ASTM F2028 – Standard Test Methods for Dynamic Evaluation of Glenoid Loosening or Disassociation
These test methods measure how much a prosthetic anatomic glenoid component rocks or pivots following cyclic displacement of the humeral head to opposing glenoid rims (for example, superior-inferior or anterior-posterior). Motion is quantified by the tensile displacement opposite each loaded rim after dynamic rocking. Similarly, these test methods measure how much a prosthetic reverse glenoid component rocks or pivots following cyclic articulation with a mating humeral liner. Motion is quantified by the magnitude of displacement measured before and after cyclic loading. The same setup can be used to test the locking mechanisms of modular glenoid components, for example, disassociation of both anatomic and reverse shoulder components. These test methods cover shoulder replacement designs with monolithic or modular glenoid components for cemented fixation as well as reverse glenoid components for un-cemented fixation.
This test method is intended to investigate the resistance of a glenoid component to loosening. Glenoid loosening is the most common clinical complication in total shoulder arthroplasty. The method assumes that loosening occurs because of edge loading, often called the rocking-horse phenomenon. This test method can be used both to detect potential problems and to compare design features. Factors affecting loosening performance include articular geometry, flange geometry, materials, fixation design, bone quality, and surgical technique.
Prosthetic Anatomic Glenoid Component
Testing consists of performing a Subluxation test in both the Superior-Interior directions for a symmetrical Glenoid. For a non-symmetrical Glenoid, a Subluxation test is performed in the Superior- Interior and Anterior-Posterior directions. Generally, 2 to 3 Glenoids are tested for the Subluxation test. Average the displacements that were recorded at the maximum shear load for each direction. Calculate 90% of for each average.
- Symmetrical Glenoid uses 90% of the largest average for the cyclic horizontal displacements.
- Non-Symmetrical Glenoid uses 90% of the largest average from each direction as the cyclic horizontal displacements. A cyclic test is performed in the Superior- Interior and Anterior-Posterior directions, 3 tests per direction.
Edge Displacement measurements are performed on the cyclic sample before and after the cyclic test.
An axial load for 750 Ns is applied to the sample and is maintained throughout the cyclic test. The cyclic test is performed in horizontal displacement control at < 6 Hertz for 100,000 cycles. A minimum number of 3 samples are cycled tested.
Prosthetic Reverse Glenoid Component (reverse shoulder)
Edge Displacement measurements (3 sets) are performed on the cyclic sample before and after the 10,000 cycle rotational tests.
An axial load for 750 Ns is applied to the sample and is maintained throughout the cyclic rotational test. Rotate the sample 45° (+/- 22.5°) for 10,000 cycles at 0.2 Hertz.