Apparatus and method for polymerizing cement under pressurized conditions and for applying the cement under pressure at the appropriate time to a human bone cavity for implantation of a prosthesis, including a stemmed femoral component and an acetabular component. This apparatus alters the physical conditions under which bone cement cures, causing a decrease in cement porosity and thus increasing the resultant cement strength. The apparatus includes a pneumatically actuated gun having a piston for applying pressure to the cement, and applying cement to the bone, a pressurizable housing securable to the gun for containing the cement, and a nozzle having a valve which allows the cement to remain pressurized until application thereof through the nozzle. In one embodiment, one component of a two component polymerizable cement is provided in a sealed bladder secured to the nozzle while the other component is injected into the bladder and mixed with the first component when the cement is ready for use. A vent may be provided in the piston of the pneumatic gun to allow air to escape through the piston to prevent the injection of air into the cement. A sealing gasket may be provided on the end of the nozzle for placement over the open end of the bone cavity so that cement can be applied thereto under pressure.