ASTM F2077 – Test Methods For Intervertebral Body Fusion Devices

This test method covers the materials and methods for the static and dynamic testing of intervertebral body fusion device assemblies, spinal implants designed to promote arthrodesis at a given spinal motion segment.  This test method is intended to provide a basis for the mechanical comparison among past, present, and future nonbiologic intervertebral body fusion device assemblies.  This test method allows comparison of intervertebral body fusion device assemblies with different intended spinal locations and methods of application to the intradiscal spaces.  This test method is intended to enable the user to compare intervertebral body fusion device assemblies mechanically and does not purport to provide performance standards for intervertebral body fusion device assemblies.

Intervertebral body fusion device assemblies are generally simple geometric-shaped devices which are often porous or hollow in nature.  Their function is to support the anterior column of the spine to facilitate arthrodesis of the motion segment.  This test method outlines materials and methods for the characterization and evaluation of the mechanical performance of different intervertebral body fusion device assemblies so that comparisons can be made between different designs.  This test method is designed to quantify the static and dynamic characteristics of different designs of intervertebral body fusion device assemblies.  These tests are conducted in vitro to allow for analysis and comparison of the mechanical performance of intervertebral body fusion device assemblies to specific force modalities.   The forces applied to the intervertebral body fusion assemblies may differ from the complex loading seen in vivo, and therefore, the results from these tests may not directly predict in vivo performance. The results, however, can be used to compare mechanical performance of different intervertebral body fusion device assemblies.  Since the environment may affect the dynamic performance of intervertebral body fusion device assemblies, dynamic testing in a saline environment may be considered.  Fatigue tests should first be conducted in air (at ambient temperature) for comparison purposes since the environmental effects could be significant.  If a simulated in vivo environment is desired, the investigator should consider testing in a saline environmental bath at 37°C (for example, 0.9-g NaCl per 100-mL water) at a rate of 1 Hz or less.  A simulated body fluid, a saline drip or mist, distilled water, or other type of lubrication at 37°C could also be used with adequate justification.

There are three static test methods and two fatigue test methods.  The static test methods are: Compression,  Shear and Torsion.  The fatigue test methods are Dynamic Compression and Dynamic Torsion.

For Static Displacement Tests – The Offset Line location is 2% of the Intradiscal Height.

For Example:

3.5 mm Intradiscal Height * 2%

= 3.5 mm

For a Static Torsion Test – 10 % of the intradiscal height (H) divided by the outside diameter or height of the implant (maximum dimension of implant in XZ plane if not cylindrical) multiplied by 180° divided by PI (π).

For Example:

(14.67 mm intradiscal height * 10%) / 18 mm intervertebral body fusion device assembly * 180° / π

= (14.67 mm * .1) /18 mm * 180° / π

= 4.67°

Example of test results are shown below.

ASTM F2077 Graph 1

ASTM F2077 Graph 2

ASTM F2077 Graph 3

Photos of Test