Model of the behavior of a Kirschner-Ehmer style external fixator clamp

Several Kirschner-Ehmer style clamps used in external fixation of fractures were loaded in various configurations. The clamp was found to be characterized mechanically as a torsional spring, rather than a rigid connector between a sidebar and a bone pin. Also, the center of rotation is offset from the center of the bolt. Proper modeling of planar unilateral and bilateral fixator frames should be possible by treating the KE-style clamp as a torsional spring with a center of rotation displaced slightly toward the sidebar.