Mechanical testing of the wire clamping characteristics of the Fixclip™ internal fixation system

Abstract

Stainless steel wires (Kirschner's wires) have been used for over 60 years to fix internally a wide range of osteotomies and fractures in bones. Fixclips™ (Corifix, Cirencester, UK) shaped like winged washers have been used to clamp pairs of K wires of diameters ranging from 0.8 to 3.0mm to standard orthopaedic screws and to fix bones internally in more than 400 patients. The system has proved to be biologically and mechanically very effective. This paper describes the design and some biomechanical test results of the Fixclip™. Preliminary strength tests conducted using a Hounsfield Tensometer show that the pull-out force, reflecting the grip of the clip on the wire, is dependent on the wire size and, throughout the clinically relevant range, increases linearly with increasing screw torque. Changing the surface finish of the clip did not confer any advantage over the existing polished clip in terms of grip strength.