Procedures for the mechanical testing of shoulder replacements
ASTM F1829 describes a test method to determine the static shear force required to loosen modular glenoid components (insert and backing) of shoulder replacements. The test is suitable for metal joints, polymers, or composites and is used for design validation or comparison with other replacements. Wherever possible, the test should reflect the clinical use of the implant, meaning representative specimens of the finished product are tested and sterilized as required by the manufacturer.
For testing, specimens are fixed in the testing machine parallel to the implant axis. A vertical load is first applied from inferior to superior, and the loosening rate is recorded. The test is stopped when one of the following occurs:
- The insert separates from the backing
- The applied load reaches its maximum and begins to decrease
- Gross deformation of the insert occurs without loosening
After this, a new insert is placed in the test fixture, and the test is repeated under the same conditions but applied from anterior to posterior. The test is stopped again as soon as one of the above cases occurs. The backing is visually inspected for damage after each test.
At least five equivalent samples should be tested, and the test can be conducted either in air at room temperature or under defined physiological conditions.
We offer a testing procedure to evaluate the fixation strength of the glenoid component in bone and its resistance to subluxation caused by cyclic movement (e.g., superior-inferior or anterior-posterior) of the humeral head against the edge of the glenoid, according to the ASTM F2028 standard. This test method can be applied to both cemented monolithic and modular glenoid components as well as uncemented reverse glenoid components.
The glenoid component is fixed in a bone substitute material using bone cement, and the humeral head component is placed into the glenoid component. An axial load is applied through the glenoid component while the humeral head is moved in opposite directions to determine the maximum displacement before dislocation. Then, the humeral head is cyclically moved at a speed of up to 50 mm/min for 100,000 cycles in both directions until 90% of the displacement at dislocation is reached. During the test, axial displacement (rocking) of the glenoid edges is recorded. The test can be conducted dry or in water at 37°C.
