Age variations in the specific surface of howship's lacunae as an index of human bone resorption

Internal remodelling of bone occurs continually during life in discrete foci throughout cortex and large trabeculae. It is defined as the process of replacement of primaryappositional bone with Haversian bone occurring within the periosteal‐endosteal envelope. The foci are produced by osteoclastic resorption of preexisting bone and are subsequently filled in by successive waves of osteoblasts that deposit new matrix. In this study, measurements of the surface area of Howship's lacunae in rib diaphysealcortex are presented for 137 relatively normal individuals of both sexes and ranging from one month to 84 years of age. Undecalcified cross‐sections were prepared fresh from rib obtained at thoracotomy or post‐mortem. Measurements were performed with a calibrated Zeiss Integrating Eyepiece II. It was found that the values for this resorption index were highest in infancy and lowest in middle and early adult life. The maximum adult values were attained in the seventh decade. No differences were noted that could be accounted for by sex. Correlation of these data with an index of secondary bone formation in this same group of bones enabled the authors to conclude that the internal remodelling rate of rib cortex is highest in infancy, lowest in the fourth decade and attains a secondary peak in the seventh decade. The authors suggest that the phasing of the changes noted are due to some as yet unknown programming of the mesenchymal cell. Since no increases coincided with growth spurts during childhood and adolescence, they conclude that the process of internal remodelling may be under a completely different mechanism of control from that governing skeletal growth and maturation.