A system for injection of bone cement material into a bone, the system comprising: (a) a quantity of a bone cement material formed from a first powder component which contains pre-polymerised beads having a first average molecular weight and including a high molecular weight population of beads having a second average molecular weight that is higher than the first average molecular weight, and a second liquid component which contains a monomer, the pre-polymerised beads having selected sizes and selected molecular weights such that when the polymer and the monomer components are mixed, the mixture has a viscosity of at least 500 Pa.s within a period of 120 seconds after mixing, the viscosity changing by less than 200 Pa.s during a period of at least two minutes after the viscosity of the mixed cement reaches 500 Pa.s, (b) a reservoir for containing the bone cement material prior to injection into a subject's bone, the reservoir being deployed external to a body of the subject, (c) a cannula which is adapted for insertion into the bone and which can be connected to the reservoir for delivery of bone cement material from the reservoir to the bone, (d) a pressure source adapted to apply sufficient pressure to bone cement material in the reservoir to expel at least a portion of the material from the reservoir through the cannula, the pressure source including an electric actuator for activating the pressure source, in which the actuator can be operated to deliver the bone cement to the subject's bone during the period of at least two minutes in which the viscosity of the bone cement material is 500 ± 200 Pa.s, and in which the viscosity of the mixture is measured using a capillary extrusion rheometer for measuring an applied force acting on a piston to displace the mixture in a capillary tube at a constant displacement rate, the measurements being performed at an average temperature of 22.3 °C and a constant displacement rate of 3 mm.min -1. (a) a quantity of a bone cement material formed from a first powder component which contains pre-polymerised beads having a first average molecular weight and including a high molecular weight population of beads having a second average molecular weight that is higher than the first average molecular weight, and a second liquid component which contains a monomer, the pre-polymerised beads having selected sizes and selected molecular weights such that when the polymer and the monomer components are mixed, the mixture has a viscosity of at least 500 Pa.s within a period of 120 seconds after mixing, the viscosity changing by less than 200 Pa.s during a period of at least two minutes after the viscosity of the mixed cement reaches 500 Pa.s, (b) a reservoir for containing the bone cement material prior to injection into a subject's bone, the reservoir being deployed external to a body of the subject, (c) a cannula which is adapted for insertion into the bone and which can be connected to the reservoir for delivery of bone cement material from the reservoir to the bone, (d) a pressure source adapted to apply sufficient pressure to bone cement material in the reservoir to expel at least a portion of the material from the reservoir through the cannula, the pressure source including an electric actuator for activating the pressure source, in which the actuator can be operated to deliver the bone cement to the subject's bone during the period of at least two minutes in which the viscosity of the bone cement material is 500 ± 200 Pa.s, and in which the viscosity of the mixture is measured using a capillary extrusion rheometer for measuring an applied force acting on a piston to displace the mixture in a capillary tube at a constant displacement rate, the measurements being performed at an average temperature of 22.3 °C and a constant displacement rate of 3 mm.min -1.