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“Introduction Daily injections of parathyroid hormone (PTH) have anabolic effects on bone and are Food and Drug Administration approved for treatment of vertebral fractures associated with postmenopausal osteoporosis. The effects of PTH have been extensively studied in the ovariectomized rat. This is an animal model that has been shown to be a good first predictor of treatment potential of a EX 527 molecular weight drug for osteoporosis and as such is commonly used. PTH markedly increases trabecular bone mass in the proximal tibia, LCZ696 order femoral neck, and lumbar vertebra of ovariectomized, aged, and young rats [1–15]. Additionally, it increases cortical
width, MK5108 solubility dmso cortical bone area, and axial moments of inertia as a result of mostly endocortical bone formation, leading to reduced bone marrow cavities and, to a lesser extent, increased periosteal bone formation [7, 16–18]. Mechanical strength in anatomical sites like the vertebra, femoral neck, and femoral diaphysis increases accordingly in
rats after PTH treatment [2–4, 9]. Although the effects of PTH have been extensively studied, some aspects are still unclear and need further research. Although most increases in trabecular bone mass after Dynein PTH treatment have been reported to result from increased trabecular thickness, in a few studies in dogs, rodents, and monkeys, an increase in trabecular number was reported after PTH treatment [19–25], which is an uncommon feature in itself. The suggested mechanism for this was the observation of longitudinal tunneling of thickened trabeculae seen in histological sections as a remodeling mechanism to maintain trabecular thickness within limits. Tunneling of thickened individual trabeculae would convert them into multiple trabeculae, resulting in a normalization of trabecular thickness and an increase in trabecular number. It has been suggested that trabecular thickness will increase until it reaches a maximum, after which intratrabecular resorption will take place [23]. This suggests that changes in trabecular number and thickness may depend on the structure at the start of the treatment and may vary over time depending on dose and duration of treatment and anatomical site. It is known that the same increase in bone mass due to trabecular thickness or number has different mechanical implications, with the latter one having a higher increase in mechanical performance [26, 27].