Osteocyte lacunar size–lamellar thickness relationships in human secondary osteons

Previous investigations carried out in our laboratory on secondary osteons have shown that osteocyte lacunae decrease in size from the cement line towards the Haversian canal, and lamellar bone is made up of alternating nonosteocytic dense lamellae and osteocytic loose lamellae, all having an interwoven texture of collagen fibers. Such alternation of acellular and cellular lamellae was hypothesized to depend on osteocyte recruitment from osteogenic laminae in successive layers, assuming that the loose lamellae form because of alignment and fusion of the periosteocytic loosely arranged collagen fibers. In order to discover whether a correlation really exists between osteocyte lacunar size and lamellar thickness, as would be expected if the above-mentioned hypothesis were true, both these parameters were measured in completed secondary osteons in relation to their distance from the Haversian canal. The size of osteocyte lacunae was measured under light microscopy on undecalcified dry-mounted ground section of tibial compact bone from three adult males and three adult females not affected by metabolic bone disease. The measurement of the thickness of bony lamellae was carried out on the same samples under scanning electron microscopy. Statistical analyses of the results showed that the decrease in size of osteocytic lacunae from the outer to the inner osteonal wall is paralleled by a decrease in thickness of osteocytic loose lamellae. The fact that acellular dense lamellae do not follow such a decremental pattern, but remain of the same thickness throughout the osteonic wall, corroborates Marotti’s view that the formation of lamellar bone depends on the orderly distribution of the osteocytes in alternating planes. The topographical distribution of osteocyte lacunar size and lamellar thickness is briefly discussed in relation to secondary osteon mechanical function.