Size and density of osteocyte lacunae in different regions of long bones

SummarySize and density of osteocyte lacunae were evaluated at different levels of long bones to investigate whether or not the proportion of bone tissue occupied by osteocytes changes in skeletal regions, characterized by clear-cut differences in bone turnover rates. Statistical analysis of the results shows that the mean cross-sectional area of osteocyte lacunae (C) is lowest in compact bone of diaphysis and metaphysis, highest in spongy bone of metaphysis and epiphysis. On the contrary, the mean surface of bone tissue surrounding each osteocyte (T=bidimensional osteocyte territory, indirectly calculated from the number of lacunae/mm2 of bone) is largest in compact bone of diaphysis, smallest in metaphyseal spongiosa, and shows intermediate values in the cortex of metaphysis and in epiphyseal spongiosa. The proportion of bone tissue occupied by osteocyte lacunae (%C/T) appears to follow at different levels of long bones, the same pattern recorded for the data of bone turnover rate, by the tetracycline labeling technique: it is lowest in mid-diaphyses, highest in metaphyses, and intermediate in epiphyses. On the basis of these findings, it is suggested that the action exerted by osteocytes on the surrounding calcified matrix, whatever the function of these cells, is not uniform throughout the skeleton and is to some extent correlated with the activity of the other bone cells—osteoblasts and osteoclasts.The significance of some of the data reported is also discussed in relation to investigations of periosteocytic lacunar morphometry.