1. Scope1.1 This test method covers

1. Scope
1.1 This test method covers a standard methodology by which to measure the attachment strength between the modular acetabular shell and liner. Although the methodology described does not replicate physiological loading conditions, it has been described as a means of comparing the integrity of various locking mechanisms.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appro¬priate safety and health practices and determine the applica¬bility of regulatory limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
E4 Practices for Force Verification of Testing Machines
F2345 Test Methods for Determination of Static and Cyclic Fatigue Strength of Ceramic Modular Femoral Heads
3. Terminology
3.1 Definitions of Terms Specific to This Standard:
3.1.1 acetabular liner—portion of the modular acetabular device with an internal hemispherical socket intended to articulate with the head of a femoral prosthesis. The external geometry of this component interfaces with the acetabular shell through a locking mechanism which may be integral to the design of the liner and shell or may rely upon additional components (for example, metal ring, screws, and so forth).
3.1.2 acetabular shell—the external, hollow (usually metal) structure that provides additional mechanical support or rein-forcement for an acetabular liner and whose external features interface directly with the bones of the pelvic socket (for example, through bone cement, intimate press-fit, porous ingrowth, integral screw threads, anchoring screws, pegs, and so forth). The acetabular shell may be either solid or contain holes for fixation, or contain a hole for instrumentation, or all of these.
3.1.3 locking mechanism—any structure, design feature or combination thereof, that provides mechanical resistance to movement between the liner and shell.
3.1.4 polar axis—the axis of revolution of the rotationally symmetric portions of the acetabular liner or shell.
4. Summary of Test Method
4.1 All acetabular liners shall be inserted into the acetabular shells for testing by applying a force of 2 kN. This value is similar to the force required to set the head in Test Methods F2345.
4.2 Axial Disassembly:
4.2.1 The axial disassembly of an acetabular device test method provides a means to measure the axial locking strength of the acetabular liner for modular acetabular devices.
4.2.2 Following proper assembly of the acetabular liner in an acetabular shell, the assembled device is attached to a fixture such that the cup opening is facing downward. The acetabular shell is supported and an axial force is applied to the acetabular liner until it disengages. The force required to disengage the acetabular liner from the acetabular shell is recorded.
4.3 Offset Pullout or Lever Out Disassembly:
4.3.1 The offset pullout or the lever out disassembly method is intended to assess the resistance of the locking mechanism to edge forces that could occur when the neck of a hip prosthesis impinges on the edge of the acetabular liner. An impinging force could cause the edge of the acetabular liner opposite the area of impinging contact to be pushed out of the shell. The resistance of the acetabular liner edge to being pulled loose from the shell is a measure of the resistance to impingement causing loosening of the acetabular liner
4.3.2 Following proper assembly of the acetabular liner in an acetabular shell, the assembled device is attached to a fixture such that the cup opening is facing upward. The acetabular shell is constrained from moving at a minimum of four locations spaced uniformly around the top circumference of the acetabular shell. For an offset pullout a force is applied to a liner contact point, a location near the top surface of the liner. The line of action of the force is constrained to a direction that is parallel to polar axis of the liner. The force required to disengage the acetabular liner from the acetabular shell is recorded.
4.3.3 For a lever out test, the force is applied through a lever mechanism with a liner contact point near the top surface of the liner and a fulcrum that is outside the liner and directly opposite the contact point. The centerline of the lever shall intersect the polar axis of the liner. The force required to disengage the acetabular liner from the acetabular shell shall be recorded. The distances between the applied force and the fulcrum and the resultant force and the fulcrum are recorded. These values are used to calculate the lever-out force.
4.4 Torque Out Disassembly:
4.4.1 The torque out disassembly method is intended to assess the resistance of the locking mechanism to high friction events that would attempt to rotate the acetabular liner within the acetabular shell.
4.4.2 Following proper assembly of the acetabular liner in an acetabular shell, the assembled device is attached to a fixture such that the shell opening is unimpeded, allowing the acetabular liner to be pushed free of the shell. The acetabular shell is constrained from moving at a minimum of four locations spaced uniformly around the top circumference of the acetabular shell. A head of a diameter appropriate to the liner is attached to the liner at a minimum of four equally spaced locations or adhesively bonded. A torque is applied through the head along the polar axis of the liner. The torque required to disengage the acetabular liner from the acetabular shell or break the adhesive bond between the articulating surfaces of the acetabular liner and the head is recorded.
5. Significance and Use
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 appropriate¬ness 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, com¬parison 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
5.4 Material failure is possible before locking mechanism failure during either push-out or offset pullout/lever-out con¬ditions. 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.
*
6. Apparatus
6.1 An apparatus capable of supporting only the acetabular shell while allowing the acetabular liner to be freely disas¬sembled from the shell is required.
6.2 The testing machine shall conform to the requirements of Practices E4. The loads used to determine the attachment strength shall be within the range of the testing machine as defined in Practices E4.
6.3 The test machine shall be capable of delivering a compressive or tensile force at a constant displacement rate. The test machine shall have a load monitoring and recording system.
7. Sampling
7.1 All acetabular liners shall be representative of implant quality products. This shall include any sterilization or thermal processes which may alter the material properties or geometry.
7.2 A partially finished acetabular shell or permanent fixture block may be substituted for a completed acetabular shell provided that the internal materials, finish, locking mechanism, and geometry are identical to the actual acetabular shell.
7.3 A minimum of five shell and liner assemblies shall be tested in each of the three tests (axial, offset pullout or lever-out, and torque-out disassembly) to determine the disas¬sembly values. Pairing of the acetabular shells and liners shall be at random unless otherwise reported. For tests with poly¬ethylene liners, the same five acetabular shells may be used for each of the three tests provided that none of the shells are damaged by any of the preceding tests.
8. Procedure
8.1 Assembly Procedure:
8.1.1 The liner shall be assembled in the shell with a peak force of 2 kN ± 50 N. The force shall be applied in displacement control at a rate of 0.04 nim/s or force control at a rate of 1 kN/s or less. The line of force application shall be coincident with the polar axis of the liner. The force may be 
8.2.1 Once assembled, the liner shell construct shall be placed in a solid metallic fixture with continuous support of the shell as illustrated in Fig. 1. The fixture that supports the acetabular shell shall do so without visual evidence of defor¬mation during or after the test. An axial force shall be applied (coincident with the polar axes of the liner and shell) to the liner through a center hole (polar axis of the acetabular shell) in the shell at a rate of 5.1 cm/min with a round rod. The direction of force application and rod longitudinal axis shall be collinear to the polar axes of the liner and shell to within 2°; and the center of the rod contact with the liner shall be less than 2 mm from t