurations on the fixator:

• Five distinct rope configurations were assembled to the fixator, using wood blocks to simulate bones with gap defects.
• Each configuration was then loaded with axial compression, and stiffness was evaluated based on measured axial displacement and applied load.
• The research identified that a 4-ring fixator configuration with two ropes at 60 degrees angular separation per ring demonstrated the greatest stiffness.
• In worst-case scenario models, this configuration could withstand a mean axial compression load of 1,730 N at 2 mm of displacement.