Alendronate increases degree and uniformity of mineralization in cancellous bone and decreases the porosity in cortical bone of osteoporotic women

The strength of bone is correlated with bone mass but is also influenced si gnificantly by other factors such as structural properties of the matrix (e .g., collagen mutations) and the mineral. Changes at all levels of this org anization could contribute to fracture risk. We investigated the effects of alendronate (Ain) treatment on the density of mineralization and the ultra structure of the mineral/collagen composite, size and habitus of mineral pa rticles in iliac cancellous bone, as well as on the porosity of iliac corti cal bone from postmenopausal osteoporotic women. Twenty-four transiliac bon e biopsies from Phase III Ain (10 mg/day) trials (placebo and Ain after 2 a nd 3 years of treatment, n = 6 per group) were studied. The mineral structu re was investigated by quantitative backscattered electron imaging (qBEI) a nd by scanning small-angle X-ray scattering (scanning-SAXS). qBEI histogram s reflect the bone mineralization density distribution (BMDD), whereas SAXS patterns characterize the size and arrangement of the mineral particles in bone. We found that: (i) the relative calcium content of osteoporotic bone was significantly lower than that of data-base controls; (ii) mineralizati on was significantly higher and more uniform after Ain treatment; (iii) siz e and habitus of the mineral particles was not different between placebo an d Aln-treated groups; and (iv) the porosity of cortical bone was reduced si gnificantly by Ain treatment. We conclude that Ain treatment increases the degree and uniformity of bone matrix mineralization without affecting the s ize and habitus of the mineral crystals. It also decreases the porosity of the corticalis. Together these effects may contribute to the observed reduc tion in fractures. (C) 2001 by Elsevier Science Inc. All rights reserved.