ASTM F1612-95 Standard Practice for Cyclic Fatigue Testing of Torsion Metal-Stem Hip Arthroplasty Femoral Components

The ASTM F1612-95 standard, "Standard Practice for Cyclic Fatigue Testing of Torsional Metal-Stemmed Femoral Components in Hip Arthroplasty," developed by the American Society for Testing and Materials (ASTM) , describes a method for fatigue testing of metallic-stemmed femoral components used in hip arthroplasty. This method is designed for evaluation purposes in comparing various designs and materials used for stemmed femoral components in arthroplasty. The practice encompasses procedures for performing fatigue tests using a periodic, constant amplitude force (as the forcing function).

This standard applies primarily to modular head-mounted, one-piece prostheses with a head in place and femoral stems. Such prostheses should have no anteroposterior AP arch or medial-lateral ML arch and should have a nearly straight section in the distal 50 mm of the stem. This practice may require modifications to accommodate other femoral stem designs.

For the purposes of this standard, the following terms and definitions apply:

The cantilever plane refers to a plane perpendicular to the load application line at the level where the body becomes unsupported.
The distal body axis is the centerline of the most distal 50 mm of the body in AP projection and ML projection.
Estimated maximum bending moment, is the maximum compressive load times the no-load moment arm.
The geometric center of gravity (cantilever plane) is the point in the cross-sectional area of the cantilever plane whose coordinates are the average values of the coordinates of all points in the area.
The load application line is the loading axis of the testing machine.
The R value represents the ratio of minimum force to maximum force.
The reference line L1, the distal root axis, is the ML centerline of the most distal 50 mm of the root in the AP projection.
Reference line L2, collar device, is the plane of the distal side of the collar in AP projection
Reference line L2, collarless device, is the recommended resection plane for the device in AP projection
The reference point P1 is the spherical center of the prosthetic head.
The reference point P3, the collar device, is the point where the major axis of the collar (L2) intersects the medial surface of the root in the AP projection.

This application can be used to characterize the effects of materials, manufacturing, and design variables on the fatigue resistance of femoral components with metallic stems subjected to cyclic loading for a relatively large number of cycles. The proposed test assumes a worst-case situation where proximal support for the stem is lost. It is also recognized that for some materials the medium has an effect on the response to cyclic loading. The test medium used and the rationale for its selection should be described in the test report.

It is assumed that actual in vivo loading conditions are not constant amplitude. However, there is insufficient information available to establish standard load spectra for femoral components with metallic stems. Accordingly, a simple periodic constant amplitude force is recommended.

Fatigue data on femoral stems must be reproducible across laboratories to be useful for comparison. Consequently, it is essential to establish uniform procedures for testing and reporting test data.

The specimen should be confined within a rigid cavity with a suitable grout. A common grout used is polymethyl methacrylate (bone cement). The minimum thickness of the grout should be 1 cm. Although bone cement is the recommended grout, other materials may be used provided that they do not chemically or mechanically alter the test specimen. Test fixtures should be constructed so that the load application line is in the implant AP plane of symmetry of the supported portion of the stem. Test fixtures should be constructed so that the load application line passes through the ball center. A low-friction mechanism with ball or roller bearings should be incorporated into the loading apparatus to minimize loads that are not perpendicular to the cantilever plane. An example of such a mechanism is included in the standard appendix (Annex X2).

Among the numerous testing, measurement, analysis and evaluation studies that our organization has provided for businesses in various sectors, our organization also provides testing services defined in the standard “ASTM F1612-95 Standard practice for cyclic fatigue testing of torsion metal stem hip arthroplasty femoral components” with its trained and expert staff and advanced technological equipment.