Constant mineralization density distribution in cancellous human bone.

The degree of mineralization of bone matrix is an important factor in determining the mechanical competence of bone. The remodeling and modeling activities of bone cells together with the time course of mineralization of newly formed bone matrix generate a characteristic bone mineralization density distribution (BMDD). In this study we investigated the biological variance of the BMDD at the micrometer level, applying a quantitative backscattered electron imaging (qBEI) method. We used the mean calcium concentration (Ca(Mean)), the most frequent calcium concentration (Ca(Peak)), and full width at half maximum (Ca(Width)) to characterize the BMDD. In none of the BMDD parameters were statistically significant differences found due to ethnicity (15 African-American vs. 27 Caucasian premenopausal women), skeletal site variance (20 ilium, 24 vertebral body, 13 patella, 13 femoral neck, and 13 femoral head), age (25 to 95 years), or gender. Additionally, the interindividual variance of Ca(Mean) and Ca(Peak), irrespective of biological factors, was found to be remarkably small (SD < 2.1% of means). However, there are significant changes in the BMDD in the case of bone diseases (e.g., osteomalacia) or following clinical treatment (e.g., alendronate). From the lack of intraindividual changes among different skeletal sites we conclude that diagnostic transiliac biopsies can be used to determine the BMDD variables of cancellous bone for the entire skeleton of the patient. In order to quantify deviations from normal mineralization, a reference BMDD for adult humans was calculated using bone samples from 52 individuals. Because we find the BMDD to be essentially constant in healthy adult humans, qBEI provides a sensitive means to detect even small changes in mineralization due to bone disease or therapeutic intervention.