Biomechanical effects of point configuration in Kirschner-wire fixation

The drilling and bone holding properties of Kirschner wires of three different tip designs have been investigated. The tip designs studied were the commercially available trocar- and diamond-shaped tips and the homemade cut tip produced by cutting the pin obliquely with wire cutters. Thirteen canine metacarpals were drilled with wires of each tip design at 400 and 800 rpm. A servohydraulic test machine (Materials Test Systems, Minneapolis, MN) simultaneously measured axial loads, torque, and displacement during insertion and pull-out. Kirschner wires of each tip configuration were also placed in seven canine metacarpals for a three-week in vivo test. After the animals were killed, peak pull-out forces were measured and compared with in vitro results. The trochar-tipped wire displayed the highest required torque and axial load to penetrate bone. It also demonstrated the highest pull-out force immediately after drilling, especially when inserted at the low drill speed. After placement for three weeks, pull-out force of the diamond-tipped wire equaled the trochar. The homemade cut wire consistently yielded inferior holding properties. For immediate and sustained strong fixation in bone, a wire with a trochar tip configuration should be inserted at low drill speeds.