The American Society for Testing and Materials (ASTM) standard, “ASTM F2724-21 Standard Test Method for Evaluating Dislocation of a Mobile Bearing Knee,” describes a test method for determining the dislocation resistance of mobile bearing knee designs with respect to femoral component separation and rotation of the mobile bearing insert. Although the described methodology does not reflect all physiological loading conditions, it is a means of in vitro comparing mobile bearing knee designs and their ability to resist dislocation of the femoral or tibial components under specified test conditions. This test method applies only to mobile bearing total knee designs.
This test method is designed to provide a standard method for determining the restriction of mobile bearing knee designs with respect to spin-out and spit-out of the mobile bearing. Spin-out refers to excessive rotation of the bearing component in a rotating platform knee or multi-directional platform knee, resulting in dislocation between the femoral or tibial components and the mobile bearing. Spit-out refers to the bearing component moving forward or backward from under the femoral component.
Similar to the restraint testing of total knees (ASTM F1223-20 Standard Test Method for Determining Total Knee Replacement Restraint), it is important to note that the test method does not simulate the soft tissues and laxity of the knee joint, which may be the primary factors involved in the occurrence of spin-out or spit-out. For example, a patient with good soft tissue restraints will likely require a lower spin-out/spit-out resistance, whereas a patient with extensive bone loss or destroyed ligaments will likely require an implant with a higher spin-out/spit-out resistance. Therefore, the test results must be considered in conjunction with the condition of the patient's soft tissues to determine the relative safety of the device.
An engineering analysis should be performed on all dimensions of the knee design to justify the worst case size for this test. A minimum of five mobile bearing inserts should be tested at this size. The tibial tray and knee femoral component can be reused for multiple trials as long as they are not damaged during testing.
The moving bed surfaces should be lightly covered with water (e.g., reverse osmosis water, deionized water, or distilled water) to reduce friction effects during testing.
A two-axis orthogonal load frame with feedback control should be used for dislocation testing. The machine should be capable of recording force and displacement in both axes.
Fixtures are required to allow 80 percent medial and 20 percent lateral load distribution to be applied through the condyles of the femoral component.
During testing, the tibial tray posterior tilt and the degree of femoral component flexion should be adjusted according to the recommended surgical alignment.
All components should be inspected prior to testing to ensure that they meet geometric and material specifications. Tibial inserts should be sterilized as normally used with real implants. Test components should be exposed to a clean atmosphere at 24 plus/minus 25 degrees for 5 hours prior to testing.
Dislocation testing should be performed at 0, 60, and 90 degrees of flexion and at the maximum flexion angle the implant is intended to achieve. If design permits, the testing procedure can address spin-out and spit-out simultaneously.
The tibial tray or femoral component should be able to move freely in the anterior and posterior directions under actuator control. A compressive joint reaction force should be applied to the mobile bearing knee in the superior/inferior direction via the tibial tray or femoral component. The femoral component should be oriented in the desired flexion angles for testing.
Among the numerous testing, measurement, analysis and evaluation studies that our organization has provided for businesses in various sectors, it also provides testing services defined in the "ASTM F2724-21 Standard Test Method for Evaluating Mobile Bed Knee Dislocation" standard with its trained and expert staff and advanced technological equipment.
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