title: Experimental and finite element analysis of strains induced by axial tibial compression in young-adult and old female C57Bl/6 mice.
abstract: Axial compression of the mouse tibia is used to study strain-adaptive bone (re)modeling. In some studies, comparisons between mice of different ages are of interest. We characterized the tibial deformation and force-strain relationships in female C57Bl/6 mice at 5-, 12- and 22-months age. A three-gauge experimental method was used to determine the strain distribution at the mid-diaphysis, while specimen-specific finite element analysis was used to examine strain distribution along the tibial length. The peak strains in the tibial mid-diaphyseal cross-section are compressive and occur at the postero-lateral apex. The magnitudes of these peak compressive strains are 1.5 to 2 times those on the opposite, antero-medial face (a site often used for strain gauge placement). For example, -10 N force applied to a 5-months old mouse engenders a peak compressive strain of -2800 µε and a tensile strain on the antero-medial face of +1450 µε. The orientation of the neutral axis at the mid-diaphysis did not differ with age (p=0.46), indicating a similar deformation mode in young and old tibiae. On the other hand, from 5- to 22-months there is a 25% reduction in cortical thickness and moment of inertia (p<0.05), resulting in significantly greater tibial strain magnitudes in older mice for equivalent applied force (p<0.05). We conclude that comparisons of tibial loading responses in young-adult and old C57Bl/6 tibiae are facilitated by similar deformation pattern across ages, but that modest adjustment of force levels is required to engender matching peak strains.
authors.affiliation: Musculoskeletal Research Center and Department of Orthopaedic Surgery, Washington University School of Medicine, 660 South Euclid Avenue, Campus Box 8233, St. Louis, MO 63110, USA.
authors.forename: Tarpit K
authors.initials: TK
authors.lastname: Patel
authors.affiliation: Musculoskeletal Research Center and Department of Orthopaedic Surgery, Washington University School of Medicine, 660 South Euclid Avenue, Campus Box 8233, St. Louis, MO 63110, USA.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Brodt
authors.affiliation: Musculoskeletal Research Center and Department of Orthopaedic Surgery, Washington University School of Medicine, 660 South Euclid Avenue, Campus Box 8233, St. Louis, MO 63110, USA. Electronic address: silvam@wustl.edu.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Silva
mesh_terms: D000375:Aging / Q000473:pathology / Q000502:physiology*; D000818:Animals; D016723:Bone Remodeling; D003430:Cross-Sectional Studies; D018483:Diaphyses / Q000502:physiology; D005260:Female; D020342:Finite Element Analysis; D051379:Mice; D008810:Mice, Inbred C57BL; D011897:Random Allocation; D013314:Stress, Mechanical; D013977:Tibia / Q000473:pathology / Q000502:physiology*; D016474:Weight-Bearing / Q000502:physiology
keywords: Aging; Bone adaptation; In vivo loading; Mouse tibia; Tibial compression