Abstract: A bone graft substitute which combines substantially the high mechanical stability of spherical porous granules without the limitation of reduced intergranular space. The granules have a high porosity whilst maintaining high stability, and can be pushed into a defect without risking significant breakage of the granules and, simultaneously, bone cells can grow into the space between the granules. In an exemplary embodiment of the invention, the surface of the granules comprises indentations, when viewed from the exterior of the granules. An indentation increases the porosity within the implanted mass significantly and thus provides more space between the granules for tissue ingrowth. Due to the indentations on the granules, the granules have an irregular shape and thus an increase in the intergranular space is achieved, while mechanical stability is maintained. A biocompatible polymer, such as a collagen or gelatin, is disposed about at least some of the granules to form a coating thereon.