The standard “ASTM F2009-20 Standard test method for determining axial removal force of tapered connections of modular prostheses” developed by the American Society for Testing and Materials (ASTM) describes a standard methodology for determining the force required under laboratory conditions to remove the tapers of implants that are not otherwise intended to be released. Some examples are total or partial hip replacements or femoral components of the shoulder in which the head and base components are secured together by a self-locking taper.
This test method was developed primarily for evaluating metal and ceramic head designs on metal tapers, but can be applied to other materials and designs.
The axial disassembly test method provides a means to measure the axial locking strength of the tapered connection for modular prostheses. After assembly, an axial tensile force is applied to disassemble the tapered connection and the maximum force is recorded.
This test method helps evaluate the axial locking force of a modular taper. Some types of devices that may use this type of connection are modular shoulder and modular hip prostheses. Additional means of evaluating the locking mechanisms of tapers may be appropriate depending on the design of the device.
This test method may not be suitable for all implant applications. The user is cautioned to consider the suitability of the application in terms of the materials and design tested and their potential applications.
While this test method can be used to measure the force required to separate tapers, any comparison of such data for various component designs must take into account the size of the implant and the type of locking mechanism being evaluated.
During testing, the cone portion of the assembly shall be restrained by suitable fasteners capable of carrying high loads. The fasteners shall be constructed so that the line of load application is aligned within 61 degrees of the axes of the male and female conical components. For example, modular heads may be mounted with a solid metal 100 degree cone as shown in the figure provided in the standard. The cone shall provide line contact around the diameter of the head. For example, modular heads may be mounted with a metal cage surrounding the head and providing uniform contact around the bottom edge of the head as shown in the figure provided in the standard. One method of minimizing alignment error and off-axis loading during constant-rate assembly is to add a thrust bearing to self-center the taper with the mounting cone.
The testing machine shall comply with the requirements of “ASTM E4-13 Standard Practices for Strength Verification of Testing Machines.” The loads used to determine joint strength shall be within the range of the testing machine as defined in this standard.
The testing machine shall be capable of providing compressive and tensile forces at a constant displacement rate or a constant force rate. The testing machine shall be equipped with a load monitoring and recording system.
In terms of sampling and test specimens, the male and female conical components can be completed implants or simplified test specimens. Test specimens should have tapers manufactured to the specifications of a completed implant, including material, and preferably be manufactured with the same equipment. The supporting material around the female taper should be the same size and shape as the completed implant.
A minimum of five tapered assemblies shall be tested to determine the axial pull-out force between tapered components. The pairing of components shall be random unless otherwise specified. The feasibility of performing multiple tests on the same tapered joint depends on the instrument design and application.
Sterilization of test components is not necessary unless there are known effects on the parts being evaluated. Sterilization generally has no effect on metallic materials.
Following normal laboratory cleaning procedures to remove any debris or other surface contaminants, the conical components are assembled on a suitable testing machine. A recommended procedure for cleaning and drying the samples is included in the standard appendix (Annex X1).
Among the numerous testing, measurement, analysis and evaluation studies that our organization has carried out for businesses in various sectors, our organization also provides testing services defined in the standard “ASTM F2009-20 Standard test method for determining the axial removal force of conical connections of modular prostheses” with its trained and expert staff and advanced technological equipment.
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