title: Fracture healing in mice under controlled rigid and flexible conditions using an adjustable external fixator.
abstract: Mice are increasingly used to investigate mechanobiology in fracture healing. The need exists for standardized models allowing for adjustment of the mechanical conditions in the fracture gap. We introduced such a model using rigid and flexible external fixators with considerably different stiffness (axial stiffnesses of 18.1 and 0.82 N/mm, respectively). Both fixators were used to stabilize a 0.5 mm osteotomy gap in the femur of C57BL/6 mice (each n = 8). Three-point bending tests, µCT, and histomorphometry demonstrated a different healing pattern after 21 days. Both fixations induced callus formation with a mixture of intramembranous and enchondral ossification. Under flexible conditions, the bending stiffness of the callus was significantly reduced, and a larger but qualitatively inferior callus with a significantly lower fraction of bone but a higher fraction of cartilage and soft tissue was formed. Monitoring of the animal movement and the ground reaction forces demonstrated physiological loading with no significant differences between the groups, suggesting that the differences in healing were not based on a different loading behavior. In summary, flexible external fracture fixation of the mouse femur led to delayed fracture healing in comparison to a more rigid situation.
authors.affiliation: Institute of Orthopaedic Research and Biomechanics, Center of Musculoskeletal Research, University of Ulm, Ulm, Germany.
authors.forename: Viktoria
authors.initials: V
authors.lastname: Röntgen
authors.forename: Robert
authors.initials: R
authors.lastname: Blakytny
authors.forename: Romano
authors.initials: R
authors.lastname: Matthys
authors.forename: Mario
authors.initials: M
authors.lastname: Landauer
authors.forename: Tim
authors.initials: T
authors.lastname: Wehner
authors.forename: Melanie
authors.initials: M
authors.lastname: Göckelmann
authors.forename: Philipp
authors.initials: P
authors.lastname: Jermendy
authors.forename: Michael
authors.initials: M
authors.lastname: Amling
authors.forename: Thorsten
authors.initials: T
authors.lastname: Schinke
authors.forename: Lutz
authors.initials: L
authors.lastname: Claes
authors.forename: Anita
authors.initials: A
authors.lastname: Ignatius
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001835:Body Weight; D016267:External Fixators; D005260:Female; D005264:Femoral Fractures / Q000503:physiopathology / Q000601:surgery; D017102:Fracture Healing; D051379:Mice; D008810:Mice, Inbred C57BL