Stereologic estimators of cortical bone remodeling including a kinetic model

The purpose of this study was to describe cortical bone remodeling by means of a new stereologic model, which is based on isotropic uniform (IUR) histological sections and two fluorochrome tissue time markers (tetracycline and calcein) given with a 15-day interval. From each of five pigs two samples of cortical bone were sawed out from the middle part of the diaphysis of the left femoral bone and fixed in absolute methanol. Specimens were embedded undecalcified in methylmethacrylate, and the plane of sectioning was sampled by a new procedure, which produce IUR-sections. The extent of remodeling was estimated by length densities, that is, length of Haversian system undergoing resorption or formation per unit volume of bone. These estimates made it possible to express the activation rate and the remodeling rate at tissue level in absolute three-dimensional terms. Such estimates have not previously been published. The shortest diameter of osteon cross-sections was used for obtaining three-dimensional measures of osteons dimensions. The estimated true variance between animals as percentage of the observed variance was above 68% for all morphometric parameters except the length density of resorptive osteons (35%). It was concluded that the proposed stereologic methods enable a detailed description in three-dimensional terms of the remodeling process in cortical bone, and further information may be obtained by combining measurements with observations of cell morphology.