
Abstract
The relative stiffness of five different external wrist fixators currently in use for distal radius fractures was determined using a uniform fracture model consisting of wood dowels to isolate the effects of the fixators themselves. Each construct was loaded in axial compression, eccentric and cantilever modes of bending, and torsion. The stiffest of the fixators varied by a factor of three in compression, five in bending, and three in torsion. Although the ideal stiffness of a wrist fixator is unknown, there is a large variation in the stiffness of existing devices.
**********
Fractures of the distal radius are common injuries and were described clinically as early as 1814 by Colles. (1) Low energy distal radius fractures are usually treated by closed means, while higher energy injuries often require internal or external fixation. Many different types of external fixators have been designed and are currently in use. To date however, no consensus has been reached regarding the optimal fixator for management of distal radius fractures. It is thought that a stiff external fixator promotes primary fracture healing while a less rigid device promotes more of a secondary fracture healing. The optimal rigidity required to maintain the reduction in a distal radius fracture is not known. (2-7) Previous biomechanical comparison studies of these fixators have demonstrated a wide range of fixator stiffness. (6,8,9,10-12)
The purpose of this study was to evaluate the relative stiffness of five currently used external fixator frames under standardized loading conditions. In addition to determining stiffness in axial compression (AC), torsion (T), and anterior (AB-M), posterior (PB-M), medial (MB-M), and lateral (LB-M) eccentric bending moments, our study also tested stiffness in cantilever anterior (AB-C), posterior (PB-C), medial (MB-C), and lateral (LB-C) bending. By superposition, it is then possible to calculate the fixator stiffness in any complex loading mode. The model used in this study was designed purely to allow loading in the above standardized conditions to evaluate the relative stiffness of each fixator and does not exactly replicate distal radius or Colles type fracture.
Materials and Methods
Five external fixators were tested (Fig. 1): Synthes Distal Radius Fixator (Synthes, Paoli, PA), Yellow Monotube …