Static and fatigue properties of two new low-viscosity PMMA bone cements improved by vacuum mixing.

With the objectives of reducing toxicity and improving the mechanical properties of the prior Sulfix-6 cement, a new low-viscosity bone cement with a new catalyst (Sulfix-60), and a gentamycin containing cement (Allofix-G) were developed. Although static strength could be improved in comparison with the older Sulfix-6 cement, investigations regarding improved fatigue strength and the influence of vacuum mixing on the mechanical properties were missing. Dynamic weakness was the major disadvantage of the older Sulfix-6 cement. To investigate fatigue strength specimens of the new bone cements were tested with load guiding until breakage or 20 million cycles. In the three series, hand mixing, vacuum mixing, and vacuum mixing with additional pressurization were performed, respectively. Vacuum mixing led to increased fatigue stability from 6.3 to 9.1 MPa for Sulfix-60, and from 6.3 to 8.2 MPa for Allofix-G. Additional compression had no significant effect. A 200% increased fatigue strength was detectable in comparison with the older cement. In the four-point bending test, similar results were found. It could be proved that an increased polymerization rate achieved with the use of the new catalyst was responsible for the improved mechanical properties of the new bone cement Sulfix-60.