Mechanical considerations in using tensioned wires in a transosseous external fixation system.

Factors that affect wire tension were examined using external mechanical testing units as well as in-line load cells. The circular external fixator with wires supported at each end exhibits a self-stiffening effect such that wire stiffness increases with wire deflection. Mechanical slippage between wire and fixation bolt is the primary reason for loss of wire tension. Slippage can be avoided by adequate torque on the fixation nut (20 N.m). Guidelines are presented for proper and safe tensioning techniques to achieve clinically indicated tensions without risk of breakage.