ASTM F1798 – Standard Guide for Evaluating the Static and Fatigue Properties of Interconnection Mechanisms and Subassemblies Used in Spinal Arthrodesis Implants

This test method covers the measurement of uniaxial static and fatigue strength, and resistance to loosening of the component interconnection mechanisms of spinal arthrodesis implants.  The purpose of this test method is to provide a means of mechanically characterizing different designs of spinal implant interconnections. Ultimately, the various components and interconnections should be combined for static and fatigue testing of the spinal implant construct.  It is not the intention of this test method to address the analysis of spinal implant constructs or sub-constructs or to define levels of performance of spinal implants as insufficient knowledge is available to predict the consequences of the use of particular spinal implant designs.

Spinal implants are generally composed of several components that, when connected together, form a spinal implant construct.  Spinal implant constructs are designed to provide some stability to the spine while arthrodesis takes place.  This test method outlines standardized evaluations of different interconnection mechanisms to facilitate comparison between different designs.  Comparisons must be made cautiously and with careful analysis, taking into account the effects that design differences can have on the loading configurations.  This test method is used to quantify the static and fatigue properties of different implant interconnection designs.  The mechanical tests are conducted in vitro using simplified, unidirectional loads and moments.  Fatigue testing in a simulated body fluid or saline may have a fretting, corrosive, or lubricating effect on the interconnection and thereby affect the relative performance of tested devices.  Hence, the test environment, whether a simulated body fluid, saline (9g NaClper 1000 mL H2O), with a saline drip, or dry, is an important characteristic of the test and must be reported accurately.

The tulip pull-off test will soon be added to ASTM F1798.  Example of static test results are shown below.

ASTM F1798 Graph 1 - New

ASTM F1798 Graph 2

ASTM F1798 Graph 3

ASTM F1798 Graph 4

Photos of Test