PMC

Bone resorption, measured by eroded surface (ES/BS), typically increases in models of disuse including immobilization (IM), bedrest (BR) and spaceflight (SF). Increases in eroded surface were statistically significant in subjects under disuse compared to active conditions in the studies represented below (*: p < 0.05 vs. active group in each study). In contrast, hibernating grizzly bears in the current study did not demonstrate increased indices of bone resorption compared to active bears (p > 0.648). MC2 = 2^nd metacarpal, DF = distal femur. Means + SE bars are presented.

Trabecular bone does not respond similarly to disuse in bears and sheep. Trabecular bone volume fraction was decreased by 31% in sheep calcanei following 12 weeks of immobilization (A). Representative micro-computed tomography (μCT) scans from the distal femoral epiphysis of 1-year old (B) and 18-year old (C) grizzly bears demonstrate no bone loss after 17 weeks of disuse (hibernation). Sheep calcaneus images are reproduced with permission from: Calcif Tissue Int 42, Rubin, C. T. et al., “Ultrasonic measurement of immobilization-induced osteopenia: an experimental study in sheep,” pp. 309-312, copyright Springer-Verlag, New York Inc. (1988).