STP1559

    Bending Fatigue Characteristics of Orthopedic Biomaterials

    Published: Sep 2013


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    Abstract

    The overall mechanical properties of titanium and stainless steel biomaterials are well known, but a review of the literature indicates that comparing their biomechanical fatigue performance may be application dependent and is often evaluated at high cycle counts up to 10 × 106 cycles or more. The purpose of this study was to utilize a standardized methodology to compare the bending fatigue performance of 316L stainless steel (SS) and Ti-6Al-4V (Ti) orthopedic trauma implants in a trauma device lifecycle scenario of no more than 1 × 106 cycles. 1 × 106 loading cycles represents approximately 1 year in vivo that is the typical utility life of a trauma device, because healing would be expected in this time frame. Cannulated rods, made of either SS or Ti, were prepared, all of which incorporated a transverse hole that simulated the distal geometry of an intramedullary nail. Based on ASTM F1264-03 Standard Specification and Test Methods for Intramedullary Fixation Devices, the specimens were tested by applying multiple force levels using four-point bending, sinusoidal-wave, cyclical fatigue until failure, or run-out at 1 × 106 cycles occurred. Various force levels were utilized during testing to evaluate the trend between stress levels (range: 480–2200 MPa) versus fatigue life. On average, the SS specimens survived longer than the Ti specimens at greater stress levels and the Ti specimens survived longer than the SS specimens at lesser stress levels. This study shows that fatigue life comparisons among trauma intramedullary nails may not only be design dependent, but is also governed by the relationship between expected in vivo lifetime and stress level. Therefore, understanding the clinical indications and intended uses are critical in the decision to use either material for orthopedic trauma applications.

    Keywords:

    biomechanics, trauma, stainless steel, titanium, mechanical testing


    Author Information:

    Whitten, Andy
    Smith & Nephew, Inc., Memphis, TN

    Cartner, Jacob
    Smith & Nephew, Inc., Memphis, TN

    Soileau, Ramona
    Smith & Nephew, Inc., Memphis, TN


    Paper ID: STP155920120204

    Committee/Subcommittee: E08.05

    DOI: 10.1520/STP155920120204


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