POROSITY OF BONE-CEMENT REDUCED BY MIXING AND COLLECTING UNDER VACUUM

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