External ring fixators: An overview

Abstract

External fixation is widely used in the fixation of fractures and limb deformities. The mechanical characteristics of a specific external fixator are major factors in determining the biomechanical environment at a fracture/osteotomy site and, hence, affect the healing process. Although the optimal biomechanical environment for healing of a fracture or an osteotomy is unknown, a specific range of interfragmentary motion exists which promotes healing. It is therefore desirable that the mechanics of an external fixator can be manipulated to enable the surgeon to control the range of interfragmentary motion. The characteristics of an external fixator are defined by a large number of variables. Therefore, to gain control over the degree of interfragmentary motion, an understanding of the effect of each variable and how it interacts with the others to determine the overall characteristics of the device is required. For the past two decades, individual components and whole-frame configurations have been studied in depth. This article provides a summary of previous work concerning the mechanics of external ring fixators and how they affect the biomechanical environment at the fracture/osteotomy site.

Circular external fixation in the management of tibial plateau fractures in patients over the age of 55 years

“…The resultant fixator exhibited decreased stiffness at higher loads and less axial and bending stiffness when compared to traditional Ilizarov circular external fixators. 28,29 This led to unwanted motion and the fracture site with resultant loss of reduction, non-union and increased pin-site infection rates. [30][31][32][33][34] Conventional circular external fixation, however, has recently emerged as a viable treatment alternative for bicondylar plateau fractures.…”

“…Biomechanical analysis also demonstrated that the use of four tensioned olive wires combined with a single lag screw provided adequate stability when compared to dual plating. 28 The aim of this study was to compare the complication and union rate of tibial plateau fractures treated by circular external fixation in patients older than 55 years with that achieved in younger patients. While we would like to believe that a 55-year-old person should not be classified as elderly, we used this figure as it is in line with previously published reports.…”

Analytical modelling of Kirschner wires in Ilizarov circular external fixator as pretensioned slender beams

“…Thus, the FEA in the present study can be used to verify the analytical solutions as given in §3. Watson et al (2000Watson et al ( , 2003b have published the results from their experimental work for displacements of a K-wire (DZ180 mm and dZ1.8 mm) loaded perpendicular to its longitudinal axis at its midpoint, under different pretensions, in two graphs ( fig. 5 of Watson et al 2000Watson et al , 2003b.…”

“…Watson et al (2000Watson et al ( , 2003b have published the results from their experimental work for displacements of a K-wire (DZ180 mm and dZ1.8 mm) loaded perpendicular to its longitudinal axis at its midpoint, under different pretensions, in two graphs ( fig. 5 of Watson et al 2000Watson et al , 2003b. The results in figure 8 of this paper, which are based on the analytical solutions, are comparable with the results shown in either of those graphs.…”

Reconstructive surgery of the human tibia by use of external ring fixator and the Ilizarov method

“…The ideal characteristics of a ring fixator with ability to accomodate variable stiffness to optimize the healing process at all stages of treatment should according to Watson et al (2000) be:…”