History and Evolution of Hexapod External Fixators

Abstract

Hexapod external fixators are the application, in medicine, of industrial parallel manipulators. The first attempts to create parallel manipulators for industrial purposes, date back to the beginnings of the twenty-first century, when several patents for industrial prototypes were released. However, it was only in 1949 that V.E. Gough created the first parallel manipulator with an octahedral configuration, that is, the modern hexapod fixator configuration, in order to test tyres with six degrees of freedom. Later, K. Cappel modified Gough’s original project (Gough-Cappel platform). In 1965, thanks to D. Stewart’s manuscript on a flight simulator platform, the parallel manipulator with six degrees of freedom became known worldwide. The theoretical basis behind the parallel manipulators can be dated back to the fifteenth century; since then, several mathematicians and philosophers became interested in the study of polyhedra (Mozzi, Chasles, Poinsot, Eulero, Ball), their theorems becoming the fundamentals of modern kinematics. The first clinical usage of hexapod fixators in medicine was in 1995, when J.C. Taylor introduced his “Taylor Spatial Frame,” to perform complex limb deformity correction. Many hexapod fixators have been since introduced 1995, not all based on the Gough-Cappel platform.