ASTM F2724 Mobile Bearing dislocation test
The test described in ASTM F2724 serves to determine the resistance of a knee endoprosthesis system to a "spin-out" or "spit-out" of mobile bearings. The femoral and tibial components are oriented at 0°, 60°, 90° and the maximum flexion angle. Under a constant load of 710 N (with the force applied to 80% over the medial condyle and 20% over the lateral condyle) one of the two components is displaced (anterior or posterior) until one of the femoral condyles loses contact with the mobile bearing. The maximum load is determined, when one of the condyles lose contact to the mobile bearing. Afterwards, it is evaluated whether a "spin-out" or "spit-out" occurs first.
A "spin-out" describes a very pronounced twisting of the knee components as a consequence of which a release of the femur or tibial component from the mobile bearing occurs.
A "spit-out" describes an anterior or posterior sliding out of a mobile bearing below the femoral component.