The mechanical behaviour of a pre-formed hip spacer

Abstract

This study investigated the mechanical behaviour under dynamic load of a preformed hip spacer made of antibiotic impregnated bone cement (Spacer G 60, Tecres SpA, Sommacampagna VR, Italy) used in two-stage treatment of infected hip prostheses. In the experimental protocol the spacer was assumed as a temporary hip hemiarthroplasty so was liable to the same level of load stresses. Therefore, the cycling loading procedure was defined following the recommendation of the ISO 7206/4:1989 standard for determination of fatigue performance of hip stems. Three spacers were subjected to a 4 Hz cyclic load ranging between 300 and 2300 N until specimen failure or for 0.5 million cycles. This loading condition was chosen to simulate six months of patient use without any restriction in moving or loading the operated hip, which should represent the worst load history conditions for the device. One out of the three spacers completed the test. The remaining two spacers failed at 0.40 and 0.45 million cycles. These results demonstrated that the investigated spacer has finite fatigue strength when subjected to the described loading conditions but failure occurs only at the end of a very extreme loading history, hardly ever reproduced in standard clinical practice. Since decreasing the load level increases the fatigue life, the surgeons can safely implant the spacer if the patient is allowed partial weightbearing, as it is in standard clinical practice.