A fluid cement for medical use for bone reconstruction, in particular for filling the vertebral body, and a binary composition which is intended for the preparation of such a cement. A device for conditioning the binary composition, and a method of preparing a bone cement from a binary composition. The fluid cement according to the invention comprises: a) approximately 70% to 85% by weight of a polymer comprising a polymethylmethacrylate and a methylmethacrylate monomer and b) approximately from 15 to 30% by weight of a radio-opaque composition. Preferably, the radio-opaque composition comprises a radio-opacifier, such as barium sulphate and zirconium dioxide, in a mixture with a calcium phosphate, for example apatite hydroxide.