Ten Years of Experience with test Criteria for Fracture-Proof Anchorage Stems of Artificial Hip Joints

Abstract

Since loosened femoral component stems are subjected to severe stresses, the material of which the stem is made becomes over-stressed and this may eventually result in an absolutely undesirable fatigue fracture of the loosened stem. Extensive static stress measurements performed along the lateral aspect of simulated loosened stems of various hip prosthesis types yield load/stress curves for determining the safety factor for the structural strength of the stem design. Decisive for the safety against fracture of a loosened femoral prosthesis stem is, ultimately, the dynamic pulsating fatigue test at up to 5 × 10⁶ load cycles in Ringer's solution. Under the given test conditions as many as 2000 hip prosthesis stems have been subjected to 5–10 million load cycles over the last ten years, and minimum requirements have been laid down for the fracture-safety of these components under conditions of loosening in the body. The experience gained over a period of ten years with more than 500 000 series-produced fracture-proof anchorage stems strongly suggest that these test conditions should be standardized nationally and internationally.