Biomechanical Comparisons of Unidirectional and Bidirectional Kirschner-Wire Insertion

Abstract

Peak axial loads on entry and peak pull-out loads were measured for Kirschner-wires (K-wire) inserted into canine metacarpals. The wires were placed using a standard, unidirectional drill and using an oscillating, bidirectional drill that reversed spin direction every 120 degrees. Seven trocar-tip wires were compared with seven diamond-tip wires using each drilling method. The trocar-tip wires demonstrated equal peak axial loads on entry when drilled at comparable speeds unidirectionally and bidirectionally. Pull-out load of the trocar tip after bidirectional insertion was less than that for unidirectional insertion but was still in the clinically useful range. The diamond-tip wire exhibited higher peak axial load on entry and lower peak pull-out load when drilled bidirectionally. Bidirectional insertion of a trocar-tip K-wire offers fixation characteristics comparable with those with unidirectional insertion and will potentially reduce the risk of soft-tissue damage associated with winding-up and avulsion of vital structures on the spinning shaft of a unidirectional driver.