Rapid changes of light microscopic indices of osteoclast-bone relationships correlated with electron microscopy

The relationships of tibial endosteal osteoclasts to bone surfaces were quantitatively evaluated during initiation of calcium repletion in calcium-deficient rats. To do this, indices of osteoclast-bone relationships obtained by light microscopy were devised and evaluated by comparing with those obtained by electron microscopy (EM). These indices are the percent of the osteoclast width that (1) exhibits markers indicative of a ruffled border, (2) is in close contact with bone, (3) is isolated from bone by other cell types, and (4) is separated from bone by intercellular material. The indices obtained by light microscopy were strongly correlated with similar indices obtained by EM and were equally sensitive but considerably easier to obtain. The ruffled border and contact index were significantly decreased by 3 hours after beginning the meal whereas cells of other types became interposed between the osteoclasts and the bone.