The present invention relates in certain embodiments to medical devices for treating vertebral compression fractures. More particularly, embodiments of the invention relate to instruments and methods for controllably restoring vertebral body height by controlling the flow of bone cement into the interior of a vertebra and the application of forces causes by the cement flow. An exemplary system utilizes Rf energy in combination a conductive bone cement for selectively polymerizing the inflow plume to increase the viscosity of the cement. In one aspect of the invention, the system utilizes a controller to control bone cement flow parameters to either allow or disallow cement interdigitation into cancellous bone. A method of the invention includes pulsing the flows of bone cement wherein high acceleration of the flow pulses can apply expansion forces across the surface of the cement plume to reduce a vertebral fracture.