Bimodal distribution of osteocyte lacunar size in the human femoral cortex as revealed by micro-CT

Tomographic reconstructions of sections of human femoral bone were created from x-ray data sets taken using synchrotron radiation of 26.4 keV and with isotropic voxels 1.47 μm on a side. We demonstrate that it is possible to segment the data to isolate both the osteocyte lacunae and the Haversian canals in the bone as well as identifying osteon boundaries. From this information a wealth of data relating to bone structure becomes available. The data were used to map the spatial positions of the osteocyte lacunae, relative to the Haversian canals and of the osteon boundaries. The dimensions and volume of the imaged osteocyte lacunae were measured for close to 10,000 lacunae. When averaged over the 11 osteons measured, osteocyte densities varied from 4 × 104 per mm3 close to the Haversian canals to about 9 × 104 per mm3 at 80% of osteon radius. The nearest-neighbour distances varied from 10 μm to 40 μm with a peak at 23 μm and an approximately normal distribution. The distribution of lacunar long-axis length was also approximately normal with a small positive skew and the peak value was 8 μm with a range from 3 μm to 20 μm. The most significant finding from this study was that the distribution of the measured volumes of osteocyte lacunae had two distinct peaks, one at 200 μm3 and a second at 330 μm3.