Structural properties of a new design of composite replicate femurs and tibias

The purpose of this study was to compare the structural properties of a new vs. established design of composite replicate femurs and tibias. The new d esign has a cortical bone analog consisting of short-glass-fiber-reinforced (SGFR) epoxy, rather than the fiberglass-fabric-reinforced (FFR) epoxy in the currently available design. The hypothesis was that this new cortical b one analog would improve the uniformity of structural properties between sp ecimens, while having mean stiffness values in the range of natural human b ones. The composite replicate bones were tested under bending, axial, and t orsional loads, in general, the new SGFR bones were significantly less stif f th;ln the FFR bones, although both bone designs reasonably approximated t he structural stiffnesses of natural human banes. With the exceptions of th e FFR bone axial tests, the highest variability between specimens was 6.1%. The new SGFR bones had similar variability in structural properties when c ompared to the FFR bones under bending and torsional loading, bur had signi ficantly less variability under axial loading. Differences in epiphyseal ge ometry between the FFR and SGFR bones, and subsequent seating in the testin g fixtures, may account for some of the differences in structural propertie s: axial stiffness was especially dependent on bone alignment. Stiffness va riabilities for the composite replicate bones were much smaller than those seen with natural human bones. Axial strain distribution along the proximal -medial SGFR femur had a similar shape to what was observed on natural huma n femurs by other investigators, but was considerably less stiff in the mor e proximal locations. (C) 2001 Elsevier Science Ltd. All rights reserved.