Cellular activity on the seven surfaces of iliac bone: A histomorphometric study in children and adolescents

Transiliac cortical bone histomorphometry was performed in 56 metabolic bone disease-free individuals 1.5-22.9 years of age. During the growing years, the two cortices of an iliac bone specimen differ with regard to bone cell activity on their surfaces, probably reflecting a modeling drift. Introduction: Standard bone histomorphometry in the clinical setting is typically limited to the analysis of cancellous bone. However, during the growth period, important changes occur also in the cortical compartment. Materials and Methods: Transiliac bone samples from 56 individuals between 1.5 and 22.9 years of age (25 male; tetracycline labeling present in 42 subjects) and without evidence of metabolic bone disease were analyzed. Each of the three bone surface types (periosteal, intracortical, endocortical) of each cortex was evaluated separately. Results were expressed relative to those obtained in trabecular bone. Results: A significant increase in cortical width with age was detected only for the internal cortex. Porosity of the external cortex was highest in the 7- to 10.9-year age group and decreased thereafter, whereas there was no clear trend with age for the porosity of the internal cortex. Intracortical remodeling activity decreased after 1.4 years of age. Periosteal bone formation was very active until 13 years of age, but was close to zero in subjects above that age. As to endocortical surfaces, all bone surface-based parameters of bone formation were higher on the internal cortex than on the external cortex, whereas bone resorption parameters were higher on the external cortex. Conclusions: In growing subjects, the two cortices of an iliac bone specimen differ with regard to bone cell activity on their surfaces. These data raise fundamental questions about the regulation of bone cell activity in children and adolescents.