The effect of staple size, orientation, and number on torsional fracture fixation stability

Staples have been used for fixation of metaphyseal fractures, but there are no guidelines for placing the staples to ensure maximum fixation stability. This study investigated the effect of staple size, orientation, and number on torsional stability in simulated transverse fractures. Six homogeneous foam cylinders were cut transversely, stapled back together using a power driver, and rotated coaxially on a servohydraulic test system. Staples with bridge widths of 7, 10, 13, and 16 mm, and leg lengths of 7, 10, 15, and 20 mm were used. Each test was performed seven times. Torsional holding power was increased when two staples were oriented in opposite directions (45 degrees) and had bridges wide enough to maintain bone purchase with respect to the fracture line. Fixation effectiveness increased with the number of staples: the use of two staples (as opposed to one) yielded the biggest increase; further significant increases were also observed for the use of three, four, and five staples. Bridge width and leg length had minimal effect, as long as bone purchase sufficient to avoid cutout was maintained from the staple to the fracture surface.