Mechanics of struts in the Taylor Spatial Frame.

Abstract

Taylor Spatial Frame (TSF) is a hexapod circular external fixator, i.e. built with six struts connecting two rings to support bone fragments by fixating them to the rings by wires or pins. Struts are length adjustable and have universal joints (U-joints) at both ends which attach to the rings. Behaviour of struts is crucial to the biomechanics of the TSF. However, no study on struts' mechanical characteristics has been reported. In this work, TSF struts and their components and pieces of materials were tested and their mechanical properties are reported. For doing so, the followings tests were conducted: 1) three sizes of TSF Fast-FX struts at different lengths in axial compression, 2) three short struts in oblique compression, 3) two long struts, gripped at and after their U-joints, in axial tension, and 4) two pairs of separated U-joints in compression. Pieces of the strut body and threaded rod were also machined out and tested for material properties. All tests continued till failure and their load-deflection data are plotted. Curve-fitting was applied to the plot of the average load-deflections (of strut sizes at their minimum length). The stiffness characteristics, buckling failure loads and failure load of the universal joints are also reported. Results show that the preponderance of deflections occurs in universal joints, which makes the results relevant to all strut types using the same U-joints.