5.1 This test method is intended to help assess the locking strength of the acetabular liner in a modular shell when subjected to three different force application conditions.

5.2 This test method may not be appropriate for all implant applications. The user is cautioned to consider the appropriateness of the method in view of the materials and design being tested and their potential application.

5.3 While these test methods may be used to measure the force required to disengage modular acetabular devices, comparison of such data for various device designs must take into consideration the size of the implant and the type of locking mechanism evaluated. The location of the locking mechanism relative to the load application may be dependent upon the size and design of the acetabular device. In addition, the locking mechanism itself may vary with size, particularly if the design is circumferential in nature (for example, a larger diameter implants would have a greater area of acetabular shell/acetabular liner interface than a small diameter implant).

5.4 Material failure is possible before locking mechanism failure during either push-out or offset pullout/lever-out conditions. This is due to the possibility that the shear strength of the material may be exceeded before the locking mechanism is fully tested. If this occurs, those results shall be reported and steps taken to minimize this effect. Some possibilities for minimizing shear might include utilizing the smallest size components, using a flat rod end rather than a round rod end or placing a small metal plate between the liner and shell (during push-out). For well-designed polyethylene inserts, it may not be possible to push out or offset pullout/lever out the liner without fracture. In some cases, reporting the maximum force and acknowledging that the true disassembly force will be higher may be justified.