Mechanical Properties of Küntscher Nail Sections

Abstract

The purpose of this study was fourfold: determine the section rigidity in torsion and bending of three commonly used sizes of Küntscher-type nails obtained from a single source; compare the results with calculated values based on section geometry and material properties; determine the effect of a transverse hole (intended to accommodate a locking device) on section properties; and determine the effect of simulated-use cyclic loading on properties of sections with transverse holes. Because rods of this design are slotted and asymmetrical in cross section, bending tests were performed in two orientations, 0 deg (slot-down) and 90 deg (slot rotated 90 deg from the slot-down position). We found that the change from an 11-mm to a 15-mm rod diameter increased rod stiffness and strength by about a factor of two, except in the 90-deg orientation, where closure of the rod open section under load markedly reduced strength and stiffness for all rod sizes. Neither the transverse holes nor cyclic load exposure had a marked effect on section properties. In torsion, measured stiffness essentially equaled calculated stiffness. There was not a similar equality in measured and calculated stiffness in bending because the point loading in the actual tests produce much different effects on open sections than the pure bending moments used in the calculations. We also concluded that ASTM F 383 needs to be modified to incorporate a more conventional use of terminology for structural stiffness or rigidity and strength, and a method for measuring deflections that recognizes the problem of open sections. It also seems appropriate to modify the gripping method for torsion tests to include the use of mechanical chucks.