The present invention relates in certain embodiments to medical devices for treating osteoplasty procedures such as vertebral compression fractures. More particularly, embodiments of the invention relate to instruments and methods for controllably restoring vertebral body height by controlling the geometry of bone cement introduced into the interior of a vertebra. An exemplary system utilizes Rf energy in combination a conductive bone cement for polymerizing the inflow plume to control the geometry of the fill material and the application of force caused by inflows of cement. In another embodiment, a method of treating bone includes utilizing a controller to control (i) bone cement inflow parameters and (ii) energy delivery parameters selectively modify the viscosity of a selected portion of bone cement as it is introduced. A system for treating bone includes an introducer for delivering bone and an energy source selectively coupleable to the bone cement to alter the viscosity of the fill material as it flows out of the introducer. One method includes pulsing the inflows of bone cement and further applying pulsed aspiration forces to the interior of the vertebra to relieve interior pressures to prevent emboli from migrating into the venous system.