title: Remodeling of fracture callus in mice is consistent with mechanical loading and bone remodeling theory.
abstract: During the remodeling phase of fracture healing in mice, the callus gradually transforms into a double cortex, which thereafter merges into one cortex. In large animals, a double cortex normally does not form. We investigated whether these patterns of remodeling of the fracture callus in mice can be explained by mechanical loading. Morphologies of fractures after 21, 28, and 42 days of healing were determined from an in vivo mid-diaphyseal femoral osteotomy healing experiment in mice. Bone density distributions from microCT at 21 days were converted into adaptive finite element models. To assess the effect of loading mode on bone remodeling, a well-established remodeling algorithm was used to examine the effect of axial force or bending moment on bone structure. All simulations predicted that under axial loading, the callus remodeled to form a single cortex. When a bending moment was applied, dual concentric cortices developed in all simulations, corresponding well to the progression of remodeling observed experimentally and resulting in quantitatively comparable callus areas of woven and lamellar bone. Effects of biological differences between species or other reasons cannot be excluded, but this study demonstrates how a difference in loading mode could explain the differences between the remodeling phase in small rodents and larger mammals.
authors.affiliation: AO Research Institute, Davos, Switzerland.
authors.forename: Hanna
authors.initials: H
authors.lastname: Isaksson
authors.forename: Ina
authors.initials: I
authors.lastname: Gröngröft
authors.forename: Wouter
authors.initials: W
authors.lastname: Wilson
authors.forename: Corrinus C
authors.initials: CC
authors.lastname: van Donkelaar
authors.forename: Bert
authors.initials: B
authors.lastname: van Rietbergen
authors.forename: Andrea
authors.initials: A
authors.lastname: Tami
authors.forename: Rik
authors.initials: R
authors.lastname: Huiskes
authors.forename: Keita
authors.initials: K
authors.lastname: Ito
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D016723:Bone Remodeling / Q000502:physiology*; D002146:Bony Callus / Q000000981:diagnostic imaging*; D003198:Computer Simulation; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging / Q000293:injuries; D005594:Fracture Fixation, Intramedullary; D017102:Fracture Healing / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D055114:X-Ray Microtomography