THE DESIGN AND PERFORMANCE OF AN EXPERIMENTAL EXTERNAL FIXATOR WITH VARIABLE AXIAL STIFFNESS AND A COMPRESSIVE FORCE TRANSDUCER

A unilateral external fixator has been designed for controlled experim ents into the effects of micromovement on fracture healing. The experi mental model used is based on a diaphyseal osteotomy of the right tibi a of the sheep. The main bar has linear bearings, which allows free ax ial movement. This is then controlled by a spring whose stiffness can be varied. The resulting axial micromovement can be calculated from th e measured compressive force and the known axial stiffness of the fixa tor. The transducer has limits of error of +13.3 N and -44.5 N. Prelim inary measurements showed maximum micromovement at the fracture site o f 0.48 mm during slow walking. (C) 1997 IPEM Published by Elsevier Sci ence Ltd.