A bovine bone block was pulverized by an automatic high-speed blade mill together with ice blocks made of normal saline. The bone granules obtained were classified with standard sieves of 500, 710, 1000 and 2000 mu m in mesh size. Micrographs taken under an optical microscope were binarized to measure the major and minor axes of each granule with image analysis software. To obtain the particle size distribution by combining the results from sieving and image analysis, a new approach was proposed. When the Heywood diameter was used as a characteristic diameter, the existence of granules larger than the mesh size was recognized. This result can be attributed to the prolonged shape of the bone granules as explained by using the Feret diameter. A tendency that a larger aspect ratio was observed for smaller granules was found. This result can also be explained to be due to the anisotropy in shape, attributed to the intrinsic property of bone. (C) 2014 Elsevier B.V. All rights reserved.