COMPARISON OF THE MECHANICAL PERFORMANCE OF 3 TYPES OF EXTERNAL FIXATORS - LINEAR, CIRCULAR AND HYBRID

Different configurations of the Monticelli-Spinelli and llizarov exter nal fixation systems were tested to define their mechanical properties . In five configurations the external fixator consisted of rings with tensioned wires (circular), while in one configuration two pairs of th e tensioned wires and their correspondent ring were replaced by thread ed pins (hybrid). Testing was performed in axial compression, bending and torsion. The results were compared to the characteristics of a sel ected linear fixator group. Both the circular and the hybrid configura tions were non-linear in compression. In bending, circular fixators ha d a similar pattern in both anteroposterior and oblique loading direct ions. The bending load-displacement pattern for the hybrid fixators wa s similar to the linear fixators, higher stiffness in the plane of the pins. Torsion was linear for both circular and hybrid fixators, as fo r the linear fixators. By combination of wires and pins (hybrid config uration), the mechanical behaviour had characteristics from both linea r and circular fixators. it is concluded that the three studied groups own different mechanical performance and can be considered as differe nt types of fixators. While it has been demonstrated that osteogenesis can be achieved independently of the mechanical behaviour of the fixa tor, this study supports the suggestion that some complications can be related to the mechanical behaviour of the fixator. Relevance-This st udy provides some guidelines for selecting the appropriated external f ixator for clinical use depending upon the stiffness requirements of a specific clinical case. Furthermore, the information on the mechanica l characteristics of the different systems of external fixation permit s some conclusions on the possible failures of the fixators during the ir clinical application. However, the mechanical differences observed cannot be utilized to support differences on the biology of the fractu re or osteotomy foci where these types of fixators are used.