Porosity of bone cement reduced by mixing and collecting under vacuum.

Palacos R bone cement was mixed in a commercial vacuum mixing system (MITAB), and in an experimental system allowing evacuating air from the powder before mixing and collecting the cement under partial vacuum. The effect on the porosity of mixing at different pressure levels was tested. The effect of evacuating air from the powder before mixing was also analyzed. The numbers and sizes of the voids in the cement samples were measured in radiographs and under the microscope. Also, the density of the cement was measured. Vacuum mixed samples had a substantial reduction of voids, as well as an increase in density compared to mixing at atmospheric pressure. After vacuum mixing and collection, a further reduction of the porosity and increased density were seen; all the large voids within the cement were eliminated at 0.05 bar absolute pressure.