title: A new model to analyze metaphyseal bone healing in mice.
abstract: BACKGROUND
  Despite the increasing clinical problems with metaphyseal fractures, most experimental studies investigate the healing of diaphyseal fractures. Although the mouse would be the preferable species to study the molecular and genetic aspects of metaphyseal fracture healing, a murine model does not exist yet. Using a special locking plate system, we herein introduce a new model, which allows the analysis of metaphyseal bone healing in mice.
  
  
  METHODS
  In 24 CD-1 mice the distal metaphysis of the femur was osteotomized. After stabilization with the locking plate, bone repair was analyzed radiologically, biomechanically, and histologically after 2 (n=12) and 5 wk (n=12). Additionally, the stiffness of the bone-implant construct was tested biomechanically ex vivo.
  
  
  RESULTS
  The torsional stiffness of the bone-implant construct was low compared with nonfractured control femora (0.23 ± 0.1 Nmm/°versus 1.78 ± 0.15 Nmm/°, P<0.05). The cause of failure was a pullout of the distal screw. At 2 wk after stabilization, radiological analysis showed that most bones were partly bridged. At 5 wk, all bones showed radiological union. Accordingly, biomechanical analyses revealed a significantly higher torsional stiffness after 5 wk compared with that after 2 wk. Successful healing was indicated by a torsional stiffness of 90% of the contralateral control femora. Histological analyses showed new woven bone bridging the osteotomy without external callus formation and in absence of any cartilaginous tissue, indicating intramembranous healing.
  
  
  CONCLUSIONS
  With the model introduced herein we report, for the first time, successful metaphyseal bone repair in mice. The model may be used to obtain deeper insights into the molecular mechanisms of metaphyseal fracture healing.
authors.affiliation: Department of Trauma, Hand and Reconstructive Surgery, University of Saarland, Homburg/Saar, Germany. tina.histing@uks.eu
authors.forename: Tina
authors.initials: T
authors.lastname: Histing
authors.forename: Moritz
authors.initials: M
authors.lastname: Klein
authors.forename: Andrea
authors.initials: A
authors.lastname: Stieger
authors.forename: David
authors.initials: D
authors.lastname: Stenger
authors.forename: Roland
authors.initials: R
authors.lastname: Steck
authors.forename: Romano
authors.initials: R
authors.lastname: Matthys
authors.forename: Joerg H
authors.initials: JH
authors.lastname: Holstein
authors.forename: Patric
authors.initials: P
authors.lastname: Garcia
authors.forename: Tim
authors.initials: T
authors.lastname: Pohlemann
authors.forename: Michael D
authors.initials: MD
authors.lastname: Menger
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D005260:Female; D017102:Fracture Healing / Q000502:physiology*; D051379:Mice; D008813:Mice, Inbred ICR; D023421:Models, Animal; D010027:Osteotomy