Packaging is tested under compression according to ASTM D642 in order to simulate transportation or storage conditions. The packaging sample is placed between two horizontal plates and subjected to static loading. The test is terminated when a specified deformation is reached or when a drop in reaction force occurs. The maximum applied test force and the corresponding deformation of the packaging are recorded.
In March 2022, ASTM published the standard for fatigue testing of the femoral component of knee replacements. This standard complements the fatigue testing of tibial plateaus according to ISO 14879-1 and is the first published standard specifically addressing the fatigue strength of the femoral component.
The test is conducted under “closing conditions,” meaning the femoral component is cyclically compressed along its anterior-posterior axis. Only one posterior condyle is loaded, while the anterior flange is fixed.
A total of 10 million cycles is recommended.
This fatigue test is applied to bicondylar knee replacements and specifically targets the metallic tibial plateau (tibial tray). For the test, the plateau is embedded on one side (medial or lateral), while the other side is free to flex. The fatigue strength of the tibial plateau is evaluated under specified cyclic loads and numbers of cycles.
This fatigue test is not applied to cemented tibial components made solely of polyethylene (all-poly) that do not have a metallic plateau.
ISO 5833 specifies, among other things, compression and bending tests for bone cement specimens. We offer static compressive strength testing and static bending strength testing as testing services. For bending strength determination, a four-point bending test is performed. If required, bone cement specimens can be manufactured in our laboratory using our own standard-compliant casting molds.
Testing of dough time is also included within our accredited scope.
We are also pleased to perform additional tests on bone cement products, such as fatigue tests on cement spacers. Please feel free to contact us!
The ball pull-off test, like ISO 7206-13, assesses the strength of the taper connection between the hip stem and ball head according to the specified assembly technique. Instead of measuring the torque required to loosen the connection, ASTM F2009 measures the axial pull-off forces.
This is also a static test involving a single application of load.
The corrosion testing of the taper connection according to ASTM F1875 can be performed using two different methods:
Method 1:
The taper connection of the hip replacement is subjected to at least 10 million load cycles in a test chamber filled with electrolyte (0.9% NaCl) following ASTM F1140. The isolated fluid is chemically analyzed for particles and ions. Afterwards, the components of the taper connection are examined microscopically and with an electron microscope. Additionally, weight loss can be measured as an indicator of wear. This method quantitatively measures particles and ions and qualitatively assesses surface damage of the taper due to micromotion and corrosion.
Method 2:
The hip replacement is placed in a test chamber filled with electrolyte solution (0.9% NaCl), so that the electrolyte covers the taper and part of the stem. The contact surfaces are isolated from the electrolyte. The taper connection is loaded as in Method 1 according to ASTM F1140, but forces and test frequency may be lower.
This test evaluates the fixation of inserts in the acetabular shell to compare the effectiveness of different insert fixation mechanisms. It includes three different tests. The shell is fixed in all tests using a suitable fixture to prevent movement of the shell while allowing the insert to be released. Before each test, the insert is fixed in the shell with a force of 2000 N (ASTM F2345).
Axial push-out test
A displacement is applied to the insert along the polar axis through a hole in the pole of the acetabular shell until the insert detaches from the shell. The resulting force is measured.
Offset pull-out test or lever-out test
For this test, a slot or hole is first created inside the insert at approximately 80% of its depth. Then, an axial displacement parallel to the polar axis is applied to the insert via a rod (offset pull-out test). Alternatively, the insert can be levered out using a lever arm that engages the slot or hole (lever-out test).
Torsion test
For this test, grooves parallel to the polar axis are introduced into the insert, into which springs on a prepared ball head engage. Alternatively, a ball head can be glued into the insert. Then, torsion is applied around the polar axis via the ball head until the insert is released.
The procedure specified in ISO 21535 measures the range of motion (ROM) of hip replacements. This can be performed either on the actual component or within a CAD environment. The ranges of motion up to impingement are measured in the directions of flexion/extension, adduction/abduction, and internal/external rotation.
The standard defines minimum rotation angles that the product must be able to achieve before impingement occurs.
The ball torsion test provides information about the torque required to loosen the taper connection between the hip stem and the ball head after the specified assembly technique. This is a static test involving a single application of load.
The static burst test evaluates the strength of the ball head in connection with the stem taper. After assembling the head onto the stem taper with a defined force, a static axial load is applied to the ball head at a specified rate. One of the failure criteria is fracture of the head. For a successful test, five samples must withstand the defined maximum load without failure.
