Distribution of mineralization indices of modeling and remodeling over eight months in middiaphyseal cross sections of femurs from adult swine.

Abstract

This study assessed the distribution of active mineral formation sites within the middiaphyseal femoral cross section of swine and determined the extent to which various subsections represented bone formation activity in the entire cross section. Twenty adult female swine (sows) were injected with two double (10-day intervals) labels 8 months apart. Labels involved fluorochrome markers of active mineral formation sites. Intact femoral middiaphyseal cross sections were embedded in polymethylmethacrylate, cut, and ground to 80 microm for analysis. Each specimen was subdivided into 16 anatomical and eight geometric subsections. Labeled mineralizing surface and mineral apposition rate were determined in the periosteal and endocortical envelopes. The number of labeled osteons per unit area of bone and osteonal mineral apposition rate were determined in the intracortical envelope. Periosteal mineralizing surface followed a bimodal distribution with highest surface activation on the anterior and posterior segments. Periosteal mineral apposition rate followed a modal distribution with highest apposition rates in the posterior portion of the cross section. The distribution of forming osteons was modal with highest frequencies of labeled osteons in the posterior segment. No significant regional differences were detected for osteonal mineral apposition rate, endocortical mineralizing surface, or endocortical mineral apposition rate. The location of either a single or a combination of two to four subsections that best predicted mineralizing surface and mineral apposition rate in the entire cross section differed with each trait and envelope. Fifty percent of the entire area as alternate anatomical subsections was required to predict > 90% of variation in all traits evaluated. Overall, the predictability of mineralizing surface and mineral apposition rate was similar for geometrically defined subsections. At least 50% of the cross-sectional area from alternate anatomical subsections must be measured to predict > 90% of variation in periosteal, intracortical, and endocortical mineralizing surface and mineral apposition rate in the sow middiaphyseal femur.