THE EFFECT OF STAPLE SIZE, ORIENTATION, AND NUMBER ON TORSIONAL FRACTURE FIXATION STABILITY

Staples have been used for fixation of metaphyseal fractures, but ther e are no guidelines for placing the staples to ensure maximum fixation stability. This study investigated the effect of staple size, orienta tion, and number on torsional stability in simulated transverse fractu res. Six homogeneous foam cylinders were cut transversely, stapled bac k together using a power driver, and rotated coaxially on a servohydra ulic 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 perfo rmed seven times. Torsional holding power was increased when two stapl es were oriented in opposite directions (45-degrees) and had bridges w ide 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; furt her significant increases were also observed for the use of three, fou r, and five staples. Bridge width and leg length had minimal effect, a s long as bone purchase sufficient to avoid cutout was maintained from the staple to the fracture surface.