Adaptation of Bone in Response to Osteoporosis

In an early FT-IR imaging study, compositional differences between iliac crest biopsies from untreated osteoporotic patients and normal controls were examined 

More detailed FT-IR imaging of specimens from human ibac crest biopsies showed that mineralization in untreated osteoporotic trabecular bone samples was decreased by 40% from the normal, and the mineral mateix ratio was lower in the center of trabeculae (more mature tissue) than for controls [63]. The crystallinity ratio was also increased in osteoporotic specimens. Differences between the trabecular bone matrix of osteoporotic and normal bone have also emerged [64]. 

The spatial variation of crosslinks at bone-forming trabecular surfaces (within 50 gm) in patients with osteoporotic or multiple spontaneous fractures was significantly different from that in normal bone, and the collagen crosslink ratio was higher. It has been hypothesized that the matrix produced in osteoporosis might mature more quickly or undergo post-translational modifications for a longer time than normal bone matrix. 

Ovariectomized (ovx) cynomolgus monkeys represent a common model for postmenopausal osteoporosis because they experience regular menstrual cycles, hormonal fluctuations and bone loss upon ovariectomy. Both, ovx monkeys and postmenopausal osteoporotic women showed similar modifications in trabecular mineral properties [65], specifically a decreased mineral matrix ratio, increased crystallinity and increased carbonate content relative to controls. In addition, the spatial variation in the mineral matrix ratio was the same in humans and monkeys. 

In contrast to trabecular bone, in the cortical bone of ovx monkeys the mineral content was significantly increased in endosteal regions, while the crystallinity and collagen crosslink ratio remained constant in both periosteal and endosteal tissue [66]. Because these parameters displayed different trends in cortical and trabecular bone, the compositional adaptations may be site-specific. 

---