Effect of Fixation Pin Insertion on the Bone-Pin Interface

Smooth and partially threaded 3.12 mm (1/8 inch) trochar-tipped Steinmann pins were inserted transversely through both diaphyseal cortices of eight mature canine tibias using five methods. Angular velocity (revolutions per minute) during insertion and temperature elevation due to friction during penetration of the second cortex were recorded. The force required for extraction of the pins from the bone and the histologic appearance of the bone-pin interface were determined for one-half of the pins 2 days after insertion and for one-half of the pins 56 days after insertion. The increase in temperature was similar for all methods of insertion except high speed power, which was significantly greater (p < 0.05). The force required for axial pin extraction was similar for pins inserted by hand chuck, predrilled, and low speed power methods after both 2 and 56 days. Pins inserted by high speed power and hand drill required force similar to the others for extraction after 2 days but significantly less force (p < 0.05) for extraction after 56 days. The partially threaded pins required significantly greater force (p < 0.01) extraction after both 2 and 56 days. Histologic examination revealed increased mechanical bone damage surrounding hand chuck inserted pins, increased bone necrosis surrounding high speed power inserted pins, and increased inflammatory changes surrounding hand drill inserted pins.