Bending Properties, Porosity, and Ash Fraction of Cortical Bone from Black Bear (ursusamericanus) Tibias Are Not Compromised with Aging despite Annual Periods of Disuse

Introduction Osteoporosis is a disease characterized by low bone mass and structural deterioration of bone tissue, which leads to bone fragility and increased fracture risk. For prolonged bed rest, immobilization, and space flight, disuse atrophy of bone is prevalent in many animals including humans. However, black bears may not develop osteopenia during long periods of disuse (i.e., hibernation) to the extent that other animals do and they may have a mechanism for more rapid and complete bone recovery. The specific aims of this study were to evaluate the histological, compositional, and mechanical characteristics of tibias from annually hibernating black bears. Black bears are inactive during annual hibernation periods (approximately 6 months) and osteoclastic resorption increases during this time. However, because osteoblastic function does not decline during hibernation and is elevated during remobilization in the spring, we hypothesized that cortical bone porosity, mineral content, and mechanical properties are not compromised with aging despite annual 6 month periods of disuse.