title: Six months of disuse during hibernation does not increase intracortical porosity or decrease cortical bone geometry, strength, or mineralization in black bear (Ursus americanus) femurs.
abstract: Disuse typically uncouples bone formation from resorption, leading to bone loss which compromises bone mechanical properties and increases the risk of bone fracture. Previous studies suggest that bears can prevent bone loss during long periods of disuse (hibernation), but small sample sizes have limited the conclusions that can be drawn regarding the effects of hibernation on bone structure and strength in bears. Here we quantified the effects of hibernation on structural, mineral, and mechanical properties of black bear (Ursus americanus) cortical bone by studying femurs from large groups of male and female bears (with wide age ranges) killed during pre-hibernation (fall) and post-hibernation (spring) periods. Bone properties that are affected by body mass (e.g. bone geometrical properties) tended to be larger in male compared to female bears. There were no differences (p>0.226) in bone structure, mineral content, or mechanical properties between fall and spring bears. Bone geometrical properties differed by less than 5% and bone mechanical properties differed by less than 10% between fall and spring bears. Porosity (fall: 5.5+/-2.2%; spring: 4.8+/-1.6%) and ash fraction (fall: 0.694+/-0.011; spring: 0.696+/-0.010) also showed no change (p>0.304) between seasons. Statistical power was high (>72%) for these analyses. Furthermore, bone geometrical properties and ash fraction (a measure of mineral content) increased with age and porosity decreased with age. These results support the idea that bears possess a biological mechanism to prevent disuse and age-related osteoporoses.
authors.affiliation: Department of Biomedical Engineering, Michigan Technological University, 309 Minerals and Materials Engineering Building, 1400 Townsend Drive, Houghton, MI 49931, USA.
authors.forename: Meghan E
authors.initials: ME
authors.lastname: McGee-Lawrence
authors.affiliation: Department of Biomedical Engineering, Michigan Technological University, 309 Minerals and Materials Engineering Building, 1400 Townsend Drive, Houghton, MI 49931, USA.
authors.forename: Samantha J
authors.initials: SJ
authors.lastname: Wojda
authors.affiliation: Department of Biomedical Engineering, Michigan Technological University, 309 Minerals and Materials Engineering Building, 1400 Townsend Drive, Houghton, MI 49931, USA.
authors.forename: Lindsay N
authors.initials: LN
authors.lastname: Barlow
authors.affiliation: Department of Mathematical Sciences, Michigan Technological University, Houghton, MI 49931, USA.
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Drummer
authors.affiliation: Utah Division of Wildlife Resources, 1594 W. North Temple, Salt Lake City, UT 84116, USA.
authors.forename: Kevin
authors.initials: K
authors.lastname: Bunnell
authors.affiliation: Department of Integrative Biology, 401 WIDB, Brigham Young University, Provo, UT 84602, USA.
authors.forename: Janene
authors.initials: J
authors.lastname: Auger
authors.affiliation: Department of Integrative Biology, 401 WIDB, Brigham Young University, Provo, UT 84602, USA.
authors.forename: Hal L
authors.initials: HL
authors.lastname: Black
authors.affiliation: Department of Biomedical Engineering, Michigan Technological University, 309 Minerals and Materials Engineering Building, 1400 Townsend Drive, Houghton, MI 49931, USA. Electronic address: swdonahu@mtu.edu.
authors.forename: Seth W
authors.initials: SW
authors.lastname: Donahue
mesh_terms: D000375:Aging / Q000473:pathology / Q000502:physiology; D000818:Animals; D001363:Awards and Prizes; D001696:Biomechanical Phenomena; D015519:Bone Density; D016723:Bone Remodeling / Q000502:physiology; D005260:Female; D005269:Femur / Q000033:anatomy & histology / Q000502:physiology; D006605:Hibernation / Q000502:physiology*; D008297:Male; D012958:Societies, Scientific; D013314:Stress, Mechanical; D013997:Time Factors; D001503:Ursidae / Q000033:anatomy & histology* / Q000502:physiology*