Comparative Biomechanical Evaluation of Acrylic- and Epoxy-Pin External Skeletal Fixation Systems with Two- and Three-Point Fixation per Segment under Compressive Loading

摘要

The objective of the present study was to compare the mechanical strength of different designs of acrylic– and epoxy–pin external skeletal fixation (ESF) systems (comprising of both two–point and three–point fixation system per segment) under compressive loading. Group A comprised of constructs (n=32) with two–point fixation per segment and group B included constructs (n=32) with three–point fixation per segment. Four different designs viz., uniplanar, multiplanar–I, multiplanar–II and circular were developed using dental acrylic and epoxy putty (n=4 for each construct type) using ultra high density polyethylene rods, keeping a gap of 5 mm between the proximal and distal segments to simulate a fracture condition. The fixator constructs were then subjected to in vitro compressive loading @ 3 mm/min until failure using a Universal Testing Machine. The fixator constructs were evaluated based on compressive stress, strain, stiffness and modulus of elasticity. It was observed that the constructs with three–point fixation per segment were significantly stronger than constructs with two–point fixation. Both acrylic– and epoxy–pin ESF were sufficiently strong with no significant difference between them; among the different designs, uniplanar constructs were the weakest and circular constructs were the strongest. It can be concluded that the number of pins used and the plane in which the pins passed are the major factors contributing to fixation stability, without any difference between the materials used to construct the fixator