Abstract
Fatigue failure of the acrylic cement mantle is one of the most common causes of aseptic loosening in cemented femoral prostheses. Cement fatigue properties can be assessed by mechanical in vitro tests, usually performed on properly shaped specimens from standard molds, following a controlled procedure. On the contrary, in the operating theatre the cement mantle is produced in the medullary channel after stem insertion by the surgeon. It is arguable whether the cement properties obtained from the in vitro tests reflect the actual fatigue properties of the cement mantle, as a less controlled procedure can create more defects in the cement. To evaluate the influence of cement preparation, molded specimens for fatigue tests were produced by three different methods. Specimens were molded, using hand-mixed cement, into a standard mold or into a purposely designed device, simulating stem insertion in the medullary channel. Two different specimens were molded with this device, the cement manually or syringe inserted. Fatigue tests were carried out with a sinusoidal uniaxial zero-tension load (15 MPa) and cycle numbers at failure recorded for the three different groups of specimens.
The results showed that, in the case of specimens properly manufactured (using a syringe) the fatigue strength reaches values similar to those of standard molded specimens, but it significantly decreases if cement is not inserted according to proper surgical procedures. Therefore, in the operating theatre it is recommended that the correct and complete procedure is followed to limit the risk of early fatigue failure of the mantle.