A phosphocalcic compound modified by a gem-bisphosphonic acid or one of its salts, a method for preparing same, as well as its use for preparing an injectable composition. The modified phosphocalcic compound is obtained by adding a gem-bisphosphonic acid or one of its alkali metal or alkaline earth salts to a suspension of a precursor phosphocalcic compound in ultras-pure water, while stirring the reaction medium at room temperature, then in recovering by centrifuging the formed compound. The compound is useful for making an injectable composition, for use in the treatment of bone remodeling equilibrium.